Miniature 4th Axis

Newsflash: I used it for something useful, check out the hub on the nautilus page

I decided to make a CNC controlled dividing head for my Proxxon mill. There are no suitable tables readily available due to the small size of the mill so I had to build it from "scratch". As luck would have it I was given a small worm drive gearbox made by SH Muffet it has a gear ratio of 60:1 which is a touch low for some gear cutting applications but I don't intend to cut gears. Plus, at the small sizes I am machining 24,000 step resolution should be good enough. As for backlash, it does have some although Muffet do do anti-backlash versions of their gearboxes. I intend to drive it in one direction only and suspect that for most machining it should be fine.

Above you can see the tiny gear box as well as the even tinier NEMA11 stepper motor used to drive it. An aluminium bracket holds the motor in the correct alignment and a piece of flexible PVC water hose couples the two. The coupling is to be replaced at a later date with an aluminium one as on the x,y,z . The two chucks shown are from Clisby who make a tiny little lathe (which I also intend to convert) The 4-jaw was all they supplied when I bought the lathe but now this scroll three-jaw chuck is available. It is a nicely made chuck, better than the 4-jaw (and more expensive) and should be good when using round stock to produce parts.

The jaws simply screw on to an adapter I made from steel. It has a 1/2" 20TPI thread and is secured onto the gearbox shaft with a set screw, although I may change this to a rolled pin going through the shaft. I expect to mill Delrin, wax and foam mainly so perhaps it will not matter in the end.

I also bought a faceplate to further increase the workpiece mounting options.

Vital statistics:

Resolution: 24,000 steps per revolution (400 steps(half stepping) X 60) or 0.015 degrees

Chuck diameter: 40mm

Centre Height: 37mm

Thought I should post a pic of something, here is the mill milling sphere of sorts. I have also done some nice engraving, you simply draw in 2D and set the rotary axis up as a linear one. Then ensure that the steps/mm correspond correctly so that the length of the picture/text to be milled produces 360degrees of rotation. I'll try and find a pic of that, the main trouble was actually the Clisby 3 jaw chuck there is no taper so it doesn't centre on the adapter properly. May have to add a small taper to both.