Working on my South Bend 9C

[Golem Pens]

Can you describe what the two placements are? Earlier, I thought you said rotated 180degrees apart in the collet. But it's hard for me to conclude that is likely a mandrel problem.

All of the A/B tests have been with the mandrel rotated 180° in the collet (and trying to keep the collect in the same position within the collet chuck, but that is a variable.

What would help narrow it down further? testing at more rotation angles?

 

[Susquatch]

What would help narrow it down further? testing at more rotation angles?

Yes, that would help. Especially if it repeats with rotation angle. Every 45 degrees would be adequate and fairly easy to do.

You should also check it up next to the collet.

As @jorogi suggested, manually turning the chuck is sometimes more consistent.

 

[Golem Pens]

As @jorogi suggested, manually turning the chuck is sometimes more consistent.

Oh I thought he meant the opposite, my first go was manual.

Every 45 degrees would be adequate and fairly easy to do.

You should also check it up next to the collet.

Time to make a spreaaaaaadsheet! Hooray!

 

[jorogi]

Oh I thought he meant the opposite, my first go was manual.

Sorry, I was referring to your youthful exuberance spinning the chuck 😀

 

[Susquatch]

@jorogi - you have a good point. But not only young guys - also old ones.

@Golem Pens - only testing can show what is best. On my lathe that has a very strong spindle and a minimum speed of 70 rpm, manually turning the lathe in neutral gear gets the best results.

Yours may not be the same. Furthermore, manually turning it in different belt positions (or even belt removed) might show better results.