For many years I have used a Drill Doctor to sharpen drill bits, always feeling a little guilty as I have prided myself in sharpening just about anything freehand. This is excusable for very small bits, but 1/8" and up should be doable by hand ... well, I have seen these demonstrated for some years. Anyway, recently I decided that it was time to learn, and especially with bits 3/8" and up since these were time-consuming on the Drill Doctor.
For woodworking, twist drill bits have a 30 degree slope to each side. One cannot, however, simply grind the side slopes square and expect them to work. The cutting edge requires a relief angle otherwise it will not cut. In other words, sharpening a drill bit is not like sharpening a chisel or plane blade - the drill bit cutting edge needs to be both square (at the face) and rounded (from the face back).
To train my hand, I came up with a guide (or jig). This presents the bit to a bench grinder wheel at 30 degrees, and then holds this constant as the bit is lifted against the wheel to create the relief. Here is the guide ...
The fence lies at 60 degrees to the front, and there is a 19mm (3/4") dowel to rest the bit on.
The jig is clamped to the platform on my bench grinder (which uses an 80 grit CBN wheel here).
The drill bit is pushed along the fence and against the wheel, with the cutting edge on the horizontal ...
Once the cutting face is ground, rotate the drill bit upwards so the the back is ground at an angle (actually, it should be rounded). That is the relief edge ...
The result is like so ...
Proof of the pudding ...
Regards from Perth
Derek
Sharpening twist drill bits freehand
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Re: Sharpening twist drill bits freehand
#2Once again, Derek, you have given us the perfect solution to an agonizing problem that all of us face! Thank you. Philip
Re: Sharpening twist drill bits freehand
Edited #3One correction to make: the photos of grinding are reversed. (I took these photos a few weeks back, and lost the memory of what was happening at the sharp end).
Also, as noted, this is a jig to train the hand. You will discard it after the angle and rotation become familiar.
Regards from Perth
Derek
I reversed the photos. Lemme know if I did it wrong. --Peter
Re: Sharpening twist drill bits freehand
#4I learned to sharpen drill bits in high school shop class about sixty years ago. The teacher gave us a bunch of old worn out bits and we practiced and practiced. About fifty years later I found I had a really chipped and dull bit about a 1/2" in diameter and needed it sharp. I wondered if I could sharpen it and gave it a shot. (Why not, you can't ruin something that is already ruined) Went to the grinder and did it in a couple of minutes and it may not be perfect but it works just fine. Touch them up regularly now. Muscle memory is better than the regular kind. I scribed a little scratch on the tool rest and the correct angle.
Re: Sharpening twist drill bits freehand
#5
Or not by freehand 
https://youtu.be/m3Al3bfb9-0?si=OOpAsF3FJkiCJqsP
Re: Sharpening twist drill bits freehand
#6
Simple and sweet, Derek. Holding the edge horizontal is a key instruction. It's hard to tell from the angle of your photos, but the initial square grind (before rolling the bit upward) should ideally be made on the centerline of the wheel to avoid a negative rake angle.
Cheers,
Ellis