When experimenting with new materials on DIY CNC machines, it is often easy to break perfectly good and even brand new CNC router bits. This occurs even more so when working with small diameter CNC cutting or engraving bits.
We all know the feeling. You know you’re pushing the feed rate just that little too hard, but you think you will get away with it this time…. and then…. SNAP!
Recently while cutting various projects from foams and plastics, I had a brain wave. Shortly after breaking a second 1mm diameter End-bit while testing the feed rate on a plastic cutout, I wondered if the quality and sharpness of the bit actually really mattered for the lightweight materials I was working with. Super sharp CNC cut edges are not always necessarily for many of my projects anyway. Any rough edges left over can easily be cleaned up with light sanding afterwards.
I had many old, broken CNC bits laying around the workshop. I took a pair of vice grips and allowed one of the old CNC shanks to meet the electric bench grinder.
In seconds, I had a brand spanking DIY one fluted CNC bit completed. Just by roughly grinding off a half face from the old 3mm shank. I tested the new DIY bit on a 2mm thick sheet of acrylic plastic. To my total surprise, the cut was absolutely no problem at all! It was definitely no problem for softer foam board material.
I then got a sharpening stone out and spent a few seconds sharpening up the cutting side edge of the half shank I had made. I also cleaned up the trailing edge burr left by the grinder. The result? Even better, cleaner cuts!
I had smooth, good quality cuts from my CNC machine and well defined, sharp edges on any fine engraving and surface work. In most cases, I couldn’t tell the difference between the cut results of my newly made DIY CNC bits and that of brand new, professionally produced cutting bits straight out of the packet. I was stunned! How could I have been this naive all these years?
After rummaging around for more broken hardened carbide drill bits in my workshop, I got a little more creative with my new found success. I went on to attempt grinding down more bits to make V bits, End bits and Ball Nose bits. These bits all worked relatively well too.
For foam board cuts, I later found that I didn’t need any hard grinding of the shank surfaces. Just a very light roughing on the outer surface was enough to make them perfectly adequate for cutting.
OK, so this may not be a solution for the professional who is proud of their high priced workshop tools and quality standards, or the CNC hobbyist who is cutting long and repetitive projects requiring speed and longevity from bits. But for the occasional DIY CNC hobbyist banging around in the back shed, I believe this is a great idea! It has already saved me a load of money, considering the cost of replacing broken bits and the fact that I could reproduce very similar cutting results with my DIY bits anyway. The idea is so quick and simple. I just hadn’t thought of it in the past.
I hope this idea helps others who are running on a tight CNC budget, or those who have just broken that last cutting bit minutes before the hardware store closed for the day. Give it a try!