# Twist Drill Angle with Center Drills vs Spotting Drills



## wildo

I read this message from Bob and it got me thinking. I didn't even recognize the difference in twist drill split point angle (note the beginner's forum!) but when checking my drill bits, I find them to be 135 degree tips. Sigh, and I just ordered a set of 60 degree center drills. Looking at 140 degree spot drills- they seem to be quite a bit more expensive.


Can I use these 60 degree center drills with my 135 degree drill bits? I mean- better than nothing, right?
Why does it seem that 135 degree twist drills are far more common than 118 degree?
Besides accounting for the drill bit tip angle, when does one use a spotting drill vs a center drill? What is the intended purpose of those two things? I had never heard of a spotting drill before.
Does there exist a 140 degree (or maybe it's 70 degree?) center drill?
Is it worth investing in a couple $30 spotting drills, or buying a whole new set of 118 degree twist bits?

Seems like some good advice below, Bob. Just looking to fill in some holes in my understanding.


Bob Korves said:


> I am assuming the main drill has a 118 degree point angle here.  The starting tip of the center drill is ground at 120 degrees.  The spotting/center drill should have a LARGER angle than the drill that follows for it to follow with proper guidance, not walking around as the cutting lips make contact with a 90 degree hole part way out on the cutting lips, which leads to chatter and poor following.  The chisel point of the larger drill should be first to contact the work in the starter hole and start cutting, with the cutting lips taking over the job from the center outward, not starting by taking notches from some random points on the cutting lips.  In this way the starter hole is truly guiding the drill.
> 
> Using the 60 degree main cutting portion of a center drill to make a starting hole for a drill is a really poor idea, even worse than the 90 degree spotting drill, but it is very commonly done.  Using the parallel bore caused by the entire tip of the center drill penetrating the work is not quite as bad, but still wrong, and is also sometimes done in error.
> 
> Again, the only way a starting drill can facilitate centering of the drill and locating where the drill should follow is for the included angle of the starting/spotting drill to be slightly larger than the drill which will follow.  That would mean a 120 degree spotting drill for a 118 degree drill to follow, and a 140 degree spotting drill for a 135 degree drill to follow.
> 
> I understand quite well that what I am posting here is not common practice.  If you disagree with it, please explain to me why it is wrong.
> 
> Specifically, in the case of starting a hole in a curved surface, which is what the OP was trying to do, the center drill is a pretty good choice because it is extremely rigid, has a 120 degree starting angle, and can leave a small, well centered starting hole if pecked lightly and carefully, avoiding the need for milling the curved surface flat first, which would be probably be best for higher precision work.  A spotting drill has a larger chisel point and is also less rigid than the center drill is, and is therefore more likely to walk off the curved surface.
> 
> Does that make sense?  It has worked well for me...


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## Bob Korves

60 degree center drills are designed for drilling centers on a lathe for use with 60 degree center in the tailstock.  They also are used for other things, including spotting holes for drilling.  Millions, no, billions of holes have been started with 60 degree center drills, and they do work for that job.  The most common point angle for drills is 118 degrees, a general purpose grind.  Flatter point angles are for harder materials, though I include all steels in that group.  Softer materials can be cut with 135 degree drills, though somewhat slower.  Split points are better at drilling holes in flat and perpendicular surfaces without any spotting, and they also require less pressure to feed them into the work.  To me it makes much more sense to use a larger angle spotting drill than the main drill, but I am quite sure that many others disagree, if only because they have been doing so as long as they have been drilling holes.  Try drilling a bunch of holes both ways and see what you prefer...


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## wildo

Oh good! I'm glad to know that I didn't get the "wrong" center drills since my primary application is indeed starting holes on the lathe (or maybe in the mill). I guess I'm still a little confused about the purpose or point of the spotting drill, but I think this might be in definition alone. If I had to take a guess at what "spotting" a hole means, I'd imagine it meant to start the hole in the correct location. IF that's true, one could claim (maybe?) that a center drill is a specialized type of spotting drill since it is also used for starting the hole in the correct location, namely- the center of spinning stock. Am I on track here?

If all that's true, then I'd infer that a center drill is for starting a hole specifically on a lathe, and a spotting drill is for starting a hole everywhere else. Yes?


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## Bob Korves

I really prefer to use no starter drill, just a 135 degree split point screw machine (stub) length drill which is stiffer, will not walk on the work, and will center itself.  Starter drills are a major waste of time.


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## Bob Korves

Here is a link on the subject.  Do note it is on a CNC site, but that doesn't change much:
http://blog.cnccookbook.com/2017/02/27/when-to-use-a-spot-drill/


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## mikey

wildo said:


> Oh good! I'm glad to know that I didn't get the "wrong" center drills since my primary application is indeed starting holes on the lathe (or maybe in the mill). I guess I'm still a little confused about the purpose or point of the spotting drill, but I think this might be in definition alone. If I had to take a guess at what "spotting" a hole means, I'd imagine it meant to start the hole in the correct location. IF that's true, one could claim (maybe?) that a center drill is a specialized type of spotting drill since it is also used for starting the hole in the correct location, namely- the center of spinning stock. Am I on track here?
> 
> If all that's true, then I'd infer that a center drill is for starting a hole specifically on a lathe, and a spotting drill is for starting a hole everywhere else. Yes?



Wildo, Bob has given you accurate and very good advice. I just wanted to try to clarify some points of confusion. A center drill is intended to do what the name says - drill an accurate hole with the proper taper to fully seat a center, a dead or live center. Back in the day, dead centers were common and the tip of the center drill created a reservoir to hold lubricant; as the work piece heated up, the oil moved from this reservoir towards the taper to provide lubrication. In the USA, tailstock centers typically have a 60 degree taper and our center drills have a matching taper so they are actually the appropriate tool for only this purpose.

However, in addition to drilling holes for centers on a lathe, many guys use center drills as a general purpose hole locator. The tiny tip of the drill fits nicely into a center-punched hole and it begins to cut immediately; the taper it cuts tends to center the main drill that follows ... logical, right? The problem with this is what Bob pointed out. The taper created by a center drill allows the cutting edges of the flutes to contact first, not the tip of the drill, and this can damage the cutting edges of the drill. In soft materials this is not a major deal but it can be in hard materials or if you're using a carbide drill. You will definitely see this effect when using tiny carbide drills; they can snap when a cutting edge catches.

The ideal situation when drilling a hole is for the center of the drill to contact first and then gradually and continually engage the adjacent cutting edges as you apply downward force to begin the actual drilling operation. This locates the drill accurately and avoids impact damage to the cutting edges. This what a spotting drill does. The angle of the spotting drill is ideally wider than the angle of the tip of the drill and the center of the divot it creates allows the tip of the main drill to engage first, just at the center to eliminate walking of the drill. As you push the drill into the cut the cutting edges gradually engage, maintaining accuracy and avoiding damage to those edges. If the angle of the spotting drill is narrower than the main drill's tip, the cutting edges hit first and this can lead to damage to those edges, chatter and an inaccurate hole. This is what Bob alluded to and why he recommended that the angle of the spotting drill be wider than the main drill - to ensure the center of your main drill contacts before the edges.

We have all step-drilled larger holes. We drill a pilot hole first and follow with larger and larger drills until we get the hole size we want. The problem with this is that in every case, the cutting edges are hitting first. This is why we often have a chewed up, inaccurate hole as the drill bounces around on those flutes.

The most accurate way to drill a hole is to spot it first, then use an on-size drill without using pilot drills or stepping up in size. As long as the angle of your spotting drill is larger than the tip of your main drill, the center will hit first and the drill will smoothly engage the hole and cut cleanly. You will find that your drills will cut rounder, more accurate holes. The drill will also not tend to grab and this is worth remembering; when drilling brass, go directly to an on-size drill and it won't grab on you. If you drill a pilot hole in brass first, I guarantee the drill will grab on you. Avoid the pilot drill and save yourself a lot of peck-drilling. It is also good to know that you do not need to drill deep with a spotting drill; just go deep enough to locate the main drill and it will work fine.

As Bob indicates, you can drill without a spotting drill provided the drill is sharp and properly ground and the surface has no irregularities. If these conditions are not present then a spotting drill is appropriate. For me, I try to always use a spotting drill but if I don't then I try to use my screw machine drills.

So, use center drills for drilling holes for your live or dead center on the lathe. Use spotting drills with a cutting angle wider than your drills for all other jobs. Hope this makes sense.


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## wildo

The amount of knowledge here is just crazy. Extremely good stuff... Thanks guys!


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## mikey

I totally forgot to add that when choosing a spotting drill, it only has to be big enough to span the web of the main drill. A 1/4" spotting drill will work for most drills in your drawer up to and including 1/2". If your drills are 118 degree points, use a 120 degree spotting drill. If using 135 degree split points, a 140 degree spotting drill works.


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## Bob Korves

mikey said:


> I totally forgot to add that when choosing a spotting drill, it only has to be big enough to span the web of the main drill. A 1/4" spotting drill will work for most drills in your drawer up to and including 1/2". If your drills are 118 degree points, use a 120 degree spotting drill. If using 135 degree split points, a 140 degree spotting drill works.


Exactly how I see things, too, Mike.  As long as the chisel point gets into the spotting cone, it is big enough.  Some drills have thinned flutes, so it is the chisel point size that needs to fit in the spotting hole, though a little oversize spotting hole does not hurt anything.  The main drill cutting edges should not contact anything until the chisel point has established the hole location.  The sides of the spotting drill should never enter the hole, it should be a pure cone, no cylinder portion at all.


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## David S

Lots of good information here, thank you.
Now I am looking for affordable spotting drills and find that 90 degrees seems to be very popular.

When would one use a 90 degree spotting drill?

David


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## Bob Korves

David S said:


> When would one use a 90 degree spotting drill?


I have no idea, but you are correct that it is popular.  120 degree spotters are less common, but out there, and 140 degree spotters are like hen's teeth.  I think a lot of this is due to sources of information, some of them mainstream and from well respected sources, that say the spotting drill should have a smaller angle than the following drill.  I have never been able to get my head around their reasoning...

A spotting drill can be carefully ground to whatever point angle is desired with the right fixture and skills.


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## mikey

David S said:


> When would one use a 90 degree spotting drill?



David, supposedly, 90 degree spotting drills are for use with HSS or cobalt drills, while the 120-140 degree spotting drills are for carbide drills with more brittle flutes. Carbide drills do not tolerate impact at the corners of the flutes and can chip; supposedly, HSS can tolerate impact.

The problem I have with this concept is that impact is impact. Spotting with a 90 degree drill is okay for softer stuff but try it in harder stuff like 4140 or even 1144 and the drill can jump on contact; this is most noticeable with smaller drills. I've had this happen enough to just prefer a wider angle on my spotting drills. Besides, I'd rather just stock 120's and not have to wonder which drill I'm grabbing. I normally use cobalt drills in harder stuff and my drills stay sharper longer with a 120 - just my personal observation.


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## David S

Mike thank you very much.

Against all my better (read cheap) judgement I went to my local industrial supply guy today and ordered a 1/4" hss, 120° spotting drill.  Bugs me that they are more expensive than I think they should be.

However that aside.  I am glad the OP brought this thread up, and everything makes sense to me.

David


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## Bob Korves

David S said:


> Mike thank you very much.
> 
> Against all my better (read cheap) judgement I went to my local industrial supply guy today and ordered a 1/4" hss, 120° spotting drill.  Bugs me that they are more expensive than I think they should be.
> 
> However that aside.  I am glad the OP brought this thread up, and everything makes sense to me.
> 
> David


They last just about forever...  Get a 140 degree as well...


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## EmilioG

I've been testing both spot and center drills for starting holes and finding punch marks, but now
stick with one drill, spot and drill and/or use a 142° Guhring spot drill.  I've made that mistake of using
a narrow spot with a wider drill point and got horrible chatter when the drills lips hit the side of an improper spot.  
I found out the hard way. So I now I choose my drills and spot drills carefully.  Great information here.
I also found that running carbide spot drills faster preserves the tool.


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## darkzero

When I was researching on which spotting drills to buy, I found conflicting answers. Some guys say to use a spotting drill with a lower angle than the drill so the flutes contact first & create a sort or counterbore for the drill to follow, then some say to use a spotting drill that has a wider angle than the drill so the tip of the drill contacts the workpiece first.

The guys stating you should use a smaller angle spotting drill say you don't want the tip of the drill bit to contact first as the chisel point will tend to wander. Then the guys who say to use a wider angle spotting drill say you don't want the flutes to contact first cause if they were ground uneven you will get wander as well as for carbide drills cause the flutes could chip.

There's also info saying you should not have to use a spotting drill with carbide drills cause they are stout, are designed to be used without a starter, and the flutes will chip in harder materials which they are generally used for. So as mentioned, the spotting drill angle also is dependent on the type & material of the drill bit as well as the hardness of the material being drilled.

Then there are guys saying you should use a spotting drill that in between, so neither the outter most edge of the flutes or the tip of the drill should contact first but rather in the middle of the flute.

I forget who but I only found recommendations by manufacturers & in documents saying you should use wider than the drill angle like most are saying here, never the opposite. They guys saying the opposite are machinists by trade, saying "I've never had a problem, or I've been doing it this way for x amount of years, yadda yadda".

Well I went with spotting drills wider than the following drill bit. I mostly use 135° split points so I got a 140° spotter but I also picked up some 120° just to have for my 118s. But makes you wonder cause those 140 & 120 spotting drills are less common. 90° seemed to be the most common (at the time). I don't own a full set of screw/stub length drills yet but one day I will. I think I only own a few in one size only that I bought for 6/32 tap hole size.

One thing I found was 90° seemed to be popular with CNC guys cause it saves a countersinking operation. They would spott drill a bit deeper for a larger dia then the following drill hole size to provide a chamfer so no need to chamfer or deburr the hole after it is drilled.


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## Bob Korves

I have a hard time understanding how a small chisel point of slightly smaller angle than the spotting drill cone can wander compared to the cutting edges making first contact a large percentage of the radius out from the center, which I consider a recipe for grabbing, chattering, walking, and making lobed holes -- and I have seen and experienced those issues, and it is why I changed to a wider spotting drill angle, and those problems have gone away.


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## darkzero

Exactly why I chose to go with the wider angle spotter. I used to use center drills for spotting too, we all have, and I admit, I still tend to it do it ever so often with soft materials where it doesn't matter to me. But the chatter & sound it makes (in harder materials ) alone tells me it can't be  right. Don't get that with the wider angle spotter drills. And my holes don't tend to wander as it did sometimes using center drills.


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## mikey

darkzero said:


> I used to use center drills for spotting too, we all have, and I admit, I still tend to it do it ever so often with soft materials where it doesn't matter to me.



*I* never used a center drill to spot a hole, oh no, not me ... you see, like Tom (@higgite ), I'm a genius!


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## higgite

I just call my center drills spotting drills. It’s cheaper, makes me sound smarter and I get fewer disparaging remarks that way. Us frugal geniuses don’t cotton too well to disparaging remarks.

But, after digesting this thread, I can see an authentic spotting drill or two in my future. New goodies! Yes!

Tom


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## Bob Korves

Actually, using just the small tip of a center drill as a spotting drill is a fairly good idea.  Those center drills are massively rigid, and the 118 degree point will spot a hole for a 118 or less angle drill.  You just need to make sure not to let the center drill penetrate the work beyond the angled point.  It usually takes a larger center drill to be useful for this strategy.


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## ericc

Bob, that is a good strategy.  I think I saw someone do it on Youtube.  Big center drills can often be found used for very low prices.


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## David S

Ya Bob why didn't you suggest that BEFORE I just ordered one for $22.  

David


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## mikey

higgite said:


> I just call my center drills spotting drills.



Tom, you always make me smile!


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## Jimsehr

I grind all my drills by hand and split the point on allmost all of them and if I need a spotting drill to match the drill I 'm using I grind it out of an old broken center or any old stub drill I have laying around. I bought two drill grinding machines but I am to lazy to learn how to use them. I started to grind drills in 1954 so it is hard to break the habit.
Jimsehr
I  even split the points on center drills.


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## mikey

Jim, you da' Man! I can barely see the tip of a center drill anymore, much less attempt to split the point. I used to hand grind all my drills too but as I got older I also got lazier and my eyes got blurrier so I went to a Drill Doctor. Now I can grind drills and split points but I'm still working on the lazy part.


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## Mutt

Bob Korves said:


> Here is a link on the subject.  Do note it is on a CNC site, but that doesn't change much:
> http://blog.cnccookbook.com/2017/02/27/when-to-use-a-spot-drill/




Ok, so say all my drills are 118º .  If I use a 60º center drill to spot drill  a piece in the lathe chuck, the drill would start cutting some where else on the drills face, rather than the drill's point? So if I used a spot drill, it would need to be 120º, to make the  drill bit actually start drilling at the drill bit's tip?


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## Bob Korves

Mutt said:


> Ok, so say all my drills are 118º .  If I use a 60º center drill to spot drill  a piece in the lathe chuck, the drill would start cutting some where else on the drills face, rather than the drill's point? So if I used a spot drill, it would need to be 120º, to make the  drill bit actually start drilling at the drill bit's tip?


Correct.


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## David S

This is really embarrassing having been doing this wrong all these years.  Even the "pros" use regular centre drills.

David


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## Bob Korves

David S said:


> This is really embarrassing having been doing this wrong all these years.  Even the "pros" use regular centre drills.
> 
> David


If you ask 10 machinists at random, most will say that the advice in this thread is all wrong.  Try what we are saying here, and see how it works for you in your shop.


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## markso125

As for both as someone who has machined in shops for years, and also taught for years i can say from my experience centerdrills are used almost exclusively.
The reasons for this is accuracy and cost. The design of the tool keeps it very rigid thus making it very accurate, usually we find play in the machine causing holes to be off before we find the center drill walking.
The next is cost, a center drill is used for all materials, for all different machines. They are cheap, they all act the same and you don't have to waste time deciding which angle you need to use. We run them in everything from 15-5PH to 6061t6 and always have predictable results.
As for common drill angle, the vast majority of  jobber drills are sold are at 118 degrees again this is the same as the center drills it is cost and predictability. Time spent checking angles for proper material in accordance with the cost of having a whole bunch of extra drills sounds counterproductive and more expensive to me.


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## JR49

markso125 said:


> the vast majority of jobber drills are sold are at 118 degrees again this is the same as the center drills



Could someone please explain this quote ?  I'm pretty sure all center drills are 60 deg. combined angle, while the drills markso125 mentioned is 118 deg. combined.  Unless he is referring to the tiny tip of the center drill, which (don't know for sure) might be 118 deg. or more but, if that is the case, wouldn't you need a HUGE center drill for the tip to be big enough to spot for even a fairly small dia. (say 3/8") final size drill.  Thanks,  JR49

EDIT: OK, I don't usually post things unless I'm 100% sure that what I'm saying is correct (which is why I don't post a lot, still a beginner).  So, after submitting this reply, I went out and checked my center drills with some 118 deg. drills.  It turns out that the tip of a #6 center drill will spot a hole big enough for a 3/4" main drill, and , as close as I could check, the tip is ground to 120 deg.  I don't know how big center drills get, but the #6 was the biggest I had.  So, like someone said up above, I guess yesterday I spent approx. 40 bucks on 2 spotting drills for nothing, except that::   "He who dies with the most tools WINS !!   JR49


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## David S

I am in the process of modifying a jig that I made and have to relocate some holes accurately.  So decided to try Bob's suggestion.  I have a #5 centre drill.  The main body is 7/16" Ø, and the "small" tip is 0.187Ø.  I am spotting for a # 27 drill.  And of course it works great.  

And yes you only use the tip.  The #5 is very stiff.

It is a slow week if I can't learn something.

David


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## JR49

David S said:


> I am in the process of modifying a jig that I made and have to relocate some holes accurately.  So decided to try Bob's suggestion.  I have a #5 centre drill.  The main body is 7/16" Ø, and the "small" tip is 0.187Ø.  I am spotting for a # 27 drill.  And of course it works great.
> 
> And yes you only use the tip.  The #5 is very stiff.
> 
> It is a slow week if I can't learn something.
> 
> David


I was typing when you posted this, thanks, and please see the edit to my post.   JR49


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## David S

Ah JR we both got sucked into buying expensive spotting drills I see.  And of course Bob waited 'till we had parted with our money to suggest a low cost....already have...alternative.

All in good fun my friends... and again really glad that the OP started this thread...who would have thunk?

David


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## JR49

David S said:


> And of course Bob waited 'till we had parted with our money to suggest a low cost....already have...alternative.



I know, how could Bob do that to us!!  But actually, the link that Bob provided in post #5, sites about 4 other good uses for spotting drills, so all is good.  Thanks Bob.  Oh, and I forgot to say before that this has been an extremely informative thread, so thanks to the OP, for asking the question.  These are the BEST threads, in my opinion.   Happy Machining,  JR49


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## JPMacG

Thank you everyone!   This thread has been very helpful and very timely for me.


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## mikey

The best fun we have on HM is to get someone else to spend money on a tool. I tried it with @higgite but he wouldn't bite until I bought the tool myself and showed him the results. Sometimes we go to extreme measures to get the job done but we do get it done!


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## LazyboyNZ

Really good thread, I have learnt a lot.
Thanks


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## Grandpop

I was a tool and die maker for 25 years before I left the field for a desk job. In that time I must have drilled about a million holes, and always in harder tool steels. We made high production dies that could have the inserts replaced when trey were dull, so the hole locations had to match the drawing. 

Most were located with a center drill, some were center punched from the described line intersections. Rarely did anything not line up, and typically could expect the final hole after center drill start to be in location within .005 . Not saying the spotting drills would not have been better, just saying we didn't have them and didn't see the need for buying them.


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## Highsider

All good advice until the finished drilled hole
 is a large enough diameter that you just can't push it through the material you're working with without a pilot hole.


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## mikey

Highsider said:


> All good advice until the finished drilled hole
> is a large enough diameter that you just can't push it through the material you're working with without a pilot hole.



True, true.


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## Downunder Bob

These spotting drills that you speak of are a mystery to me, I don't believe I've ever heard of them before, never seen one, and certainly never used one. When I did my apprenticeship in the early 60's we were taught to pick up a center spot with a center drill, but only drill the point in, do not drill deep enough to start the 60deg taper for running a center in. the drill with a number of drills getting larger each time up to 1/64th smaller than the required hole, then finish the hole with an on size drill with the corners slightly knocked off. only using a reamer if super accuracy was required. Larger holes requiring high accuracy were normally bored anyway. Thus pilot holes were all the go. most of our work was in annealed tool steel, maybe something to do with it. I don't remember any problems with chatter or out of round holes.


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## Bob Korves

bobshobby said:


> These spotting drills that you speak of are a mystery to me, I don't believe I've ever heard of them before, never seen one, and certainly never used one. When I did my apprenticeship in the early 60's we were taught to pick up a center spot with a center drill, but only drill the point in, do not drill deep enough to start the 60deg taper for running a center in. the drill with a number of drills getting larger each time up to 1/64th smaller than the required hole, then finish the hole with an on size drill with the corners slightly knocked off. only using a reamer if super accuracy was required. Larger holes requiring high accuracy were normally bored anyway. Thus pilot holes were all the go. most of our work was in annealed tool steel, maybe something to do with it. I don't remember any problems with chatter or out of round holes.


I very rarely have any trouble with drilling holes when using a mill or a lathe, and I imagine that other rigid machines would be about the same.  Almost all the troubles I have ever had in drilling have been hand held or on my 17" floor model Enco drill press.  If I do things the correct way, without cheating to save time, it works fine.  If I get lazy, then occasionally I have real trouble, sometimes making nasty holes and occasionally ruining an otherwise nice part.  I think the fact that this thread is now up to 44 posts says that others might have also had issues with drilling "simple" round holes to the correct size and in the correct location.  It is great that we can all learn and share on these forums...


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## grzdomagala

Spotting drills may by useful on small mills with round column. Spotting drill is shorter than standard drill but longer than center drill - maybe not much but sometimes enough to let you use standard drill or reamer without moving the table and loosing position after spotting.


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## David S

Well I have been doing quite a bit of drilling, tapping and relocating holes accurately.  Sizes are for 4-40 and 6-32 cap screws.
I am drilling and milling on my tricked out JET drill press.  Using the #5 centre drill tip only has worked extremely well.  The bit seems to snug right in without any wobble or digging in.

As a hobbyist I have been using centre drills for spotting for over 40 years.  So far my take is that with my equipment the spotting drill or in this case the tip of the large centre drill is a lot better...so far.

And this is a bit of an aside, but I also learned on this great forum the difference between spiral point and spiral flute taps and have been using the spiral point on this project in aluminum.  What a huge difference compared with straight flute.  Just cuts right through with no having to back up and break the chips.

David


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## mikey

David S said:


> Well I have been doing quite a bit of drilling, tapping and relocating holes accurately.  Sizes are for 4-40 and 6-32 cap screws.
> I am drilling and milling on my tricked out JET drill press.  Using the #5 centre drill tip only has worked extremely well.  The bit seems to snug right in without any wobble or digging in.
> 
> As a hobbyist I have been using centre drills for spotting for over 40 years.  So far my take is that with my equipment the spotting drill or in this case the tip of the large centre drill is a lot better...so far.
> 
> And this is a bit of an aside, but I also learned on this great forum the difference between spiral point and spiral flute taps and have been using the spiral point on this project in aluminum.  What a huge difference compared with straight flute.  Just cuts right through with no having to back up and break the chips.
> 
> David



I like form taps in aluminum - stronger, cleaner threads and NO chips.


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## mikey

I've been thinking about this subject and I think it comes down to this: use what works for you. You can use a center drill, spotting drill or just the drill. I don't think anyone is saying you *have* to use only a spotting drill to drill a hole, or that using a center drill is wrong. I suspect all of us are capable of testing these drills for ourselves and coming to our own conclusions. 

The value of this thread is that we have been able to share what a spotting drill is, what it is used for and how to choose one.


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## EmilioG

My collection of center and spot drills ranging in size and point angles. 60 to 150°.
I will keep testing different methods with various metals. The HiRoc is 135° for hard steels.


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## Bob Korves

I recently bought some USA made cobalt, 135 degree, split point, screw machine (stub) length drills.  Got a dozen each of 1/4 and 3/8" diameters, new and in the original sealed packaging, for less than $1 each, free shipping on eBay.  I have given some away to my buddies, but I probably still have a lifetime supply of them on hand.  I can use these as spotting drills, and they are split point so they do not need a center punch mark when using them on the mill with 90 degree smooth surfaces.  I can also use them to start holes accurately in work on the lathe.  The split points are also very useful on small center punch marks, even for hand held drill motors.


----------



## brino

Bob Korves said:


> I recently bought some USA made cobalt, 135 degree, split point, screw machine (stub) length drills. Got a dozen each of 1/4 and 3/8" diameters, new and in the original sealed packaging, for less than $1 each, free shipping on eBay.



Bob, would you have a link to that supplier?
Thanks,
-brino
Of course, not likely free shipping to Canada.....


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## Bob Korves

brino said:


> Bob, would you have a link to that supplier?
> Thanks,
> -brino
> Of course, not likely free shipping to Canada.....


Here ya' go!
http://www.ebay.com/sch/kramerkramer02/m.html?_nkw=&_armrs=1&_ipg=&_from=
He doesn't have as much stuff as he had then, but does have the 1/4" cobalt drills now selling at a little over $1 each in qty. of 12, and also a bit of freight.  Better hurry, other H-M'rs will beat you to them...


----------



## Bob Korves

Gone...


----------



## brino

Bob Korves said:


> Gone...



I guess I shoulda asked in a PM! 

Nah, I hope you fellow H-M'ers enjoy them in good health! 

-brino


----------



## Bob Korves

brino said:


> I guess I shoulda asked in a PM!
> 
> Nah, I hope you fellow H-M'ers enjoy them in good health!
> 
> -brino


I probably should have PM'd you, Brino.    PM me your address and I will send you a few...


----------



## tcarrington

been using stub drills in medium and small mills for a while now and it works amazingly well. Saves time and makes a better hole. Good advice all around.


----------



## cmantunes

Stefan Gotteswinter has a video in which he discusses center and spotting drills. Worth watching, IMO.


----------



## Nogoingback

Very interesting thread.  Like darkzero, I found some conflicting information when I looked into this as well.  I just remembered where:  www.guhring.com/documents/catalog/drills/ncspotdrills.pdf
Guhring specifically states that with HSS the spotting point angle should be less that the drill angle.  But, as Bob suggests I'm going to buy a 120 degree spotter and compare with the 90 degree that I bought
before.   I wonder if Guhring's advice assumes a CNC environment, where rigidity and accuracy is a given.  Probably not aimed at folks with floppy old drill presses.


----------



## brino

Bob Korves said:


> I probably should have PM'd you, Brino.  PM me your address and I will send you a few...



No worries Bob, I'll keep an eye out at my local used tool shop and I'm sure I can find some.
Thanks for the considerate offer!

-brino


----------



## mikey

Nogoingback said:


> Very interesting thread.  Like darkzero, I found some conflicting information when I looked into this as well.  I just remembered where:  www.guhring.com/documents/catalog/drills/ncspotdrills.pdf
> Guhring specifically states that with HSS the spotting point angle should be less that the drill angle.  But, as Bob suggests I'm going to buy a 120 degree spotter and compare with the 90 degree that I bought
> before.   I wonder if Guhring's advice assumes a CNC environment, where rigidity and accuracy is a given.  Probably not aimed at folks with floppy old drill presses.



Back when I tested these drills (can't even remember how long ago that was), I used a 1/8" drill bit. I tested them because I noticed that my smaller drills were not drilling where I wanted them to when I spotted with the 90 degree spotter. I also noted that a freshly sharpened drill was not outputting equal-sized chips, which suggested to me that the edges were being dulled or damaged somehow. At the time, I didn't even know that there were other angles available in spotting drills but when I looked, I saw that a 120 degree drill was available so I ordered one and all the issues went away. 

Were it not for the fact that I was trying to fit a part to another part that required the holes to line up precisely (I was building a precision square) I may never have stumbled upon the difference between these spotting drills. 

My point is that when using larger non-carbide drills with greater inherent stiffness and less fragile edges, a 90 degree spotting drill may be fine. For myself, I prefer a 120 but admit that I are a bit anal about it.


----------



## Randall Marx

This long and interesting discussion has piqued a question: how well or how poorly would a 118 degree drill center in a hole spotted with a 140 degree spotting drill? I ask because I do not own any spotting drills. I've used just the tip on center drills to locate holes for 118 degree drills. That worked very well. I now have 135 degree cobalt split-point drills AND 118 degree drills. I'm considering getting some 140 degree spotting drills to use with the cobalt drills and wonder if I can safely and effectively use the same spotting drills for my 118 degree drills. If not, I might get some 120 degree spotting drills to use with the 118 degree drills and keep the spotting drills with their respective drills in the indexes (120 with 118's and 140 with 135's). If the 140's will work as well with the 118 degree drills, that is less to buy and track.
Thanks!


----------



## Bob Korves

Randall Marx said:


> This long and interesting discussion has piqued a question: how well or how poorly would a 118 degree drill center in a hole spotted with a 140 degree spotting drill? I ask because I do not own any spotting drills. I've used just the tip on center drills to locate holes for 118 degree drills. That worked very well. I now have 135 degree cobalt split-point drills AND 118 degree drills. I'm considering getting some 140 degree spotting drills to use with the cobalt drills and wonder if I can safely and effectively use the same spotting drills for my 118 degree drills. If not, I might get some 120 degree spotting drills to use with the 118 degree drills and keep the spotting drills with their respective drills in the indexes (120 with 118's and 140 with 135's). If the 140's will work as well with the 118 degree drills, that is less to buy and track.
> Thanks!


I have not tried it, but I expect that the 140 degree starter drill followed by a 118 degree main drill would work just fine, probably no different than following a 120 degree starter drill.  As long as the main drill has a smaller angle than the starter drill, the drill should center in the cone.  I love the 135 degree split point cobalt drills, especially the machine screw (stub) length.  If you are square to a smooth surface with them, you can pretty much forget about starter drills if you are using a drill press or a mill.  I also have some of the jobber length ones as well, and they work almost, but not quite as well without a starter drill.


----------



## Scruffy

I quit using center drills for spotting when I broke the tip off one and spent an hour getting the broken piece out! I have bought sets of lettered, numbered and fractional in stub length and love them.
Posted from the osu heart center in Columbus Ohio. My 84 year old father had a bad episode Friday morning. This is night numer 2 for me , got one and a half hours sleep last night sure hope tonight is better.
Thanks scruffy
Update my father just asked me if I had a pocket knife? His iv line had got tangled and he wanted me to cut it. Gonna be a long night.


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## EmilioG

The 140° to 150° spot drills will work for (me), on any drill below those included angles; 118, 135.   With my 8mm Guhring 142 carbide spot drill, I can make the spot shallow or wider/deeper, depending on the drill size up to about 5/16".  For small holes, I'll use a 1/4" spot drill.  If the holes I need are not deep, I mostly use stub length drills.

Tom Griffin told me that he doesn't even bother with spots, he just pecks a spot with the final drill and goes.
I use spot drills most of the time, especially with smaller size drill bits or on round parts.  I may start using a sharp conical point to find my punch marks.
I have used a Starrett wiggler and the conical point on a Starrett double end edge finder with some success.  Hitting a target hole on center w/o a DRO is a challenge.
But I like a good challenge, so I keep drilling.  I just have to take my time, I don't want to ruin the parts I'm working on.


----------



## Randall Marx

Thanks for the input everyone. Sounds like the consensus is that it should work for me to use one set of wide-angle spot drills for all of my drills. I plan to order some with my next tooling order. If anyone has a GOOD reason not to use the 140 degree spotters with 118 degree drills, please speak up. Otherwise, I'll get some.
Thanks again.


----------



## EmilioG

The 140° will work with all drills under 140, but I would also test the matched examples, 120 spot with 118, 140 spot with 135.


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## Ken from ontario

Excuse my ignorance please,I didn't know much about spot drills, but what does it mean when they say :
APPLICATIONS
Chamfers and centers in one operation.
Does that mean you can chamfer with these little drill bits?

http://www.traverscanada.com/solid-carbide-90176-nc-spot-drills/p/381607/?keyword=spot+drill


----------



## darkzero

Ken from ontario said:


> Excuse my ignorance please,I didn't know much about spot drills, but what does it mean when they say :
> APPLICATIONS
> Chamfers and centers in one operation.
> Does that mean you can chamfer with these little drill bits?
> 
> http://www.traverscanada.com/solid-carbide-90176-nc-spot-drills/p/381607/?keyword=spot+drill



See the last paragraph in post #16


----------



## Mutt

mikey said:


> I totally forgot to add that when choosing a spotting drill, it only has to be big enough to span the web of the main drill. A 1/4" spotting drill will work for most drills in your drawer up to and including 1/2". If your drills are 118 degree points, use a 120 degree spotting drill. If using 135 degree split points, a 140 degree spotting drill works.




 the 140º spot drills are near impossible to find, but 135º drill bits are EVERYWHERE.  Companies  act like it is a major job to grind the spot drill to 140º instead of 120º ???????????????????????????  Seems to me, if I were in the drill bit making business, I would be offering the 140º spot drill before a 120º as both 118 and 135 drills would work using it, but not visa-versa. Besides, what happened to companies making what people want, instead of making what they think customers need?????????

After reading an article on this and buying a couple of spot drills, the concentricity of the holes  being drilled on my lathe have improved immensely


----------



## mikey

Yup, 140 degree spotting drills are harder to find but they have a bunch on ebay and Amazon usually has some. They sort of last forever; I'm still using a 120 degree spotter that is old, not sure how old, but its still sharp. I have maybe 5 more as a backup but haven't had to pull one out. I buy cobalt spotters, not carbide, because if I drop it then it is more likely to survive the drop.


----------



## T Bredehoft

Bob Korves said:


> If you ask 10 machinists at random, most will say that the advice in this thread is all wrong



Sometimes traditions were developed before technology interfered.  The stubby screw machine drills took a long time to migrate to machinist's tool boxes.


----------



## David S

Well all I can say is that I would vote this "tip of the year".  I have noticed improvements in the past few weeks since I started using them.

David


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## Jimsehr

If the angle is not what you want grab a protractor and hit the grinding wheel.
Jimsehr


----------



## EmilioG

I have a Guhring 142° spot drill.  I have a few Guhring 140° drills carbide, so I needed one. Guhring recommends using 90° spot drills with non carbide drills.
The 90 degree spot used looks like a size to just fit the chisel point of the follow drill.  Guhring now makes spot drills in cobalt bright.  Msc has a pretty good selection, even 145°.  
see>>   http://www.guhring.com/Documents/Catalog/Drills/NCSpotDrills.pdf


----------



## Splat

FWIW,  McMaster-Carr has all different angled, including 140º, spotting drills.


----------



## Wreck™Wreck

wildo said:


> Oh good! I'm glad to know that I didn't get the "wrong" center drills since my primary application is indeed starting holes on the lathe (or maybe in the mill). I guess I'm still a little confused about the purpose or point of the spotting drill, but I think this might be in definition alone. If I had to take a guess at what "spotting" a hole means, I'd imagine it meant to start the hole in the correct location. IF that's true, one could claim (maybe?) that a center drill is a specialized type of spotting drill since it is also used for starting the hole in the correct location, namely- the center of spinning stock. Am I on track here?
> 
> If all that's true, then I'd infer that a center drill is for starting a hole specifically on a lathe, and a spotting drill is for starting a hole everywhere else. Yes?


Unless you are in a production environment any method of spotting a hole is valid, there is no right or wrong way there is only a faster or slower way.

Let us use a bit, no pun intended, of reason, lathe centers are typically 60 degrees so a Center drill is 60 degrees with a pilot diameter that ensures that the sharp point of the center does not reach the bottom of the hole. When spotting a drill location the pilot diameter is not in any way useful.  A center drill is used to create work holding features.
Why do many taps have centers in each end? They are not there to make your life easier, they are there because this is how the manufacturer holds them, small taps are often sharply pointed ends where the point is held with an external center when being ground.

Spotting drills are often 90 degrees included angle which will create a 45 Degree chamfer on the hole entrance which will require no deburring afterwards, this in itself is an advantage.
They are less easily broken then center drills.
The angles are better when followed by a twist drill, this  may help answer your original question. As a hobbyist are you drilling 10 holes per day or 1000 holes per day? 
If only several holes per project use whatever method works for you and your equipment as this is what is the "right" method. Ignore most of the "How To Do This Correctly" web advice, for many people the exercise of thinking about a process is more important then actually doing it.


----------



## EmilioG

I did find spot drills smaller than .250"  Msc has Keo and MA Ford spot drills in 140° and 142° bright, solid carbide, not expensive, down to 1/8"
The Guhring spot drills are very expensive. I have one that was sent to me as a sample.  MA Ford also has spot drills in their Hi Roc line for hard steels in 145°, down to 3mm.
These spot drills are very short and rigid. I prefer cobalt, but these carbide spotters should work nicely.


----------



## Downunder Bob

Bob Korves said:


> I really prefer to use no starter drill, just a 135 degree split point screw machine (stub) length drill which is stiffer, will not walk on the work, and will center itself.  Starter drills are a major waste of time.


And money.


----------



## Jimsehr

David S said:


> Lots of good information here, thank you.
> Now I am looking for affordable spotting drills and find that 90 degrees seems to be very popular.
> 
> When would one use a 90 degree spotting drill?
> 
> David


----------



## Jimsehr

David S said:


> Lots of good information here, thank you.
> Now I am looking for affordable spotting drills and find that 90 degrees seems to be very popular.
> 
> When would one use a 90 degree spotting drill?
> 
> David


You use a 90 degree spot drill when you want to put a 45 degree chamfer on the part and also use drill as a starter.


----------



## David S

Thanks Jim,

I came across that explanation after I had posted way back when.  For the normal spotting I make sure the "dimple" is smaller than the diameter of the follow up bit.  For chamfering it would be larger than the follow up drill bit.  Saves an extra step.  I like it.

David


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## Scruffy

1st time you break the tip Off a centering drill in a piece and spend hours trying to save the piece  you will think ,theirs gott’a be a better way.
Only screw machine or spot drills for me.
Thanks Ron


----------



## Bob Korves

Jimsehr said:


> You use a 90 degree spot drill when you want to put a 45 degree chamfer on the part and also use drill as a starter.


That idea can save time.  It can also cause an ugly hole.  Think carefully about a 118 or 135 degree drill coming down to intersect the oversize 90 degree cone left by the chamfering tool.  The first points of contact (impact!) will be made by the outside corners of the drill's cutting edges.  The first corner that makes contact deflects the drill, which causes the second corner to hit even harder, and this increases to whatever flex the drill is capable of under the load.  The drill walks around the hole, making lobes, often in a triangular pattern.  The drilling machine shakes at high speed and amplitude.  It ain't pretty.  The drill is often damaged.  And I have been there, more times than I would like to admit.  It mostly happened on my 17" floor model drill press, which is much less rigid than my mill.  It ruins the work or leaves it ugly for all to see.  Having a flatter cone than the following drill makes the drill start at the center of the hole and then gradually open up the hole at a larger cone angle than the starting drill had.  I might attempt the chamfer first idea when using a rigid mill and setup, while cutting something like soft aluminum, otherwise I would not try it at all.  Too many personal experiences with failure...


----------



## David S

Scruffy said:


> 1st time you break the tip Off a centering drill in a piece and spend hours trying to save the piece  you will think ,theirs gott’a be a better way.
> Only screw machine or spot drills for me.
> Thanks Ron



Indeed,  I have a incomplete selection of stub bits and use them whenever I can.  And consider that they are about 8 times stiffer than jobber length bits.

David


----------



## petertha

Interesting stuff here. I threw together some sketches of different combinations of spot/center hole angle & typical 118-deg twist drill angle, deep/shallow etc.  I too have been guilty of the classic 60-deg center drill, having been instructed that way. After watching some of my drills drift away or worse yet grab in softer alloys, it was time to ponder. Hopefully pics help illustrate words of what might be going on. I figure the trouble-maker is the point contact (red arrow) with wide relief gap on either side. It doesn't seem to matter much (visually) whether spot drill is shallow or deep, its a similar issue on a different point of the drill. A 90-deg spot hole is a bit of improvement over 60-deg, but not hugely. I'm sure there is more to the story in reality - different hardness, chip forming etc. But this kind of makes sense to my amateur eye.

With a spot hole angle slightly larger than drill angle (120 vs 118 deg respectively), there is still theoretical 'point' contact, but now a very teeny, shallow relief angle between them which allows for a nice contact start & then true centering as the drill progresses. At least that's my own personal conclusion. 

The only thing I wonder about is a combo 118 center & 118 drill. Yes the angles match so its like a cone within a cone, but now the entire cutting edge of the drill contacts hole simultaneously. To me this is like putting an extra wide cutter or form tool in the lathe. You need more power & rigidity, but also more friction, heat & chatter potential vs. a smaller cutting contact area. Maybe now we are splitting gnat hairs. Who knows, my 118 drills could be 117 or 119 or any run-out will start cutting on one face first anyway. I only have a mish-mash of 118 centers but generally & the improvement in hole making was noticeable. But I think I'm convincing myself to get a progressive series of 120-deg spot drills.


----------



## Bob Korves

petertha said:


> It doesn't seem to matter much (visually) whether spot drill is shallow or deep, its a similar issue on a different point of the drill.


Look at where the red arrows intersect the drill in your illustrations.  The farther out on the drill cutting edge where initial contact is made, the more leverage there is to start the drill walking around the cone.



petertha said:


> The only thing I wonder about is a combo 118 center & 118 drill. Yes the angles match so its like a cone within a cone, but now the entire edge of the drill contacts hole simultaneously. To me this is like putting an extra wide cutter or form tool in the lathe. You need more power & rigidity, but also more friction & heat vs. a smaller contact area. Maybe now we are splitting gnat hairs. Who knows, my 118 drills could be 117 or 119 or any run-out will start cutting on one face first anyway. I only have a mish-mash of 118 centers but generally & the improvement in hole making was noticeable. But I think I'm convincing myself to get a progressive series of 120-deg.


Then you are in an unstable situation, where it might go well if the entire drill (or just the center) contacts first, but might also go very wrong if by chance one side of the drill first catches at the O.D. of the hole while the opposite side makes contact near the center of the hole or with no contact at all.  The drill is most likely to have a successful start with a starting hole angle enough larger than the drill angle so that there would be no chance of the outer portions of the drill making first contact with the work.  Using a starter hole just over the size of the drill chisel point would achieve the same thing, and would also reduce wear and time on the starter drill.


----------



## brino

petertha said:


> Interesting stuff here. I threw together some sketches of different combinations of spot/center hole angle & typical 118-deg twist drill angle, deep/shallow etc.



@petertha, that is exactly the series of pictures I have in my head from my experiences at the drill press.....but I've never sat down and drawn them out.



petertha said:


> he only thing I wonder about is a combo 118 center & 118 drill. Yes the angles match so its like a cone within a cone, but now the entire edge of the drill contacts hole simultaneously. To me this is like putting an extra wide cutter or form tool in the lathe. You need more power & rigidity, but also more friction & heat vs. a smaller contact area. Maybe now we are splitting gnat hairs.



I understand what you mean about presenting the wider tool face to the work. Typically this is worse for lathe work.
However, in this case I believe it is orders of magnitude better than the deflection that would be caused by using the "shallower" starter drill.

Thanks for sharing your thoughts and pictures, it is greatly appreciated!

-brino


----------



## Bob Korves

OK, let's look at it a bit differently.  I drill a 7/16" hole in steel on the drill press.  Then I decide to open it up to 1/2".  The odds are very good that the drill will walk and make an ugly oversize lobed hole while everything shakes badly.  There is no cure at that point beyond starting over.  I have had this happen many times doing fabrication work.  I think the drill is "walking" around the hole.  If I make a center punch hole or a starter drill hole a little larger than the chisel point of the drill, I always get a clean hole, no exceptions.  Slow or fast starting feeds make no differences.  Tell me what you think is causing this scenario.


----------



## Scruffy

I agree with wreck unles your doing a thousand it doesn’t matter. I don’t think anyone on this forum is working for nasa.
Ron


----------



## petertha

You're right Bob. Thus far the discussion has been about how best to center a drill relative to a preceding angled spotting pilot hole. But when opening up a hole with progressively larger drills, the 118-deg tip now sees a 90-deg corner from the prior hole as its first point of contact. Out of habit I just kiss that edge or peck a bit until it gets started. But I don't see any other way around this using drills.


----------



## Bob Korves

petertha said:


> You're right Bob. Thus far the discussion has been about how best to center a drill relative to a preceding angled spotting pilot hole. But when opening up a hole with progressively larger drills, the 118-deg tip now sees a 90-deg corner from the prior hole as its first point of contact. Out of habit I just kiss that edge or peck a bit until it gets started. But I don't see any other way around this using drills.


The way around it is to never get into the situation that I described, getting into trouble with enlarging a hole without solid support for the drill.  And enlarging a cone is enlarging a hole, same issue, maybe worse, because of the wider chunk a flute can grab on first contact and musch less initial support.  The answer is to start in the center of the hole, forming a small cone, and then moving gradually deeper and outward to a bigger hole with enough central cone contact to support the cutting forces as the hole enlarges.  That is how I see it, anyway, and it works for me.


----------



## Downunder Bob

I was taught as a tool making apprentice to start with a center drill selecting one where the chisel point of the drill was as close as possible to the dia of the starting point of the center drill and do not drill down to the 60 deg section, thus the following drll would not wander. This what we always did in the tool room where I was. I have always used this method ever since, and it has never let me down. 

I don't recall hearing the term spotting drill in this sense until joining this forum. A spotting drill to us was also known as a step drill for drilling counter bores for SHCS using a pilot to set it true to the original hole, can also be used to spot a face around a hole in a casting or where the surface is not flat or square to the hole.


----------



## EmilioG

Bob Korves said:


> OK, let's look at it a bit differently.  I drill a 7/16" hole in steel on the drill press.  Then I decide to open it up to 1/2".  The odds are very good that the drill will walk and make an ugly oversize lobed hole while everything shakes badly.  There is no cure at that point beyond starting over.  I have had this happen many times doing fabrication work.  I think the drill is "walking" around the hole.  If I make a center punch hole or a starter drill hole a little larger than the chisel point of the drill, I always get a clean hole, no exceptions.  Slow or fast starting feeds make no differences.  Tell me what you think is causing this scenario.



Would using a 1/2" end mill work? Center cutting of course.


----------



## mikey

Downunder Bob said:


> I was taught as a tool making apprentice to start with a center drill selecting one where the chisel point of the drill was as close as possible to the dia of the starting point of the center drill and do not drill down to the 60 deg section, thus the following drll would not wander. This what we always did in the tool room where I was. I have always used this method ever since, and it has never let me down.



I believe this is what Bob K. suggested earlier but the guys lightheartedly gave him grief for not mentioning it until after they already ordered/bought their spotters but I agree with you - it works.


----------



## Bob Korves

Downunder Bob said:


> I was taught as a tool making apprentice to start with a center drill selecting one where the chisel point of the drill was as close as possible to the dia of the starting point of the center drill and do not drill down to the 60 deg section, thus the following drll would not wander.


As Mikey says, that is an OK approach, the center drill is quite stiff, but the secret is more than not drilling down to the 60 degree section, it is in not drilling down to the parallel section, just use the 120 degree point of the center drill, and do not allow any of the parallel portion of the center drill to enter the work.  Now we have a spot accurately located by a stiff starting drill, and with a small cone a 118 degree drill can follow faithfully.


----------



## petertha

Bob Korves said:


> The answer is to start in the center of the hole, forming a small cone, and then moving gradually deeper and outward to a bigger hole with enough central cone contact to support the cutting forces as the hole enlarges.  That is how I see it, anyway, and it works for me.



If I understand, you mean do the progressive enlarged drill stepping just at the beginning of the hole & then plunge all the way with the biggest size? If so, that would require a lot of in-feed force for the final drill, at least for my equipment. For example my cylinder liners ~ 1" bore x 2" long. No way I could push say a 5/8" or 3/4" drill through steel in one go. Even with a 3/8" drill the material wanted to slide back in the chuck jaws, so I turned a small step that butts against the front of jaws & do the operation blind hole. Actually I consider 'drilling' as a roughing operation just to min ID for my boring bar. I'm less concerned by hole quality than the drill cone catching on the bore of the prior drill & walking off center. But aside from using an annular cutter from both sides & go straight to boring bar, I see no other option.

How the h*ll do they drill long gun barrels anyway? :/


----------



## mikey

petertha said:


> If I understand, you mean do the progressive enlarged drill stepping just at the beginning of the hole & then plunge all the way with the biggest size? If so, that would require a lot of in-feed force for the final drill, at least for my equipment. For example my cylinder liners ~ 1" bore x 2" long. No way I could push say a 5/8" or 3/4" drill through steel in one go. Even with a 3/8" drill the material wanted to slide back in the chuck jaws, so I turned a small step that butts against the front of jaws & do the operation blind hole. Actually I consider 'drilling' as a roughing operation just to min ID for my boring bar. I'm less concerned by hole quality than the drill cone catching on the bore of the prior drill & walking off center. But aside from using an annular cutter from both sides & go straight to boring bar, I see no other option.
> 
> How the h*ll do they drill long gun barrels anyway? :/



I probably do it wrong but when I need to make a precision hole, like your cylinder liners, I spot and then drill with the biggest drill I can use without step drilling. This gives me zero chatter and the best chance at a fairly clean, straight-ish hole. Then I bore it from there. Sometimes this involves a fair amount of boring but at least I end up with a precisely sized concentric hole with straight sides and a good finish.


----------



## Downunder Bob

Let's not get carried away guys, if the hole is going to be bored the accuracy of the drilled hole is not important, it's just a starting point for the boring process. 

However if the drilled hole is the final act, then get it right the first time. Locate the hole with a center drill then drill as close to the final size as possible, within 1/64 or 0.5 mm, in one act, finish with a reamer. if a reamer is not available, then modify the finish drill by rounding the corners of the drill bit This drill will follow the existing hole and finish on size. The poor mans reamer, if done correctly it works very well.


----------



## Bill Gruby

If you want the most accurate hole using only a drill I would  use a spot drill and not a center drill. Center drills are for spotting a work piece for a lathe center. This is my thoughts here. Others may differ.

 "Billy G"


----------



## David S

Bill Gruby said:


> If you want the most accurate hole using only a drill I would  use a spot drill and not a center drill. Center drills are for spotting a work piece for a lathe center. This is my thoughts here. Others may differ.
> 
> "Billy G"



For decades I used the centre / countersink drill for starting, but a while back with info from this great site switched to spotting drills and I got an immediate and noticeable improvement.  Huge improvement.

So I fully agree Billy G

David


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## petertha

I know drilling thin metal isn't the same as thicker stock, but the small increment 'progressive' type drilling seem to rely on this principle to make good circular holes. Mind you, I've also wondered if what also helps make these work has as much to do with a preferable rake angle vs. regular twist drills even if you tried to mimic with the same series of drill sizes.


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## EmilioG

Using the tip of a center drill/Csnk. isn't a bad idea if you're using 118° drill bits.  I found 145° spotting drills in a range of sizes from MA Ford.
They make them all the way down to 3mm/1/8".  I'll use them with my 135-140° drills.


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## Downunder Bob

mikey said:


> I believe this is what Bob K. suggested earlier but the guys lightheartedly gave him grief for not mentioning it until after they already ordered/bought their spotters but I agree with you - it works.



The guys are amusing, don't get me wrong I love this site, One can learn so much here and, unlike some others, it is friendly What I find amusing is the way they go on about spotting drills as if it was the end of everything in the world of machining. Like i said before the only spotting drills I had ever heard of were the ones we had to make as a project as apprentices. Some people call them step drills, They are used to spot face a surface around a drilled hole, particularly on a casting, so that a bolt has a flat square surface to tigten against, I still have my set  They were also used to countersink holes for SHCS to set below the surface, My set of five drills is designed for 1/4", 5/16", 3/8", 7/16" and 1/2" SHCS. 

I can't help but think the guys have never done it tough, and had to make do with the tools at hand. Most of the machines we had when I  was an apprentice were known as "Wartime finish". which meant no time, money, or effort was used in making them look nice, sure,they worked fine and were good machines, they just looked unfinished, and that is how they stayed.

There were of course no digital instruments at all. No DRO's No CNC, every thing was done manually A few of the toolmakers had their ownn 6" or150 mm vernier calipers, most of our toolmakers were imigrants from war torn europe, out of 12 toolmakers only two were Australian born and trained, another three were from UK, and the rest came from various parts of Europe. In many ways probably the best apprenticeship a guy could have, as we were exposed to all the different engineering cultures of that time. Everyone had a 1" or 25mm mic, for larger sizes we had to get the 0 - 6" mic from the tool store, this mic had a set of changable fixed anvils that would allow it to be set up to measure all sizes from 0 to 6" I could go on, but I'm sure you get the picture


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## Bob Korves

Downunder Bob said:


> The guys are amusing, don't get me wrong I love this site, One can learn so much here and, unlike some others, it is friendly What I find amusing is the way they go on about spotting drills as if it was the end of everything in the world of machining. Like i said before the only spotting drills I had ever heard of were the ones we had to make as a project as apprentices. Some people call them step drills, They are used to spot face a surface around a drilled hole, particularly on a casting, so that a bolt has a flat square surface to tigten against, I still have my set  They were also used to countersink holes for SHCS to set below the surface, My set of five drills is designed for 1/4", 5/16", 3/8", 7/16" and 1/2" SHCS.
> 
> I can't help but think the guys have never done it tough, and had to make do with the tools at hand. Most of the machines we had when I  was an apprentice were known as "Wartime finish". which meant no time, money, or effort was used in making them look nice, sure,they worked fine and were good machines, they just looked unfinished, and that is how they stayed.
> 
> There were of course no digital instruments at all. No DRO's No CNC, every thing was done manually A few of the toolmakers had their ownn 6" or150 mm vernier calipers, most of our toolmakers were imigrants from war torn europe, out of 12 toolmakers only two were Australian born and trained, another three were from UK, and the rest came from various parts of Europe. In many ways probably the best apprenticeship a guy could have, as we were exposed to all the different engineering cultures of that time. Everyone had a 1" or 25mm mic, for larger sizes we had to get the 0 - 6" mic from the tool store, this mic had a set of changable fixed anvils that would allow it to be set up to measure all sizes from 0 to 6" I could go on, but I'm sure you get the picture


Remember, Bob, this is a FORUM where we TALK about machining.  This is not our shops.  You seem happy to tell your stories as well, and they are good ones.  Conversations on forums like this tend to gravitate toward the BEST possible solution to any project or operation.  Obviously, none of us have the tools, machines, and skills to do everything that is suggested.  The great part of our discussions, in my mind, is really thinking and digesting what we are planning and doing on a certain operation, not just doing it by rote the same way grandpa told us to.  That is how we improve our skills in a lonely home shop, with no shop foreman or coworkers to help us out.  Not all shops here are equipped the same, the hobby machinists here have widely differening mixes of skills and backgrounds, and we have a universe of different project and work flow ideas.  I think we all benefit from hearing the whole spectrum on how to drill a hole, for instance, from quickly punching a hole in a piece of scrap to creating a demanding bolt pattern as best as we can do it with our resources.  Additional skills, more ideas, and a wider outlook can do nothing but help our approaches to doing good work in our shops, in my opinion.  If readers of the posts think that means they need to buy a brand new machine and tooling for every operation they do, well, that is a personal problem.  I try to offer cheaper, quicker, and simpler approaches to doing something in my posts whenever appropriate.  This wonderful and useful forum is all about learning and sharing.  Like on any forum, we all need to separate what makes sense to us from what does not.


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## mikey

Downunder Bob said:


> The guys are amusing, don't get me wrong I love this site, One can learn so much here and, unlike some others, it is friendly What I find amusing is the way they go on about spotting drills as if it was the end of everything in the world of machining. Like i said before the only spotting drills I had ever heard of were the ones we had to make as a project as apprentices.



 I enjoyed your description of your experiences, Bob. Would that more of us had the benefit of the kind of training you got but the fact is that what you learned decades ago, many hobby guys are learning for the first time here, on HM. We are not in the trade; we are here by choice and interest and a lot of us are learning things on the net, possibly for the very first time. What you may see as the guys making a big deal about spotting drills, I see as growth and learning in a hobby guy as something is made clear for the first time. Remember that you are coming from a background in the trade, whereas most of us are skilled workers or professionals in our own fields that just happens to not be machining; this is new to many of us.

I'm just a hobby guy that has been bumbling his way along for about 30 years now. I know that it is not enough for a hobbyist to just know what. He must also know why and how and when in order to develop a skill. When someone provides that for him, a light bulb often goes off in his head and he understands. Some of the guys get excited when this happens; I get it. 

I know you get it, too, so when you can, teach us. But don't just tell us what; tell us why, how and when. You may not always see it in the posts that follow but I guarantee you that some hobby guy sitting in his shop will be smiling because you opened a door in his mind.


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## Downunder Bob

Bob Korves said:


> Remember, Bob, this is a FORUM where we TALK about machining.  This is not our shops.  You seem happy to tell your stories as well, and they are good ones.  Conversations on forums like this tend to gravitate toward the BEST possible solution to any project or operation.  Obviously, none of us have the tools, machines, and skills to do everything that is suggested.  The great part of our discussions, in my mind, is really thinking and digesting what we are planning and doing on a certain operation, not just doing it by rote the same way grandpa told us to.  That is how we improve our skills in a lonely home shop, with no shop foreman or coworkers to help us out.  Not all shops here are equipped the same, the hobby machinists here have widely differening mixes of skills and backgrounds, and we have a universe of different project and work flow ideas.  I think we all benefit from hearing the whole spectrum on how to drill a hole, for instance, from quickly punching a hole in a piece of scrap to creating a demanding bolt pattern as best as we can do it with our resources.  Additional skills, more ideas, and a wider outlook can do nothing but help our approaches to doing good work in our shops, in my opinion.  If readers of the posts think that means they need to buy a brand new machine and tooling for every operation they do, well, that is a personal problem.  I try to offer cheaper, quicker, and simpler approaches to doing something in my posts whenever appropriate.  This wonderful and useful forum is all about learning and sharing.  Like on any forum, we all need to separate what makes sense to us from what does not.



 You are quite right Bob, And I apologise to anyone and everyone who feels that I unfairly critisized them and or their way of doing things. Yes this is a forum and it is a great one at that.

My training was a long time ago 1961 -1966. I've probably forgotten much of what I learned, and I'm often frustrated by the new fangled way of doing things.

This discussion on drill points intrigues me, because I don't remember ever using a drill with a 135deg point, in fact I don't recall ever seeing one for sale or anywhere else. I have only ever used 118 deg drill bits often with the point split, or partially split.  Occasionlly I will sharpen a drill in a different way say for drilling sheet metal or brass. I will also round the shoulders on a drill when I need a very accurate hole that cant conveniently be bored. Drilling the hole to 1/64th or 0.5mm or less if possible undersize then follow through with the on size drill with rounded shoulders will act like a reamer, giving a clean hole that is on size.

When the location is importand I've always started my drilled holes with a center drill. I believe a correctly sharpened drill will drill straight and pretty close to on size once it is started like this.


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## Downunder Bob

mikey said:


> I enjoyed your description of your experiences, Bob. Would that more of us had the benefit of the kind of training you got but the fact is that what you learned decades ago, many hobby guys are learning for the first time here, on HM. We are not in the trade; we are here by choice and interest and a lot of us are learning things on the net, possibly for the very first time. What you may see as the guys making a big deal about spotting drills, I see as growth and learning in a hobby guy as something is made clear for the first time. Remember that you are coming from a background in the trade, whereas most of us are skilled workers or professionals in our own fields that just happens to not be machining; this is new to many of us.
> 
> I'm just a hobby guy that has been bumbling his way along for about 30 years now. I know that it is not enough for a hobbyist to just know what. He must also know why and how and when in order to develop a skill. When someone provides that for him, a light bulb often goes off in his head and he understands. Some of the guys get excited when this happens; I get it.
> 
> I know you get it, too, so when you can, teach us. But don't just tell us what; tell us why, how and when. You may not always see it in the posts that follow but I guarantee you that some hobby guy sitting in his shop will be smiling because you opened a door in his mind.



Thanks Mikey, I will try to accept the position of teacher, although I think there are many here who do a better job of that than I could ever do. I don't have the patience, I find as I'm running out of time, and far too many things to do. My other half has been very unwell these last 14 months, so I spent very little time in my shop, although she is now on the mend and recovering well, so hopefully more shop time coming up.

I will continue to add my ten cents to any discussion that I think I can offer something too. I will also try to be  alittle less blunt.


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## mikey

Downunder Bob said:


> Thanks Mikey, I will try to accept the position of teacher, although I think there are many here who do a better job of that than I could ever do. I don't have the patience, I find as I'm running out of time, and far too many things to do. My other half has been very unwell these last 14 months, so I spent very little time in my shop, although she is now on the mend and recovering well, so hopefully more shop time coming up.
> 
> I will continue to add my ten cents to any discussion that I think I can offer something too. I will also try to be  alittle less blunt.



Sorry to hear about your spouse and I hope things continue to go well.

Bob, you weren't blunt or critical. You have a different perspective than us hobby guys and I think we all respect that; I just wanted to share from the other side of things, that's all. We're glad to have you on HM and look forward to whatever you have to share.


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## woodchucker

This disagrees with some of the info shared here.  Source: http://www.guhring.com/Documents/Catalog/Drills/NCSpotDrills.pdf

If using a HSS or HSCO drill, choose a spot drill with a smaller point angle (i.e. spot with a 90° drill, follow with a 130° drill)

For a carbide drill, choose a spot drill with a larger point angle (i.e. spot with a 142° drill, follow with a 140° carbide drill)

Thought I would post it, as I am always forgetting the rule. I do like spotting drills on some tough to center , tough to line up holes.


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## Mitch Alsup

So, this thread advocates going directly to the size of hole you want without drilling smaller sizes out first.
What is the backup plan if your lathe/drill press/mill does not have enough power to drill the hole in one step?


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## Bob Korves

woodchucker said:


> This disagrees with some of the info shared here. Source: http://www.guhring.com/Documents/Catalog/Drills/NCSpotDrills.pdf


Jeff, you will find many opinions and directions for drilling holes, in this thread and elsewhere.  Many will contradict 180 degrees from each other, and all will be touted as gospel by someone on the worksite or posting in the thread.  Ultimately, you will make the call on how to proceed in your home shop.  Consider the options, and visualize the mechanics of how each of them works, and how they might or might not improve workflow and accuracy in your shop.  Try a few ideas and see what seems best for you.  Go with it, but remember that there are lot of other ideas that might work best for drilling your next hole.


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## petertha

Bob, that's the conclusion I'm arriving at in my own amateurish way. I have conventional 60-deg center drills plus 90, 118 & 120 deg spotting drills in my collection. I've been randomly trying different ones in different materials, just as I'm going about machining my parts.  My drills are typical 118 point HSS. If I watch the drill very carefully just as its entering the pilot, a 'general' observation is the shallower angle centers will on average have a higher chance of grabbing & displacing the bit over a smidge. Not always, not necessarily the same amount, but on average. What it does for the next 1mm into the hole seems to be a function of drill size, material, speed... all that stuff. Sometimes it will straighten itself out, sometimes I just have to assume its a slightly deviated hole. 

The higher angled spotters generally seem to be less of this, all things equal. Again very unscientific. So theory says 118 spotter should be better than 120 but I'm having trouble seeing anything significantly different between them. In fact, almost tending towards 120. Which is maybe good news because 118's seem to be harder to source, so I probably wouldn't re-buy them again. 

In terms of the question about power demands going to the big drill right up front vs. progression drilling, totally point valid IMO on many hobby sized machines. Possibly an annular cutter but that doesn't work for blind holes & has depth limits under say 2". I have a 14x40 lathe which has decent power, but I've ran into other issues just gripping the part in the chuck with the axial load without excessive gronking. And teh tailstock sliding back which I think I've solved. So progression drilling is about the only compromise I can see. I treat drilling as a roughing operation anyway, basically the unnecessary evil to make room for a boring bar - LOL

On another note, I had to make some deeper counter-bores for M10 cap screws. I don't have a proper tool that does this, but I sunk in a fine tooth roughing end mill & was amazed at how effortless it was to open up the hole. It had a pilot hole for the bolt shank of course & that may have helped things. the end mil was short & rigid. I'm not sure if  this is 'proper' machining but it worked well in this application.


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## woodchucker

Bob Korves said:


> Jeff, you will find many opinions and directions for drilling holes, in this thread and elsewhere.  Many will contradict 180 degrees from each other, and all will be touted as gospel by someone on the worksite or posting in the thread.  Ultimately, you will make the call on how to proceed in your home shop.  Consider the options, and visualize the mechanics of how each of them works, and how they might or might not improve workflow and accuracy in your shop.  Try a few ideas and see what seems best for you.  Go with it, but remember that there are lot of other ideas that might work best for drilling your next hole.



I agree, I just thought I would present their knowledge base on the subject. A little stirring the pot, seems like we are low on the discussions these days.


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## Bob Korves

woodchucker said:


> I agree, I just thought I would present their knowledge base on the subject. A little stirring the pot, seems like we are low on the discussions these days.


It would have been more interesting if Guhring talked about the "why" of their recommendations.


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## Bob Korves

Mitch Alsup said:


> So, this thread advocates going directly to the size of hole you want without drilling smaller sizes out first.
> What is the backup plan if your lathe/drill press/mill does not have enough power to drill the hole in one step?


Finishing a hole with a boring bar is the best idea for making a hole that ends up placed where you want it, and is also a way to open up smaller drilled holes while gaining accuracy, not losing accuracy.  It does not save time, however.  I have never done boring on a drill press, don't really have a setup put together that would do that, but boring holes sure works great on the lathe and on the mill.  Taking the last few thousandths with a reamer of the correct size is a good way to get an accurately finished diameter hole.


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## woodchucker

Bob Korves said:


> Finishing a hole with a boring bar is the best idea for making a hole that ends up placed where you want it, and is also a way to open up smaller drilled holes while gaining accuracy, not losing accuracy.  It does not save time, however.  I have never done boring on a drill press, don't really have a setup put together that would do that, but boring holes sure works great on the lathe and on the mill.  Taking the last few thousandths with a reamer of the correct size is a good way to get an accurately finished diameter hole.



I have had mixed results with reaming. And recently when I saw the gunsmiths use a floating reamer, I realized my tailstock is the reason reaming doesn't work all the time. I think it's the wear in my bed, depending on where the tailstock is setup and where the wear is.  I want to take a look at that, or make a floating holder. Seems like it would be like a nice project.


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## mikey

Mitch Alsup said:


> So, this thread advocates going directly to the size of hole you want without drilling smaller sizes out first.
> What is the backup plan if your lathe/drill press/mill does not have enough power to drill the hole in one step?



Mitch, you make a valid point. Like @Highsider said in post 41 of this thread, it can be tough to drill a big hole without first using a pilot drill and he is right. 

So, how big is big? I find that once a twist drill gets much above 5/8" I need either a pilot hole or a really rigid set up. The reason, of course, is that the tip of the drill in the web area is not cutting; the large surface area of the tip on a big drill is too large for us to literally push through the material without a lot of power and leverage so it spins and the cutting area of the flutes cannot engage. A pilot hole overcomes this scenario by eliminating this point contact, which is why we only need a pilot hole large enough to span the web of the main drill. Sort of makes sense, right?

I can't speak for others but I spot drill and go to the main drill for everything up to about 1/2" in most cases. On my lathe, I can go up to about 3/4" (using a morse taper shanked drill). Once I reach these limits, I use a pilot drill large enough to just span the web of the big drill I'm using and accept that my accuracy will be a tiny bit off. That's okay since big holes for me are usually either through holes for a bolt or are roughing holes in preparation for a boring tool. 

Even with a properly sized pilot drill there will be some bouncing of the main drill but I find that if I gently engage the drill and allow it to shave a small bevel before applying pressure I have a lot less chatter. Once the tips of the flutes are buried, I pour on the leverage to cut the hole. 

Hope this helps.


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## cg285

a good friend who is the milling foreman for a fairly large manufacturing co uses center drills, so he says and recommends. maybe some day if i no longer have a dozen projects facing me i may do a comparison.


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## Bob Korves

cg285 said:


> a good friend who is the milling foreman for a fairly large manufacturing co uses center drills, so he says and recommends. maybe some day if i no longer have a dozen projects facing me i may do a comparison.


Lots of people use center drills as pilot drills, especially those who own lathes.   They are rigid, probably the most rigid drilling tool, and they are already in the lathe tooling, nothing needed to purchase.  They are designed for placing center holes for work to be held between centers, not for spotting holes for drilling.  However, the cutting point of a (larger) center drill, not including the cylindrical portion beyond it and before the wider cutting section, just the tip, makes a nicely formed divot for a larger drill to follow.  The massive rigidity keeps the tool from wandering.  If you use it like how it would be used for placing a lathe center, then I think it loses some ability to help center the following drill, unless the following drill has a smaller angle than 60 degrees (unlikely.)


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## Bob Korves

petertha said:


> So theory says 118 spotter should be better than 120 but I'm having trouble seeing anything significantly different between them.


Actually, I think the spotting drill should have a slightly larger included angle than the following drill for most scenarios.  If we are using the first bit to locate the hole, then we want the second drill to follow the first drill as accurately as possible.  If the spotting drill is the same angle or narrower than the following drill things can get interesting at the moment of first contact of the following drill.  Any asymmetry or runout or location error will cause one flute of the drill to contact the work before the other.  That starts a dance called "walking."  The farther out from the center of the hole that contact is made, the more leverage that is snagging on the drill until it starts to cut.  Something called "lobing" can happen where the grabbing escalates, causing big vibration and making three or more lobed divots in the hole, considerably oversize.  I have had that happen often on not so rigid drill presses and hand held drills.  It also happens on a smaller scale, and still ruins holes on heavier setups.  If the angle of the cutting edges on the primary bit is larger than on the following bit, then the first thing to make contact is the chisel edge of the following drill.  If one hits before the other, the leverage on the drill is much diminished, causing much less leverage induced walking, and also rapidly making a seat to support the tip of the drill, the support increasing as the diameter of the drill in contact with the hole is also increasing.  No drama, the drill stays in the middle of the divot from the spotting drill.  More accurate as well.  That is how I see it, and using that technique has helped my drilling immensely.  I do not use it all the time.  If I am using my rigid mill and drilling into rigidly held work with a smooth surface 90 degrees to the drill, then why waste time with a starter drill?  Use a screw machine (stub) length cobalt drill with a 135 degree split point and just peck it a couple times and then get on with drilling, much time and effort saved.


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## David S

First let me say that I think Bob's post above is an excellent summary and guideline.

For years I always used centre drills for spotting and was often not too happy with the results but just figured "that's the way it goes some times".

When this thread started I did what lots would do and googled it.  My second suggestion is to forget doing a google search.  I found much conflicting information.

Instead I suggest that you get a couple of spotting drills and do experiments.  This is what I did and was very impressed with the improvement.  I use 120° spotters for 118° drills and a large 135° stub drill for spotting all my smaller 135° stub drills.

I normally use small bits under .250" and under magnification it was easy to see the following bit wobbling around when spotting with a centre drill and how steady the bit was when using a 120°spotter.

David


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## petertha

Bob Korves said:


> Actually, I think the spotting drill should have a slightly larger included angle than the following drill for most scenarios..



You are exactly right. I had a brain fart. A 118-deg spot cone would see the entire cutting edge of a 118-deg drill in simultaneously contact when they meet. Maybe the only reason it is even appearing to work without problems is one or both are not ground to 1-deg precision. 
Now I will write on the afterschool blackboard: 120 for 118... 120 for 118.... LOL


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## eeler1

I drilled a hole today


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