I have been looking at the following 4th axis which seam to be pooping up on ebay and was wondering if anyone had considered mounting on to the bottom of a vertical z axis and replacing the chuck with a 2.2kw spindle mounted in place.

Does any one have any thoughts to this? im wondering if the shaft will be stiff enough?

best regards

CNC Router Rotational Rotary Axis A-Axis,4th-Axis 50MM Chuck Engraving Machine | eBay