Carpentry, Crafts, Home, Repairs

Make your own custom precision drills and cutters

make your own custom precision drills and cutters

Sometimes when you’re working on a project, you don’t have exactly the right tool for the job. But often you can improvise something that works perfectly. Follow our guide to make your own custom precision drills and cutters.

While working on my DIY CNC machine, I wanted custom bearing blocks for the leader I was to fabricate with rods. The rods were stripped from printers and scanners purchased in a (typical for me) asset recovery sweep from dumped technology. They were just perfect for the job because they were precision ground, polished — and, of course, free. 

Problem was, they were 9mm in diameter, and I have no metric drills, let alone metric reamers, but my personal mantra is “Improvisation, Adapt, Overcome,” and so here’s how I solved the problem.

Make your own custom precision drills and cutters: the steps

Short sections of the desired bar stock are enough for some simple operations to form the bits. Since I wanted to be drilling plastic, and only a few holes, it was not necessary to harden the tools. However, if you are looking to drill something harder, or have many holes to drill, it’s wise to go through a hardening process.

This is one of the simplest forms of a drill, commonly called a spade or paddle bit. It is very easy to make, as you simply cut a flat section over the face of the rod about 40% deep. And you do not need to round off the edges. A lead-in bevel or “cone” on the business side is fine and should be done before the face grinding. Grinding away too much face reduces the effectiveness and precision. I used my double grinder and often quenched the bit with water to keep it cool while working on it.

This tool is even easier to fabricate than to restart the drill by simply chamfering the point and using a cold chisel — one stroke quite hard — to introduce a disturbance of material inline with the shaft. Slightly off-center becomes bearable, but keep it to a minimum. This bulge is actually going to do the tiny hole over-sizing necessary to allow a slip fit from the shaft strand. 

If it produces a hole too large, drag a file over it to reduce the hole to the desired size. A cold chisel removing a little in a series of hits may also be sufficient.

After good shop practice, we bored and reamed a piece of scrap first to test their suitability for application before laying down the actual workpiece. Starting with an undersize hole — in my case, it was 11/32 “(8.73mm) diameter — followed by the spade bit, then the drill tool … I found here with trying it, then trying for fit and repeating, Until I got the wave motion, which I wanted, that was sufficient. A drilling machine is very desirable for this low speed job, but careful freehand drilling can also carry on the day.

The CNC carriage system driven by the positioning system is quite nifty. I bought a thick plastic chopping board from the thrift store for the princely sum of $1 as storage for the no-lube housing.

This method worked great for my needs, and probably useful for other guided motion projects. For example, you can find robotics, 3D printers, pumps and linear and rotary motion applications where a low-cost precision build is desired.