myford super 7 problem

I have been doing a job for a friend on my super7 upon examination of the part I notice that I have a spiral mark on the job. This appears to be of the same pitch as the leadscrew and is quite marked despite the finishing cut being of only a few thou (.003). I have checked that the gib strips on the saddle and cross slide are properly adjusted. I have never come across this before . Any suggestions Gents? The steel I have been using is leaded free cutting 1 1/2" dia turned down to 25mm. The component is 248 mm in length held in 4 jaw with a centre in tailstock to support it.

I have a super 7 plus which had this problem.When I had it serviced by the two Myford fitters they couldn't suggest a cause.After crashing into the gearbox with my depth stop I wrecked my half nuts.I was lucky that I was able to buy new ones from a fellow member.Since fitting these the marks have disapeared so is this the possible cause of this threading affect ,it could have some swarf in the half nuts,just a thought.

Frank

A bent leadscrew can do this (assuming the cut was with self-feed acting). Mount a sensitive clock on the saddle, bearing on a vertical or horizontal guiding face of the bed, turn the leadscrew, and watch for indication of horizontal or vertical movement of the saddle, in step with the leadscrew turning. Not an unknown Myford phenomenon.

Thanks Gents

It has given me something to work with, I have to admit I have never been a big fan of Myford lathes. I acquired this one at a good price a couple of years back, it has been useful as a second lathe. I would normally have used my other lathe for this job but I had something set up in it so used the Myford, I wish I hadn't.

Loose headstock bearings can make patterns like that too. Adjustment is a bit tricky on Super 7s. There's a thread on here sbout it somewhere.