Some success at drill sharpening

[evfreek]

Hi.  I took a break from the usual projects and tried hand sharpening some drill bits.  I still remember the metal shop class in which this subject was taught.  The instructor gave us a 3/8" drill bit and asked us to follow the contour and grind it.  It was easier to do this than sharpen a bad bit.  Then, he showed us how to tell if it was good or not (equal edges, cuts, correct sized hole, etc).  Then, he goofed up the ends and asked us to fix it.  Finally, after the lesson, he told us all that we were lousy, and we should all go to an estate sale and buy some junk drills and fix them ourselves.  Only then would we learn.

 

Well, years later I did this.  Seems that youth and its rebelliousness keeps us from getting the true message and improving ourselves.  The instructor meant exactly what he said.  The youthful and incorrect interpretation is, "hey, he told me I suck and now he wants me to do something dumb."  That's not what he said.

 

So, there was a bottle of old drills at an estate sale, and I asked the professional seller what he wanted for them.  He said $10.  I told him that this was kind of steep, but he said that he normally sells drill bits 3 for a dollar.  I replied that many of the bits were broken.  He said that there were enough good bits to be worth the money.  I gave him the ten.

 

A lot of the instructions on the Internet are confusing.  Most of them are correct.  Anyway, the important points are get the point angle correct (most important), cut enough relief (second most), and keep the cutting edges equal (third most important).  One of the most important tips is to use a drill gauge. These are cheap, and they are easy to make if you are broke, especially after buying tools at an estate sale.

 

To test the drills, I drilled mild steel without lube.  I used a hand crank drill.  Using a cordless drill or even worse a drill press misleads you since you end up forcing a dull bit.  Just a tiny punch mark.  Any wandering, and the drill is not good.  Look for equal curls of swarf, and easy quick cutting.  Sharpening 3/8 is easy.  3/16 to 1/4 is harder, and you may have to go back to the drill gauge and ask yourself some questions.  Less than 1/8 is almost impossible, but I figured out a trick.  The main problem is that you cannot see.  The most important factor with tiny drills is the starting position.  If you goof this up, you will mangle one cutting edge.  Here is the trick.  Just concentrate on getting the point angle.  Then, grind a 4 facet relief with a hand stone.  Believe me, it will take less time than going back and forth to the grinder.  Another thing I want to try is a loupe.  People say throw away any dull bits less than 1/8.  There may be some sense to that recommendation.

 

[swedefiddle]

Good Morning,

 

Take a piece of cardboard or sheet metal and cut a drill angle gauge (normally 59 degrees = 118 degrees). You can make some marks so you can figure if you are centered or not (if you are not centered the drill will cut a larger hole).

 

Be Patient, GrassHopper. :) :)

 

Neil

[Rich Hale]

Two hex nuts place together flat to flat will have a angle between them that works for drill angles...

[jmccustomknives]

I was taught in school shop class to use a bench grinder, I found by accedent that the disc sander worked much better.  For big bits that are rough you'll still need to shape them on the bench and finish them off on the disc.  As always, keep 'em cool and wear your PPE!

[Frank Turley]

In using a bench grinder on a cutting lip, it helps me to direct the drill toward the center of the grinding wheel. The drill will be horizontal before twisting to gain relief. Just my experience. 'General' makes nice, reasonably priced, stainless gages.