Making custom drills

Making Custom Drills

I often need to drill holes in brass and plexiglass. Since I do not wish to reshape all of my drills, I like to custom make spade drills as I need them for such jobs.

Please know that it takes less time to make each drill that it takes to look over this web page.

I try to keep on hand a small assortment of several diameters of HSS drill rod blanks for making these custom drills. By using HSS, I do not need to worry about hardening or tempering the steel once ground to shape. This is critical.

The sample drill shown below was ground to shape on a Gorton 375 grinder. Any tool grinder should easily do the task. The Gorton grinder uses 4NS collets. A few are shown here.

Whenever I grind drills, I try to do several at the same sitting. Below are four awaiting grinding.

The tool holder was set to a 5 degree angle.

The angle may be seen below.

The tool holder index was set on one of the "4" marked holes. These are set at 90 degree intervals for such jobs.

The first grind looked like this.

The depth of this grind is controlled by the feed dial.

After this grind the tool was flipped to the opposite "4" on the index plate.

Here the opposite side is ready to be ground.

After grinding to the same depth, the drill now looked like this. It should be symmetrical.

It was now time to grind the point angle. I set the angle to approximately 59 degrees.

Before grinding the point angle, the drill must be rotated 90 degrees (to the adjacent "4" on the index dial).

This put the drill in the position shown below.

The first half of the point was ground a little past center and the feed dial reading noted.

The drill was next flipped 180 degrees to grind the other point angle half.

Looking down on the drill point end, it will be noted that the grinds meet in the center.

The drill has no clearance at this point. To grind the desired clearance, the collet is loosened and the drill rotated clock-wise about 5 degrees.

The point clearance is ground just like the point was - a little past half, feed dial position noted, drill flipped 180 degrees, and ground to the same feed dial reading. Once the burs are scraped off with a finger nail, the drill is ready to go to work.

Here are two completed drills. Notice the slight angle at the very tip of the drill where the clearance grinds meet.

One very big advantage of such drills is that the tips may be stepped down to any required diameter.

These drills are self starting and do not require a center drill hole. By leaving the sides of the drill full diameter, the drill may be touched up to resharpen it hundreds of times. Such drills are great for drilling lantern pinion holes on clocks. Clean the chips out of holes often when using these drills.