Before grinding a drill bit you must have very clear vision of what you are doing. This means the grinder must be brightly illuminated and, if you wear glasses for close-up work, you should have them on. The grinding wheel should be of fine grit and its face should be flat and square.
The first step in sharpening a drill bit is to grind the point angle.
Stand slightly to the left of the grinding wheel, feet apart. Hold the drill about a quarter of the way along from the point, using the thumb and forefinger. Rest these fingers on the grinder’s tool rest. Use the other hand to hold the drill at its shank.
Hold the drill so that it is horizontal but approaches the grinding wheel at an angle of about 60 degrees. Rotate the drill so that its cutting edge is parallel and close to the wheel. The drill can then be moved forward and the point ground.
The next step is to grind the lip clearance.
Use the left hand to swing the shank of the drill downwards and to the left. These movements are only slight. Remember to keep the right hand supported by the tool rest. As you move your left hand, use your right hand fingers to roll the drill clockwise about a quarter-turn and simultaneously feed the drill forward against the grinding wheel.
Practice doing these motions with the drill you just brought in from your workbench. Use the edge of the desk as the 'pretend' grind stone.
The sequence of motions is: left hand down and leftwards, right hand fingers rotate drill clockwise, both hands move drill forwards. Watch the cutting edge (red arrow) and you’ll see that as you do this, it moves forward and away from the grinding wheel. However, if you rotate the drill too far, or the left hand is not moved towards the left, the opposite side cutting lip (near to the point) will come into contact with the grinding stone – not what is wanted!
When the point angle and lip clearance have been ground for one face, do the other. Make sure that the point angle is symmetrical and centred.
When grinding use only light pressure and frequently pause to let the airstream cool the drill bit.
When learning to sharpen drill bits, don’t sharpen a whole bunch of drills! Instead, sharpen one drill and then try it out on a piece of scrap steel, seeing how well it actually drills holes. To be honest, many of my first attempts at sharpening drill bits resulted in drills that were worse than before they were ‘sharpened’. So you must evaluate the results of your grinding before proceeding further.
A properly sharpened drill bit should have equal cutting angles, equal length cutting edges and equal angle lip clearances.
Drill a hole through a scrap piece of steel. The drill should not chatter, squeal or stick, and shouldn’t need excessive pressure. The swarf (chips) should be continuous and produced in two lines, and the drill bit should be a tight fit in the drilled hole (ie remove the drill from the machine and try it back in the hole).
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