Twist drill bits need to be sharp in order to cut a clean hole. However, drill bits tend to lose their sharpness after prolonged use. The more you use the drill bit, the faster it will go dull, especially if you often drill at an angle or you don’t regularly withdraw the drill from a hole to clear the debris that accumulates as you work. Sharpening drill bits is a fine art and needs to be done just right. If you don’t, you’ll encounter problems further down the line. The sharpening needs to be even for the twist drill bit to be effective. When you start sharpening your own drill bits, don’t be surprised if you make mistakes at first. It can be best to practice on some cheap drill bits first.
Step 1 - Angles
Before you begin drilling, it’s important to know exactly what angles you need for different parts of the twist drill bit. If you don’t achieve these angles, the bit will still cut but not in the way that it should. If you’re working within specific tolerances, this will be a significant problem.
The drill point angles need to be equal, at 59 degrees each, so that you achieve a total angle of 118 degrees. The cutting lips have to be the same length and the clearance behind the cutting lips of the bit has to be between 8 and 12 degrees.
Step 2 - Measuring Angles
You’ll need an adjustable protractor to measure the drill point angles as well as the length of the cutting lips. However, for the clearance behind the cutting lips, you’ll only need to rely on your eyes. Thankfully, as long as the angle is between 8 and 12 degrees, you’ll usually be fine.
You also need clearance on the cutting lips otherwise you’ll be wondering why your drill isn’t cutting properly. At the same time, you can’t allow too much clearance or you’ll end up weakening the cutting edge which could lead the drill bit to break.
Step 3 - Using the Grinding Wheel
There’s a definite technique to the freehand grinding of twist drill bits but before you start, it’s important to bear in mind that you can’t allow the bits to become too hot. Don’t hold the bit down on the wheel. Instead, pass it lightly over the well to the point where you’re able to comfortably touch the tip without it getting hot. This takes longer, but gives you a better edge. Allow the wheel to do the work for you.
Hold the bit on the forefinger of your hand and ease it against the grinding wheel. The cutting lip needs to be horizontal against the wheel and the twist drill bit should be at an angle of 59 degrees.
You are now ready to begin grinding which you’ll be able to do with three movements. Make sure you wear safety glasses during this process. As you rotate the twist drill bit, move it to the left and downward. You’ll need to do this a number of times as you pass the bit over the grinding wheel in order to be sure you’ve sharpened the bit properly. Continue, checking the tip with your fingertip until you achieve the sharpness you desire. Clean the drill bit to remove any particles of metal before using it.