Benchmaster

[34_40]

Are you actually looking at the bearings to get the numbers or did you get the numbers from a book or manual?
I know you have enough experience to diagnose what is happening.. and enough experience to know when a bearing is to hot!!
Perhaps a previous owner installed new parts but with the wrong pre-load.?  That would be my current guess.

[chips and more]

Doing 15° after touching is not really definitive. I would get the pitch of the thread and math out the angle that would give me about 0.002” more smash/pre-load.

Trying to remember LOL. The last time I did this was on my surface grinder. It had fine threads (can’t remember what pitch) and I did like 5°. And the grinder has been very happy for years now. And I use 10w oil in the spindle.