# Drilling errors and solutions



## Kaylee Frye (Dec 13, 2017)

Hi all, 

hope I'm in the right forum - this is barely machining, but I need a machinist's mindset for advice. 
I am the metalworker for a small custom furniture shop, and lately we are making a lot more designs that rely on bolt connections rather than welding.

I am able to finish the projects, but I can't get the drilling accurate enough to make the parts interchangeable- my most recent example is that I had to make a set of three conference tables. Since the parts couldn't be interchangeable (misalignment by 1/32 here and there), I had to mark every individual piece and mark its orientation, which I felt was sort of a waste of time, a brain cramp to not mix up, and will make installation a little less straightforward for the install team. 

Basically, I'm asking all for help, ideas, and brainstorming on how to standardize my drilling process to be a little less custom and individual, so that I have to mark every side of everything every time. But who knows, maybe this is just how things are and I just have to get used to it? 

I'm attaching a photo of a perfect example of my drill bit not catching my center punch mark, and drilling misaligned holes. Why?! It's gotta be something obvious that I'm missing? maybe I have to sharpen up those centerpunches? Do I really have to make a jig for almost everything? I know to centerpunch for the drill bit to catch, but I still have a hard time making that drill bit catch instead of slide around the punched dimple. Maybe I'm not punching a big enough dimple? I've read that people will start their holes at 1/4" but it seems maybe I have to start even smaller to end at an accurate enough 1/4" hole. 

I'm also attaching 2 photos of the conference table legs I was working on --- I used a steel jig I welded together to mark the holes on the legs, and then I used the line up of the legs as a jig to mark the holes on the long support runners. Maybe projects like this have to end up being very individual, steel warps and bows and is never perfect to begin with. Or maybe I should have enlarged all holes on the runners by 1/16" or so"? During the build, I resisted enlarging all holes, only enlarging when I had to, because the tighter the hole, the better the table pieces fall into square. What do you think? I feel like there must be an easier way that I haven't thought of. 

Thanks so much to all who share any thoughts! It's really appreciated, I promise to come back to the forum and leave my own advice where I can in return.


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## David S (Dec 13, 2017)

I think your punch marks have to be larger to catch the point of the bit.  Also since your holes are shallow you may want to use a stub bit, which may give you more control and will be stiffer.  And perhaps a handheld jig that fits over the bar may also help.  It is too bad that there isn't some place you can allow for adjustment, like a slot or over size hole.

David


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## RJSakowski (Dec 13, 2017)

In making interchangeable parts here are two solutions: One is to make a jig which contains drill guides for locating the holes.  That would be fixed to the part in a reproducible fashion and the holes drilled through the guide holes.  Drill guide bushings are available that are hardened to prevent wear.  This technique will save you much time in locating and center punching and should bring your positioning accuracy down to a few thousandths of an inch. 

The second method is to simply drill oversized holes in on or both of the mating pieces.  The holes would be oversized sufficiently to accommodate your positioning errors.

Here is an example of the drill guides.  They are pressed into larger holes in the jig.
https://www.travers.com/h-style-precision-drill-jig-bushings/p/99067/?keyword=drill guide bushing&lite=true&pricelistname=SITE&hawkmm=2


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## Bob Korves (Dec 13, 2017)

For drilled holes that will be repeated, use a jig, at least over the width, as often as possible.  In fact, use jigs for anything that you will be doing again.  If it is used enough, a jig saves the time spent making it many times over, and makes the work more accurate and more repeatable, as well as making the parts interchangeable.  For one-off hole locating in structural steel, I tend to use two center punches, a 60 degree sharp prick punch to accurately mark the hole center, followed by a much wider angled sharp punch, in the 120 degree included angle range for 118 degree drills, which leaves a divot the drill can truly follow, starting in the center of the divot.  The divot only needs to be slightly bigger than the chisel point of the drill.  Another concept I use when using a drill press (or mill) with flat and smooth work 90 degrees to the drill is to simply use a 135 degree split point stub length drill which starts it's own hole without walking.  In that case a setup more rigid than loose on a drill press table is needed to locate the hole.  A mill and solidly clamped work is necessary, or a drill press with solid stop and fence, and the work clamped down.  Like you, I find it really annoying when a hole ends up in the wrong place and it has to be made oversize to fit.  If I was a pro like you I would spend lots of thought on shop made tooling that will speed your work while also making it more precise, even in a custom shop.


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## RJSakowski (Dec 13, 2017)

When  only two holes are involved, one of the holes is often sloted in the direction of a line between the two holes.  This allows for assembly when there is error in positioning the holes.  It will not correct any rotational error caused by an error in locating the holes in the direction perpendicular to the line between the holes, however.  It is also not easy to do if your are working with hand power tools.


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## Robert LaLonde (Dec 13, 2017)

A drill jig is definitely helpful if you are doing this manually.  Stub bits are a big help on machines where flex is an issue, but I'm not sure it will help a lot here.  Even using a drill jig a punch mark can help the drill bit find its correct location.

However given that you are doing this manually I doubt you have the ability to make a drill jig, so consider this.  Punch accurately, punch harder, pilot drill, then drill.  A smaller drill bit will find and stay in the punch mark easier.  The pilot hole will keep your bigger drill in the correct location.

A sort of 2 in one approach might be to use a pilot point drill bit.  The problem is once the pilot point is dull they are done and they are hard to resharpen.  Maybe just having a bunch of them on hand would do the trick.  Its always a trade for cost of time vs cost of tools and materials.  I would avoid step drills (Christmas Trees) as it has the same problem as a pilot point and costs more.  Also an over zealous helper can do alot of damage with a step drill.

I didn't mention split point bits above.  They do not tend to wander like chisel point bits, but they are not what you typically find in metall cutting drills from the usually sources.  You still need a big enough punch mark to locate the drill and its still easier to drill a smaller pilot hole first.


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## jcp (Dec 13, 2017)

If you are marking the layout accurately and the problem is picking up the scribed intersection, try using an automatic center punch. They have  steep angle tip so you can see the scribe intersection clearly. After the automatic c/p mark, use a 118/120 center punch (as mentioned above).


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## Kaylee Frye (Dec 13, 2017)

Wow, thanks everyone! This is all super helpful to think about. Of course everything points to I really need a mill eventually to make pretty slotted holes, but! Encouragement on the value of taking time to make the jigs and the points about the different types of bits and center punches is helping me think. Can't mill jigs yet, but I've been welding some up alright. Good to know I'm not wasting time by doing so, and good to know I have more options when it comes to the drill bits too.


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## Bob Korves (Dec 13, 2017)

About 35 years ago I made 10 of these cookie cooling racks for all the women in my life (that would be mom, sisters, aunts, grandma, friends, etc., and just one GF...) as Christmas gifts.  The jig I used for spacing and drilling all the dowel holes is also in the pictures.  The jig was made and set up in less than half an hour, rough cut wood, nailed together, and one old bolt as an indexing pin located at the correct distance from the fence.  The jig was fixed to the drill press table with C-clamps.  I chose a drill bit that drilled holes to a tight tapping fit for the dowels I had bought.  The hole spacing and centering was carefully set by testing on scrap wood until correct.  The pin (bolt) indexes against the end of the rail for the first hole, and after drilling it is advanced and indexed over the pin, repeat until 10 holes.  A sacrificial block was pressed down on the top of the rail while drilling to prevent tear out.  Repeat for 200 holes on 20 side rails.  Cut the 50 36" dowels in half for 100 18" parts (using another jig/stop to get all the lengths correct easily, finish sand all the parts, use a mallet to pound the rails and dowels all together tightly (no glue), sand the slightly protruding dowels flush with the rails on the belt sander, soak with food grade linseed oil using a saturated rag, finished!  Took most of one day to do them all from start to finish.  Jigs do not at all have to be fancy and expensive.  Anything that makes repetitive work go more smoothly, quickly, and accurately is worth the effort.  There were only a few measurements on this entire job.  I could be set up to do another run in half an hour or less.  I cannot even guess how long it would have taken to do the 10 racks by laying out and drilling all 200 holes individually, and measuring and cutting 100 dowels and rails individually, with no jigs at all -- and the finished racks would have been much less uniform.


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## mikey (Dec 13, 2017)

If you are using a hand-held drill, it isn't unusual to have drift when using jobber drills. If it was me and I had to make multiple pieces all fit, I would make a jig to fit a sharp prick punch so marking out is consistent. Then I would use a rotabroach to drill the holes. A rotabroach has a sharpened pin to orient the cutter and it will locate in the prick punch hole accurately. You can also visually see when a rotabroach is cutting evenly so you are less likely to cant the drill. A rotabroach also cuts burr-free holes so you have less clean up to do.


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## benmychree (Dec 13, 2017)

mikey said:


> If you are using a hand-held drill, it isn't unusual to have drift when using jobber drills. If it was me and I had to make multiple pieces all fit, I would make a jig to fit a sharp prick punch so marking out is consistent. Then I would use a rotabroach to drill the holes. A rotabroach has a sharpened pin to orient the cutter and it will locate in the prick punch hole accurately. You can also visually see when a rotabroach is cutting evenly so you are less likely to cant the drill. A rotabroach also cuts burr-free holes so you have less clean up to do.


Add that Rotobroach cutters are expensive and difficult to sharpen, takes three different setups on a tool & cutter grinder to do it.


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## mikey (Dec 13, 2017)

benmychree said:


> Add that Rotobroach cutters are expensive and difficult to sharpen, takes three different setups on a tool & cutter grinder to do it.



True, but they last far longer than a drill before they dull, provided you use a wax stick lubricant each time.

Edit: I emailed Blair to see what they charge to resharpen one of the broaches. We'll see what they say.


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## brino (Dec 13, 2017)

If you are doing repetitive operations, then the advice above of making a jig is great.

If you have problems with aligning the centre punch to a mark, then an optical centre punch makes that easier, but can be a little slower:
http://www.leevalley.com/en/wood/page.aspx?p=45502&cat=1,180,42311

-brino


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## MarkM (Dec 13, 2017)

I would look into drill bits with a 4 facet grind.  They don t walk around like regular drills and also way less blow through on your exit hole.  I grind drills for a Wood Cabinet Company with the four facet and they have been very impressed with it s accuracy of hole size and life of there drills in production.  First thing I do when i buy a drill is put the four facet grind on it.


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## ch2co (Dec 13, 2017)

* an optical centerpunch came with my used lathe, I thought is was stupid. Now it’s one of my favorite hole marking tools.  
Grumpy One*


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## Robert LaLonde (Dec 14, 2017)

MarkM said:


> I would look into drill bits with a 4 facet grind.  They don t walk around like regular drills and also way less blow through on your exit hole.  I grind drills for a Wood Cabinet Company with the four facet and they have been very impressed with it s accuracy of hole size and life of there drills in production.  First thing I do when i buy a drill is put the four facet grind on it.



4 facet grind?  Do you mean make it into a split point?  LOL.  Yes split point drills are less apt to walk and wander.  Still have to do a good job of making the edges equal length too.


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## MarkM (Dec 14, 2017)

No a four facet grind is not a split point. Four facet are the most accurate of all drill grinds.  Perfect drill geometry on both sides when done proper.  Equal lip length and a true centre that doesn t need a pilot hole or centre punch.  Split points are still a chisel with a thin web that don t centre them selves when they *drill.  They also,produce a very accurate hole. Almost reamed. * I don t know why it is highlighted. My ipad is on it s way.  Disregard that. Not shouting_. I have seen one grind of a four facet produce over five thousand holes on a screw machine on more than one occasion.  Yes a six spindle Davenport and brown and sharpes 2 b.  Try one it might impress you. For the o.p. They don t walk it may solve your problem._


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## umahunter (Dec 15, 2017)

First thing I would do is use a carbide  scribe you can get one at any welding shop scribe a cross this will leave a slight spot in the center a prick punch will sit in then use a bigger punch to provide  a deeper  dimple start the hole with a centering  bit https://m.harborfreight.com/center-drill-countersink-set-5-pc-60381.html   then drill with a small drill bit then your final size it helps if your first bit is big enough to search the Web of your final bit if you wanna try a rotobroach bit you can get a Chinese one with a centering pin on ebay for under 20 bucks for a half inch bit but you will have to have an adapter or a drill chuck big enough to chuck a 3/4 inch bit


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## umahunter (Dec 15, 2017)

Carbide  scribe https://www.google.com/aclk?sa=L&ai...ahUKEwjKv8SHvovYAhVJzGMKHdlEA0gQwg8IJg&adurl=


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## umahunter (Dec 15, 2017)

1/2 inch  annular  cutter  with center pin https://m.ebay.com/itm/1-2-X-1-HSS-...hash=item27d0dd54b0:m:mvvJ83A9C-pohK-E1XxWKVw they have many other sizes I bought a 1/2 inch from them  to try and it works great


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## Larry42 (Dec 15, 2017)

Kaylee Frye said:


> Hi all,
> 
> hope I'm in the right forum - this is barely machining, but I need a machinist's mindset for advice.
> I am the metalworker for a small custom furniture shop, and lately we are making a lot more designs that rely on bolt connections rather than welding.
> ...


Consider using spotting drills to start your holes, another solution is centering drills. A huge variety is available @ MSC. Both are short and don't tend to walk. I often use screw machine cobalt drills because they are very stiff and don't flex. Like someone said 135 degree points also don't walk as bad.


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## Uglydog (Dec 15, 2017)

Kaylee Frye said:


> hope I'm in the right forum - this is barely machining, but I need a machinist's mindset for advice./QUOTE]
> 
> Kaylee Frye,
> Welcome to HM.
> ...


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## C-Bag (Dec 15, 2017)

There was a great vid by Jon on his NYCNC YouTube about accurately laying out. Even though for the last 10yrs of my wage slave tour was metal fabrication, this laying out then drilling holes was my nemesis. 

What Jon showed was how using a trisquare and the scribe to lay out your line accurately, then using an auto punch by feeling the scores made with the scribe. I could now get the absolute center of my scribe lines, then like has been mentioned come back with a good sharp center punch. The other thing was using a two step 1/4" drill to start the hole. But all of this is moot if you are not at least using a drill press because it's impossible to stay totally straight by hand. YMMV.


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## spumco (Dec 24, 2017)

I can't drill for diddly by hand.  I find that I simply can't figure out how to drill perpendicular to the workpiece no matter how hard I try.

I solved this by getting a mill.

Not ideal for your situation, I suspect.  As an alternative, a small mag drill will help quite a bit.  You can mount it on a plate with some additional clamps for the sections you're drilling and have, essentially, a portable drill press that will drill straight holes.

Stub length, good quality split point drills, plus a spot drill will help with the point wandering if the center punch is shallow.  Actually, with a spot drill, stub length drill, and a mag base you don't need to center punch at all.


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## Kaylee Frye (Jan 16, 2018)

Thank you all for all this input, it's really opened up the world of drill accuracy for me! I went into this project now confident I was not wasting my work time building jigs. I was able to weld up some decent enough jigs, and if anything was inaccurate- at least it was all equally and very consistently inaccurate! I also strategically enlarged holes by just 1/64 and 9/32 here and there to make the project more easily put together in the end. I'll be working on another set of the same tables I pictured above soon, so I'll also try out on the pair of holes to keep one tight and the other enlarged and see if that also standardizes and eases the assembly even more. I bought a handful of different types of the drill bits you guys mentioned to experiment with as well, and already I do notice the difference in wandering. I'm attaching some pics of the jigs I made and the resulting project which is a big ol' rectangle to provide as a wall divider frame in an office. Thanks everyone, I would have been so stressed on this one without your support.


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## David S (Jan 16, 2018)

Kaylee, thanks for the update and seems like you are getting better repeatability.  

David


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## C-Bag (Jan 16, 2018)

Good job. Now that you have a toe hold in jigs I guarantee you will never go back. The more you make jigs the more you can design them to be reusable for other projects. And the quicker you can make them and see how much time they save. We also had a huge jig table that had 2  2x8" channel iron that could be moved on the table bed w/legs. I used to make a LOT of conveyer's for fruit packing and if they weren't square, the belts wouldn't track. We used that jig table for everything......wish I had that old table still sometimes.

The next level is like an RF-30 mill/drill(because they are cheap) with a cheap Igaging DRO. I'm still wondering why I waited so long to do this upgrade because my level of accuracy has now gone to scary perfect. And after these years of wishing for better but just thinking it was my lack of skill.

Good luck, onward and upward.


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## tq60 (Jan 20, 2018)

Larger holes are sloppy...

Our building "kit" uses 5/8 bolts and the manufacturer pre punches holes at 11/16 so easier to assemble but pain to align... barn style too many parts to align....

But it does help.

Dewalt sells a drill index with 2 step or piloted bits that work well.

For any "production" environment such as yours where portable drilling is the process jigs or fixtures are a must.

Also male and female help so you can drill the part and place to exact match.

To further define the outcome add guides such that the fixture is held in alignment to part.

Take additional time to make it so the wife can do it and results will be worth the effort.

Having holes NOT in a straightline may be stronger bond so take time to make the jig and the hole count determines if bushings needed.

Another thought is if you have many different parts but could use a standard bolt pattern then make a drill guide with bolt battery then fixtures to apply it to different parts.


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## ezduzit (Jan 20, 2018)

What you are doing wrong is not using a spotting drill.


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## Firestopper (Jan 20, 2018)

If you where to add drill bushings to you jig, you will have consistent results for a long time. I been using the same drill bushing on my jigs since 2003 with thousands of holes drilled. Drill bushings also help when hand drilling.


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## magicniner (Jan 21, 2018)

spumco said:


> I can't drill for diddly by hand.  I find that I simply can't figure out how to drill perpendicular to the workpiece no matter how hard I try.



Get a small piece of mirror or mirror finish stainless with a hole in the middle, with the mirror on the surface you're drilling and your drill through the hole, the drill is perpendicular when the drill bit and it's reflection appear to be one straight bit - simples! ;-)


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## spumco (Jan 21, 2018)

magicniner said:


> Get a small piece of mirror or mirror finish stainless with a hole in the middle, with the mirror on the surface you're drilling and your drill through the hole, the drill is perpendicular when the drill bit and it's reflection appear to be one straight bit - simples! ;-)



Great idea, but if I'm drilling by hand, I'm probably just making a butcher hole somewhere in the target vicinity.  Think spade bit in wood.  And I'm usually drilling at some odd angle and would need a 3rd hand to hold a guide.

If I need it precise, I use the mill.


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## TakeDeadAim (Jan 21, 2018)

C-Bag said:


> There was a great vid by Jon on his NYCNC YouTube about accurately laying out. Even though for the last 10yrs of my wage slave tour was metal fabrication, this laying out then drilling holes was my nemesis.
> 
> What Jon showed was how using a trisquare and the scribe to lay out your line accurately, then using an auto punch by feeling the scores made with the scribe. I could now get the absolute center of my scribe lines, then like has been mentioned come back with a good sharp center punch. The other thing was using a two step 1/4" drill to start the hole. But all of this is moot if you are not at least using a drill press because it's impossible to stay totally straight by hand. YMMV.



Ive seen Jons video and that technique works great to make one or two accurate parts.  However; this poster is looking for a solution to production drilling.  As suggested by many a fixture with drill bushings is the answer.  No need for layout or measuring each piece once the fixtures are made you simply insert the part and drill.  They last a long time, can often be used for multiple designs and have better repeatability


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