Driveshaft shortening and alignment jig - video

Driveshaft shortening and alignment jig. By Chuck Bryant. 9:07 video:

https://www.youtube.com/watch?v=fgHyLf7t37w

Having shortened and lengthened many driveshafts, I would have to say that only addresses the axial alignment, critical alignment is maintaining the existing phasing of the u-joints. On those that could be accommodated in the lathe, a longitudinal tool-mark scribed along the DS & relevant yoke is the easy way. Others like the DS above, needed mandrels through the u-joints, secured to a tee-slotted plate which allowed for adjustment for length...
Over the years I was brought quite a number of driveshafts to rectify balance issues, without exception, the problem lay in out of phase u-joints.
That I had a 4-1/8" spindle bore lathe, at the time, was a boon...:-)

Use a piece of steel angle in a jig for welding and alignment of round bars, shafts, and pipes.