homemade device for mig welding small tanks.

I need some advice on building a device to rotate tubing slow enough to mig weld on endcaps. I am working with 3.5" carbon steel tubing .083 wall 14 guage. I bought a setup off ebay that I planned on putting a lathe chuck on but it doesnt work very well. Its a 110v gearmotor with foot control. Problem is is doesnt rotate slow enough rpm. And when turned down as slow as it will go it kind of jumps.Has anyone built a devise like this that works well? I need to start over with a better plan. Any and all advice is appreciated.