Sharpening twist drill bits freehand

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Derek Cohen (Perth Oz)

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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 ...


2.jpg




The fence lies at 60 degrees to the front, and there is a 19mm (3/4") dowel to rest the bit on.


1.jpg




The jig is clamped to the platform on my bench grinder (which uses an 80 grit CBN wheel here).


3.jpg




The drill bit is pushed along the fence and against the wheel, with the cutting edge on the horizontal ...


4.jpg




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 ...


5.jpg




The result is like so ...


6.jpg




Proof of the pudding ...


7.jpg




Regards from Perth


Derek
 
You should be able to do these freehand, no jigs etc as I was shown years ago. Put the edge on and back it of, not so easy on small drills without light and magnification.
 
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As an apprentice engineer, I was give 100 drills a month to sharpen for 4 months by one of my section forman. It was good training for freehand grinding, plus we also had to dress the stones as part of the training.
I thought it was a bit over the top for 4 months, but found out some others did it for 6 and 7 months. Turned out that forman had each one checked and used by the qualified engineers.
And when you where producing consistently sharp drills, then he stopped giving you the task.
Apparently 4 months was reasonably short time, so I was quite chuffed with myself.
That's was 44 years ago, still get a reasonably decent grind now.
 
One 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
 
Very neat idea, that could save me a lot of frustration and possibly teach me at the same time - thanks.
 
As an apprentice engineer, I was give 100 drills a month to sharpen for 4 months by one of my section forman. It was good training for freehand grinding, plus we also had to dress the stones as part of the training.
I thought it was a bit over the top for 4 months, but found out some others did it for 6 and 7 months. Turned out that forman had each one checked and used by the qualified engineers.
And when you where producing consistently sharp drills, then he stopped giving you the task.
Apparently 4 months was reasonably short time, so I was quite chuffed with myself.
That's was 44 years ago, still get a reasonably decent grind now.
Did the same as an apprentice elec fitter- we had to do it (by eye) until we were good at it...
Still sharpen by hand even today lol
(sharpen the edge at the correct angle for the material, then 'roll and twist down' to put the 'back curve' on it- after a while it becomes second nature lol)
Its hard to explain that 'roll and down' motion
 
Have a look at 4 facet grinding…most manufacturers are now using this grind..
 
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A simple guide to whether or not your drill cut is to gently rotate into your palm you will feel the cutting edge if you've got relief. Also I experimented to try a make a drill drill a slightly bigger hole by offset grinding the centre point. It takes a decent offset and a chunky drill to work. Try it. When you get the knack you can remove much of the Web to make it easier to sharpen on middle/big drills. Ie the bit behind the cutting edge. Other point angles are available to.
 
I had an Eclipse drill sharpening jig when I was still at school. It was terrible! When I eventually learned to sharpen them properly (from a book) it was such a revelation! Still do it. Not particularly well, but good enough for me.
 

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