4th Axis running as CNC lathe using milling machine

[Jonathan]

My 500th post on this forum :surprised: ... something a bit different.

A few months ago I started making a 4th axis for my milling machine, or router. My reason for doing this is to have it belt driven, thus faster than the vertex rotary table I converted and capable of being used as a lathe. This is the original design:







It includes solenoids to make a disk brake which should mean I can get a much higher holding torque than with the stepper motor alone when stationary.
I machined the shaft and bearing housing at school since they were much to big for my mini lathe, and CNC milled all the slots for the solenoids using the rotary table. The hole through the spindle is 1". I press fitted the tapered roller bearing outer rings.





Recently I got round to making and fitting the timing pulley so I thought it was time for a test. I've not made the mount for any motor yet, so I just used the large brushless motor I'd converted to a spindle, put a pulley in its chuck, and stuck it in a vice. Crude, but it works for now. Shown below is it set up to machine the front of the spindle, the same as my C3 lathe, to fit the chucks I have. I left this bit until last since machining this in place should minimise the runout:





Spindle after machining:


The motor, though only run on 24V from some big batteries - not the 48V that it is rated for, and geared for 2900rpm works well at the much lower rpm required to machine the face of the spindle which is 80mm diameter.

At the moment my method for mounting the lathe tool is distinctly dodgy. Not surprisingly it vibrated a fair bit. At some point I shall make a proper tool-post that bolts onto the milling machine somewhere else, not to the quill.

Just as a test I tried machining a 22mm diameter hemisphere onto a piece of aluminium bar, and a similar size hemisphere on to the end of a 20mm diameter mild steel bar. I will upload the videos shortly, here's some pictures of the result. Not great, but it's hardly surprising with the way the tool was mounted and the tool I used:







The next stage for this is to make the motor mount incorporating brushless and stepper motor and probably a dual timing belt reduction to get around 10:1 ratio for the stepper motor. Then I will add the solenoids, if necessary.