Hi Woody, I don't know your lathe at all but angular contact bearings are frequently set up with a "spring" arrangement to apply a defined pre-load to the bearings to make for a stiffer spindle. As such, your plastic spacer might be intended to collapse as the C-nut is tightened to provide this pre-load. A specific length can't be specified.

Cue all cl300m experts.

My experience:

Now remove the locknut and thread on the bull wheel, it will be apparent that the bull wheel no longer lines up with the tumbler reverse. I had to shorten the spacer by 4mm, which I did in the lathe, relying on friction to hold the rear race in place against the light load. Once shortened I had to use a rat-tailed file to enlarge the notch in the spacer for the end of the bull-wheel key, before replacing the rear bearing shield, fitting the key and bull wheel. I then refitted both lock nuts and re-tightened the mandrel. Appropriate preload for a roller bearing this size and precision application is very small, of the order of zero to four thous. The pitch of the mandrel thread is 1.5mm or 60 thou so, once all shake has been removed with the first locknut, tighten it by no more than a further 24 degrees and lock it securely with the second nut.

These might be helpful;

Parting Off on Mini Lathes and Bearing Choices

Changing the Bearings on a Mini Lathe

Slightly updated versions of my articles written about 15 years ago!

Neil

Posted by woody1 on 11/11/2020 20:14:02:

I bought my angular contacts…

Just checking – if woody1 is fitting A/C bearings, there shouldn't be any need to shorten the spacer, should there? The A/C bearings are supposed to be the same width as the originals, I believe.

Just re-make in metal to the existing dimensions? (My 7X lathe is a different make with a brushless motor, or I'd offer to measure the spacer!).