Originally Posted by
wizard
Interesting project Kyle, I'm a little late to this thread but what can I say it is summer and I have more projects than time.
As for the ball nut there is no way to tell for sure if it will fit the lead screw. You would need to know the lead screws pitch and the number of starts to begin with. beyond that not all manufactures roll their ball screws with the same dies so if the brands don't work together you are screwed again. If you don't know the specifics of the parts you are replacing sometimes it is easier to just order the ball nut and screw complete. The old nut might be helpful if it was stamped with model and manufacture info.
The type of couplings you posted (sometimes called Lovejoy couplings) are not ideal for CNC work as the generally have some backlash. There are variants that claim to be zero backlash but generally I think you are better off looking for a different solution. One possibility are Oldham couplings that still allows you to buy shaft fittings with differing ID's bored in them.
As for the LabVolt machine glad to see you reconditioning it. The last I heard of anything with the LabVolt name stamped on it was like 41 years ago when I was taking some tech classes. Those where electronics trainers and to be honest I wasn't left with a very positive opinion of the company and its products. Hopefully their CNC is of better quality.