# drill bits getting dull



## SE18 (Dec 16, 2012)

Hi 
Building a follower rest for my SB9A and drilling thru 1.25" mild steel. Using HSS drill bits. After just one pass, they become dull (using plenty of cutting fluid and withdrawing bit a lot to remove swarf). Tried to grind the bits after watching tubal and someone else's videos but really hard to get the knack as the tips curve around in weird ways and the angles are crazy.

Cheers

Dave


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## Ray C (Dec 16, 2012)

If the bit itself has ever gotten too hot, it may have lost it's tempering and it's shot now.  Depending on the metal it's made of, temperatures above 400F (approximately) can change the original tempering. 

As far as the angles, try comparing your grind to a known, good bit.  




SE18 said:


> Hi
> Building a follower rest for my SB9A and drilling thru 1.25" mild steel. Using HSS drill bits. After just one pass, they become dull (using plenty of cutting fluid and withdrawing bit a lot to remove swarf). Tried to grind the bits after watching tubal and someone else's videos but really hard to get the knack as the tips curve around in weird ways and the angles are crazy.
> 
> Cheers
> ...


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## GK1918 (Dec 16, 2012)

You said it Dave the knack.  Kind of like after the training wheels are off thing your good ta go.
More hard to explain than do but I start with the cutting edge level to the grinder back and
forth lightly and sweep it downwards but keeping the same plane with the wheel and keep
looking at it.  Just dont be to aggressive a fine wheel and light cuts.  yes I had drill doctors
and I always had the habbit of cutting & saving power cords when they hit the dumster.
So this is a yes I can do thing.  Ever watch a sign painter- same thing.  Nice steady sweeps.


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## Ray C (Dec 16, 2012)

GK1918 said:


> ... stuff snipped...   yes I had drill doctors
> and I always had the habbit of cutting & saving power cords when they hit the dumster.



LOL:  Seriously now, there's got to be more good spare parts inside them than just the pigtail.


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## SE18 (Dec 16, 2012)

ok, thanks, I just returned again from the grinder; comparing good bits with mine; the angles are so crazy but the bit is improving bit by bit, I finally got a half decent web at the top and that helped some; but I have a lot more work ahead of me. I need to take a break for a bit.

I'm starting the hole with center drill and the hole diameter will be 5/16 for the follower rest to attach to carriage holes. I made one hole yesterday but that ruined 2 bits. I am in fact using a drill bit half of 5/16 size to get the hole thru then following with a 5/16.

BTW, how much pressure should you apply to the drill's capstan handle, a little, moderate, a lot?

btw, I did so much experimental grinding that the approx 4" long bit is now a 2" long bit

also, another question, the bit was pretty hot as I was taking heavy grindings, so I'm guessing I passed the 400 degree mark; that could be a problem I assume from what someone just said

my drill chart said to use the lowest speed (about 650 rpm) for over 1/2" steel so the pulleys are set for slow

Thanks

Dave


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## GK1918 (Dec 16, 2012)

Yes Ray i know it.  Its called "when flipping out.  Did you happen to see awhile back Mr Pete
flinging one of those drill jigs in the bucket    crash  thats only getting caught in the moment.

LOL    sam


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## Ray C (Dec 16, 2012)

It's very possible the bit is getting too hot as you're grinding it.  Once you get the knack down, it can be done in a few moments and never really get warm to speak of.  When drilling, use firm pressure but don't muscle it.  The curlies should be coming out evenly from both flutes if the bit is sharpened evenly.

Also, the temperature of 400F is approximate but recent reading about heat-treating indicates that moderate tempering (which decreases hardness) start to happen at/about that temperature for many of the common tool steels.  

As an aside, when I need to form a new lathe cutting bit and much  material must be removed, I dunk the bit in a cup of ice water and  really chill it down before making the first pass.  Once it gets warm to the touch, it gets chilled  down until very cold.  You shouldn't need to do this for drill bits  though but maybe it's helpful when you're first starting out.




SE18 said:


> ok, thanks, I just returned again from the grinder; comparing good bits with mine; the angles are so crazy but the bit is improving bit by bit, I finally got a half decent web at the top and that helped some; but I have a lot more work ahead of me. I need to take a break for a bit.
> 
> I'm starting the hole with center drill and the hole diameter will be 5/16 for the follower rest to attach to carriage holes. I made one hole yesterday but that ruined 2 bits. I am in fact using a drill bit half of 5/16 size to get the hole thru then following with a 5/16.
> 
> ...


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## Ray C (Dec 16, 2012)

...  I was absolutely shocked -and then I laughed like crazy!



GK1918 said:


> Yes Ray i know it.  Its called "when flipping out.  Did you happen to see awhile back Mr Pete
> flinging one of those drill jigs in the bucket    crash  thats only getting caught in the moment.
> 
> LOL    sam


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## irishwoodsman (Dec 16, 2012)

there is a grinding gage you can use i'm not for sure where you get them but its made for a drill bit, the army taught me how to grind them and i do it by eye anymore but i use a belt sander for mine and it seems to work better for me, and i pick up every broken or dull bit i can fine, you never can have enough. lol)mac


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## SE18 (Dec 16, 2012)

Hi Ray, thanks for the tip on lathe bits too, as when I was reading about drill bits, they came immediately to mind.

I rescued a copy of the 19th version of Machinery's Handbook several years ago that someone had placed in the trash before I even got a keen interest in lathe work. I'm spending a lot of time reading it. 

somewhere in the book, I'd have to find it the passage, it states that drill bits should not be dunked in water when sharpening. Something about the dunking that causes their molecular structure to be more suceptible to cracking; for some strange reason, lathe bits are OK to dunk in cold water; at least that is what I read


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## SE18 (Dec 16, 2012)

well, I got the book out, squinting at the small print on pg 1728 speeds and feeds section (a strange place for this tip as there's another section in the book that tells how to grind bits);

"Nothing will "check" a high-speed drill quicker than to turn a stream of cold water on it after it has been heated while in use. It is equally bad to plunge it in cold water after the point has been heated in grinding. The small checks or cracks resulting from the practice will eventually chip out and cause rapid wear or breakage."

and it continues with a lot of other tips; it mentions, btw, that it takes a lot of practice and experience to grind drill bits, so I take it I shouldn't feel too badly about my lack of skill at this point


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## Ray C (Dec 16, 2012)

Thermal shock can cause all kinds of problems.  I'm reading/learning a great deal about this.  Seriously though, if the metals are warm to the touch, cold water should not pose a problem.   As a matter of fact, all of the books I'm reading now use the "warm to the touch" rule for when it's safe to start the next step in a tempering or annealing process.  If it's too hot to hold (usually around 150F), dunking it in water is probably not the right thing to do.  Please try to find that section of book because I'm researching things for another project in the works and all information is appreciated.

Something to note.  If you've got a drill bit that's so hot that the cutting oil is cooking and smoking off heavily, you're in (or past) the point of no return.  Most oils boil at/around 450 and start to vaporize (heavy smoke) thereafter.  This is not to say the bit is completely ruined but, until it's properly annealed and re-tempered, it will not hold an edge the way it once did.

Also, in heat treating, the heat soak times for a piece are calculated by 1 cubic inch sections of the smallest part (or cross section) of the piece.  Soak times are typically 30 to 60 minutes per 1" of full cross section.  A large drill bit has what... maybe a cross-section of 1/8" or so?  That means it hits tempering range in 5 minutes.  A little drill bit will cook in a matter of moments.

Keep at it.  You'll get there.




SE18 said:


> Hi Ray, thanks for the tip on lathe bits too, as when I was reading about drill bits, they came immediately to mind.
> 
> I rescued a copy of the 19th version of Machinery's Handbook several years ago that someone had placed in the trash before I even got a keen interest in lathe work. I'm spending a lot of time reading it.
> 
> somewhere in the book, I'd have to find it the passage, it states that drill bits should not be dunked in water when sharpening. Something about the dunking that causes their molecular structure to be more succeptible to cracking


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## SE18 (Dec 16, 2012)

Thanks, Ray for encouragement. Warm to touch then it is! Thanks. And, the reference in the book is given just below your reply.

I now carry this handbook everywhere I go. It will probably take a few years just to read and re-read it. I consider it my must have.


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## Tom Griffin (Dec 16, 2012)

Dave,

Hand sharpening is a basic skill that all machinists need to master. Like all skills, it requires a little bit of basic information to get started and a lot of practice to become proficient. Hand sharpening a twist drill isn't all that tough as long as you break it down to the basics. Here's a video I just threw up on Youtube that may help out.

Tom

[video=youtube_share;y0SQkzScQk0]http://youtu.be/y0SQkzScQk0[/video]


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## JPigg55 (Dec 16, 2012)

Not knocking hand grinding here, but might consider getting a drill doctor. That's what I was planning on doing. Figure it would be faster ans easier than trying to hand grind.
Kind of decided this after listening to "Projects in Metal" podcast on iTunes. There's only an Intro and 3 other episodes. Not sure why they quit.
Any opinions here on the "Drill Dr" ???


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## SE18 (Dec 17, 2012)

thanks for the vid!

I have more questions now.

But first off, success! I actually feel confident now that I can do a fair job of sharpening drill bits by hand, but will need even more practice. I spend the entire day grinding bits and testing them out.

Now the problem. In the process of drilling all day, I think I work-hardened the hole I was working on thru mild steel 1.25" and now even a sharp drill that's new won't penetrate.  The other hole I made right next to it (for the 5/16 bolt I need to attach follower rest to carriage) went well and quickly with new bits, this is why I'm led to believe I work hardened the piece.

Now I need some suggestions.

I stayed awake last night thinking what to do. I'm thinking I need to anneal the piece but using a propane torch with that thick of steel might be problematic and I don't have mapp or oxy-acy.

Some of you admitted to using the oven when your wife is away and I may be able to sneak this piece into the oven as early as tonight as she'll be out shoe shopping.

Any ideas would be GREATLY appreciated!

Dave


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## Tom Griffin (Dec 17, 2012)

Dave,

It sounds like you made it over the hump and have realized that it is possible to sharpen your own bits. Now all it will take is more practice to develop the _feel_.

And now about that hole...Work hardening is only an issue in high carbon steels or certain stainless steels. Is it possible your "mild" steel is not what you think it is? Regardless, there are ways to get through it. Try grinding a bit with a flatter tip angle (135º +) and minimal clearance. Then, using a very slow rpm and lots of cutting oil, quickly force the bit into the work. The idea is to remove the hard spot before it removes the cutting edge on your drill. Another option is  to simply finish drilling the hole drill from the opposite side.

Tom


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## SE18 (Dec 17, 2012)

OK, I finished the video and it is even better than the man of steel, Tubal's, in my humble opinion. The closups really helped a lot.

So you don't need a fancy drill gauge; protractor will work!

A point, in Machinery's handbook, it advises not sharpening bits by hand unless you're an expert. It DOES NOT recommend a specific drill sharpening tool like the Dr. whatever it's called. There are good bit grinders but they cost upwards of thousands of dollars, so I'm told. Therefore, that's why it pays to handsharpen unless you got the money to spend on a good sharpener.

I think the hardest parts to sharpening is to find your place when you take the bit off the wheel. The second hard part is getting both sides even so the tip is dead center. My opinion on this is that unless you are very experienced, it is difficult to actually measure this and inevitably, your bit will drill a tiny bit larger hole than what the bit was designed to do.

OK, so I have a question about the video (please see my other questions just below this reply):

I noticed he ground 3 facets on each side, one of which was optional near the edge. Whether you grind 2 or 3 facets, should the facets blend (curve) seamlessly or, like he showed, should the facets be distinct angles like he shows. Or does it even matter.

I examined several drills and it looks like there are no facets. There's a continuous curve on each side.

Any insights????

Thanks

Dave


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## Ray C (Dec 17, 2012)

What is the depth of this hole?  If it's not too deep, just keep at it.  It's unlikely the hardening is very deep or wide-spread.  If it's a deep hole, maybe consider getting a carbide bit.

Also, if you're working with basic construction steel (A36) I've noticed it's sometimes inconsistent.  By that I mean that it seems to have internal hard spots.  I've noticed this many, many times especially when cutting with a chop saw.  You'll have one cut that goes like butter and the next cut off the same piece of stock material requires much more pressure and effort.  I can only attribute this to internal hard spots but would love to hear other theories.  I've had the same experience drilling holes.  This is why I stopped using A36 for machine projects and use 1018 or 1020 -basically the same stuff but better and more consistent quality.

Congrats on the new-found (and earned) skill.


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## SE18 (Dec 17, 2012)

thanks, Tom & Ray, I was typing when you replied


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## Tom Griffin (Dec 17, 2012)

Dave,

I opted to do the facet thing to keep it simple. Yes, you can create the clearance with one blended curve, but it's harder to do and I wanted to keep this video as basic as possible.

Glad you enjoyed it.

Tom


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## SE18 (Dec 17, 2012)

Thanks Tom, I reread you post and should have realized you were the one who made the video. Much thanks!

The facets are definitely easier. I just found a bit with facets, although most are curved continuously. Yes, It would definitely make things much more simple.

This thread has been a big help. Hopefully there are other beginners out there who might benefit from this.

Dave


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## Tom Griffin (Dec 17, 2012)

I just realized that the last part of the video dealing with the chisel point was cut off so I deleted the video and am reloading it. As soon as it's up, I'll edit the thread and update the link.

Tom


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## SE18 (Dec 17, 2012)

Thanks, Tom, it's definitely worthy of watching again! Your efforts are greatly appreciated. The closeups are really good, as is the lighting.


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## PurpLev (Dec 17, 2012)

Just to throw a few points to the mix:

I've used a drill dr. (back way), and found it's clamping mechanism lacking, also once the wheel starts to wear off (fairly quickly if you ask me) it starts to produce questionable results - looks great in the demos, and feels good the first week using it. but that doesn't last. then you go into replacing wheels and parts and its $$$.

On the other hand, sharpening by hand develops skills that stick with you long term. you never end up getting stuck cause you need a replacement part for your grinder that isn't available locally, and you are not limited by the size of bits you can sharpen.


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## SE18 (Dec 17, 2012)

Hi Sharon, thanks for your insights.

I had one other thought. If you went ahead a ground your bit, but were off, just a few thous or so (very very minor) in the balance of the 2 sides, you could actually create a bit that makes a slightly bigger hole. For instance if you had fractional bits but were lacking lettered or numbered bits, this might get you in the ballpark range for, say, following up with a tap for a hole you just don't have the bit for.

A second thought I had. You could maybe grind a bit and using a brand new bit, make a hole with each bit and see how close your ground bit came to the new bit. That way, you could sort of measure your bit grinding skills against a baseline.


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## SE18 (Dec 18, 2012)

OK, watched video again. Definitely a keeper! Thinning the web is something I didn't know about and will add to my sharpening habits.

BTW, what's the smallest size drill you sharpen? I imagine a magnifier helps when you get below around 1/4"


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## Tom Griffin (Dec 18, 2012)

SE18 said:


> OK, watched video again. Definitely a keeper! Thinning the web is something I didn't know about and will add to my sharpening habits.
> 
> BTW, what's the smallest size drill you sharpen? I imagine a magnifier helps when you get below around 1/4"




Thanks Dave, I'm glad it was useful to you. The last 2 minutes were cut off from the video on the first upload, but after four tries YouTube finally got it right.

Twenty years ago I could sharpen a 1/16" drill without magnification, now 1/2" is about my limit.  The old eyes just ain't what they used to be.

Keep practicing.

Tom


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## David (Dec 18, 2012)

Thanks for sharing drill bit sharpening via your video Tom. Very informative and helpful.

David


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## Tom Griffin (Dec 18, 2012)

David said:


> Thanks for sharing drill bit sharpening via your video Tom. Very informative and helpful.
> 
> David



No problem David. It's not viral material, but hopefully it will help a few people improve their hand grinding skills.

Tom


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## rwwells (Dec 31, 2012)

Thanks for posting video Tom,

Now out to the shop to practice on all my dull bits.

RWW


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## Tom Griffin (Dec 31, 2012)

You got a good deal, I'm only charging $100 for the video. 

Glad you guys enjoyed it.

Tom


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## Tom Griffin (Jan 5, 2013)

That is a well ground drill bit Shawn. Hand grinding is a basic skill that every machinist should acquire and you seem to have mastered it.

Thanks for posting the video.

Tom


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