Fourth Axis... Thoughts?

thinking about buying one of these

CNC Router Rotational Rotary Axis, A-axis, 4th-axis,3-Jaw and Tailstock | eBay

intend to engrave on the edge of fruit bowls (turned seperately on wood lathe)

Thoughts? for... against...

They are shìt.

Look nice but they are just driven via a timing belt to a straight thru spindle.
OK for engraving on wood or candles [ unlit ] but if you try to use these in anger the cutting forces of a decent cutter will force the drive backwards.

If you want a decent 4th axis then get a decent rotary table and fit a stepper motor to it. Because it has a 72:1 or 90:1 worm reduction it cannot be reverse driven.

I agree entirely with John S - a timing belt, particularly a small one like that, is not much use for a 4th axis since the stiffness of the belt is too low. Unless you want to splash out on a harmonic drive (eBay), then a rotary table is a good way to do it.

KC

I agree with Jon that it would be suitable for your intension. Don't waste your money though, a couple of Pillow blocks and a cheap chuck, a bit of round rod and a backing plate for the chuck would suffice. If you want to do more with it though hi torque and sensible gearing is required. Harmonic dives are out of reach for most people unless you are lucky on the bay.