Sharpening a drill bit on a bench grinder

 

 There seems to be many of us that are confused on the correct way to sharpen drill bits on a bench grinder. So here is the way it's done.

Many newer bench grinders have a convenient slot in the tool rest. That is there for this exact purpose. It is just a slot that is set at 30 degrees and is centred in the middle of the stone. If your grinder has not got this, then get out a protractor and make one. You could us a hack saw and round file or even an angle grinder.

  It is important that the face of the grinding stone is flat and square to the tool rest. We have all been guilty of just using the centre of a stone over and over. The end result is uneven ruts. That will be useless in drill sharpening. Many bench grinders come with a wheel dresser. They are quick and simple to use. Buy one if you don't have one already. A finer stone will do a better job, but you need to grind slower as it will be removing less material.

  Now down to the mystic art. If you look at a drill, you will notice there are 2 cutting edges. They will need to be even in length and angle. (pic 2)

 

The cutting edge is the highest point. The trailing shoulder should be lower, or the cutting edge cannot bight into the material.
When you position the drill bit on the tool rest, the cutting edge needs to be parallel with the tool rest. The slot in the tool rest is setting the drill at the correct angle. It is there just to position the drill bit. The sharpening  is achieved by pushing the drill into the stone, then lifting vertically up from the tool rest. As you push up, apply a bit more pressure as you go, That will ensure the trailing shoulder is ground down further than the cutting edge. It is fairly quick and when it's done right, you will see both cutting edges are even with a small straight line in the centre of the drill bit. The hardest part of the technique is how much to grind off as you lift the drill bit up the stone. Naturally, the larger the bit, the easier it is. A well sharpened bit should cut without much downward pressure with a curling swaf. HERE is a video demonstrating the process.