Grind a drill correctly

Twist drills belong to the absolute basic equipment of a craftsman. The same applies, of course, to home improvement. However, sooner or later, after many operations, each drill bit gets to the point that it no longer drills sharp enough. Metal drills can then be sharpened. Of course, there are special grinding machines for grinding drills, but these are hardly worth buying for do-it-yourselfers. However, you can grind your drills yourself if you do not have a special drill grinder.

Distinction of drills

Drills are used for hand and boring machines to drill holes in a variety of materials. Accordingly, you can distinguish twist drills according to the material to be processed.

  • Holzbohrer
  • masonry drill
  • metal drill

The metal drill in detail

In the plan view you can see the two main cutting edges, which roughly correspond to the drill radius. At the outer end of the main cutting then makes a slight kink. This is the minor cutting edge, which is responsible for a good guidance of the drill. You also see a small cutting edge in the middle, that's the cross cutting edge. If no smaller hole is drilled, this edge first grabs while drilling.

Angle on a twist drill

The chisel edge is at an angle of 55 degrees to the two main cutting edges. If you look at the drill in the side profile, you will notice that the tip is converging. Here the drill forms an angle of 118 degrees. You can also see that the free space behind the main cutting edges is bent downwards.

The difficulty in grinding a drill

It is precisely these dimensions and appearance that make grinding a drill difficult. In a rotary motion on the trestle, you do not have to just follow the free surface, always keeping this surface straight against the grinding wheel. At the same time you must also bow the bow without accidentally grinding away the cross-cut edge.

Exercise is all about drill grinding

This makes grinding a drill relatively difficult. However, the grinding is only a matter of practice. You will see after a few drills that you grind that the grinding result is getting better and better.

Grind step by step instructions for the drill

  • drill
  • bench grinder
  • safety goggles
  • possibly drill gauge

1. Preparation

First put on the safety glasses. Place the main cutting edge straight against the grinding wheel. Support the drill with the middle and index fingers.

2. Grinding the drill

Now start with the grinding. You turn the drill clockwise with the spiral (which is also the drilling direction), at the same time you pull the drill upwards. Only then can you achieve a straight cut with a curved open space.

3. Check the drill bit

Now you can create the drill gauge and first check the point angle. There is also a measuring scale on the gauge. Both main cutting edges must be the same length. This is the only way to ensure that the chisel edge is actually centered.

Tips & Tricks

If you do not have a drill gauge, use two appropriately sized nuts and place them side by side. The converging surfaces form an angle of 120 degrees. So you can check the correct angle (118 degrees).

Rub an old piece of wood or metal sheet with chalk and set it upright. Before that (one, two centimeters distance) mark a point. Place the drill with the tip up and the first main cutting edge facing the plate. Then draw a semicircle like a circle. Repeat the process with the second main cutting edge. If the drill is ground correctly, you will not see any offset on the chalk.

Swing the drill gently over the grinding wheel disc during grinding. Press the drill too hard, it glows and is no longer usable. A cooled and annealed drill can be recognized by the shimmering blue surface.

Video Board: How to Hand Sharpen a Twist Drill