Acme thread

[SAISAY]

Hi again,
I need to get a new lead screw, the old one is fishtailing although the engineer says it is straight. I put a round file in the chuck and it did not fishtail, I have no idea why it is happening but it is ruining my cuts.
I can measure it as 0.5" x 8 tpi.
My problem is, do I call it 0.5x8tpi 2 start or do I divide the threads with the starts and then get 0.5"x4tpi 2 start?
TIA

[Bob Willson]

Hi saisay
If you have to get a new lead screw why not get a proper ball screw?
For a ball screw and the nuts and end bearings, it really shouldn't cost too much and you will get MUCH better performance and accuracy.
I am assuming that this is for the Shark, or have you also got yourself a lathe?