One day I discovered I could hand sharpen twist drills, even though I always thought I would never be able to do it. Still, it is helpful to have a guide to check the angle and to be certain the center of the drill is not off side. This Instructable will show how to make a simple, inexpensive low tech guide.
- Stick of wood
- Machine screw
- T bevel square
- Drill with a brad point (drill) bit
Step 1: 59 Degrees
Mark two straight lines on paper as shown at 59 degrees. General purpose twist drills use a 59 degree angle.
Step 2: Transfer and Mark the Angle
Use a T bevel square to transfer the 59 degree angle to a square piece of scrap wood. I am using a piece of hardwood from an old cabinet door. It is 5/8 inch thick. I will be using an 8-32 machine screw, so I selected a drill just a little smaller so the threads on the screw can catch in the wood as if it were a nut. A brad point bit is easier to start precisely when drilling at an angle. The drill is handheld, so I used my eyesight to align the drill with the 59 degree guide line as best as possible.
Step 3: Insert a Screw and Check
I inserted an 8-32 machine screw through the piece of wood. I doubt I will ever sharpen a drill larger than 5/8 inch. Select a screw long enough to come through the wood half the diameter of the largest drill you expect to sharpen.
If the angle of the screw is not close to the guide line, drill another hole and try again. (The line and the screw appear poorly aligned in the photo. But, I stood directly over both and placed a straightedge on the line. It and the screw are quite well aligned, despite how the photo appears.)
Step 4: Using the Guide
The threads on the screw are close enough together to use as a straight line to check the grinding angle.
Turn the screw so something fine, whether the end of the screw or one of the threads aligns with the web at the center of the drill. As you grind the twist drill to sharpen it, turn the drill one half turn to see if the web aligns with the marking point you chose on the screw. If the web does not align with the mark you set, grind a little on the short side to lengthen it and to bring the web into the center of the drill.
Step 5: Grinding
Here is a good video on sharpening a twist drill by hand. It is less than twelve minutes.
The photo provides an overview of the video. Begin by grinding the area on both sides shown in red. Raise the angle of the bit and grind the area shown in yellow. Finally, grind in a continuous motion beginning at the point farthest from the cutting edge and make a smooth grind that comes near to the cutting edge as defined by the blue lines. The video suggests grinding on the sides of the web to shorten or thin it some.