Making a CNC Milling Machine

When I retired from work a couple of years ago, I decided that I needed to embark upon a completely new hobby, and preferably something that exercised the grey matter a well as keeping the fingers busy! As a youngster I loved making things with Meccano, so it wasn’t long before I hit upon model engineering. With no experience whatsoever, and a non-engineering background and no tools it has been a steep learning curve, but I soon realised that the way forward to equip my workshop and not suffer terminal wallet pain was to make as much tooling as possible myself.

I made a Sterling engine and a couple of other bits, including a fixed steady, tool height gauge, small and large boring bars, quick change tool holders, keyway cutter, spherical cutter, centring microscope and dividing head. I realised that the wear on my old Myford lathe was causing some problems, particularly the backlash on the saddle adjustments and solved this absolutely by fitting a digital readout.

Then I thought a good challenge would be a clock, however the design I chose, published in “Model Engineer” required the cutting out of curved pieces for the clock frame. Thus the notion of Computer Numeric Control, or CNC for my mill became a necessity. I soon realised that to purchase a ready made machine was beyond my means, so the DIY option was the only way forward. My mill is imperial, and one turn of the table handwheel moves the bed by 62.5 thou, so it was logical to arrange the drive with a reduction of 6.25 to 1 so that the motor rotates once to advance the table by 10 thou. This is a convenient ratio, achieved very simply by two reductions of 2.5 to 1. Toothed wheels and belts seemed the obvious way forward, and it was easy to source wheels with 50 and 20 teeth.

The only major problem I encountered in constructing the gearbox was belt slippage, not prevented even by extreme belt tension. Once again the answer turned out to be very simple - a roller keeping each belt fully in mesh. I bought the control boards and stepper motors reasonably priced on ebay, and now have a functional and very accurate system. The next challenge is the z axis, raising and lowering the mill cutter!

The video shows the CNC milling machine in action cutting out the clock frame - hit the play button in the bottom left of the video to start watching