drill bits getting dull

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
 
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
Click to expand...
 
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.
 
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]
 
Last edited by a moderator:
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" ???
 
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
 
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
 
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
 
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.
 
You must log in or register to reply here.
Back
Top