These are pictures of the Weld Positioner I built from parts from 
Boeing Surplus.

The variable speed reversible motor unit goes from 0 - 122 rpm.
It has a small flex-shaft that goes to an external speed control wheel.

The worm gear box has a 40 : 1 reduction so the output is really 0 - 
3 rpm which is perfect.

I lucked out in that the motor has a 5/8" shaft out, and the worm 
gear has a 5/8" input socket.

The tilt system is a valve closer from a 6" pipe valve.

The flat platen is a jig plate I found at Boeing Surplus.
I just bolted a plate to the back and welded on a 1" shaft gear 
sprocket  so it can mount to the 1" shaft of the worm gear box.

The chuck is a 6" lathe chuck, bolted to a plate with a 6" length of 
4" pipe extending it out from the worm gear shaft.
This allows me to pass things inside the chuck.

Grounding is achieved by clamping the ground clamp the  bronze sleeve 
pressed onto the back end of the gear box shaft.

Eventually I will add a motor brush grounding widget, but this works for now.

The unit weighs around 100 lbs.