While working on my DIY CNC machine, I wanted to fabricate custom bearing blocks for the guide rods I was using. The rods were stripped from printers and scanners acquired during a typical- for me- asset recovery sweep, and were just perfect for the job, being precision ground, polished, and of course free. Problem was, they were 9 mm in diameter, and I don't have metric drill bits, let alone metric reamers, but my personal mantra is :"Improvise, Adapt, Overcome", and so here's how I solved the problem.
Step 1: Cut Some Blanks
Short sections of the desired rod material will suffice for some simple operations to form the bits. Since I was going to be drilling plastic, and only making a few holes, it wasn't necessary to harden the tools.
Step 2: Grind the Cutting End of the Drill
This is one of the simplest forms of a drill bit, commonly called a spade or paddle bit. It is very easy to make as one simply grinds a flat across the face of the rod approximately 40% deep, taking care not to round over the edges. A lead in chamfer or "cone" at the business end is o.k. and should be done before face grinding. Grinding away too much face reduces effectiveness and precision. I used my bench grinder and frequently quenched the bit to keep it cool.
Step 3: Form the Reamer Flute
This tool is even easier the fabricate than the drill bit, again begin by simply chamfering the tip, and using a cold chisel strike once, a fairly heavy blow to introduce an upset of material inline with the shaft. A slight angle off center will be tolerable, but keep it to a minimum. This bulge is actually going to do the miniscule hole oversizing needed to allow for a slip fit of the shafting. If it produces a hole too large, draw a file across it to reduce the hole to desired dimension. Absent a cold chisel, a prick punch applied in a series of hits may also suffice, but I have always had a chisel at hand.
Step 4: Test Cut and Final Plunge
Following good shop practices, bore and ream a piece of scrap first to determine suitability for the application before committing the actual workpiece. Begin with pre- drilling an undersize hole, in my case it was 11/32" ( 8.73mm) dia. This was followed by the spade bit, then the reamer. Here, technique counts and I found using a pecking motion, trying for fit and repeating until I got the shaft movement I wanted, was sufficient. A drill press is very desirable for this job using it's low speed, but careful freehand drilling may carry the day also.
Step 5: The End Results
The carriage system driven by the leadscrew is so sweet, I used a thick plastic cutting board purchased from the thrift store for the princely sum of $1 as the stock for the no- lube bearings on all stations in fact; X,Y, and Z
Step 6: Parting Thoughts
This method worked superbly for my needs, and likely will be useful for other guided motion projects such as found in robotics, 3D printers, pumps, as well as linear & rotary motion applications where a low cost precision build is desired.