Bob La Londe wrote:

I was just reading the manual (thank you Carl) for the new to me (ancient)
HF lathe and it says to fill the head stock with heavy weight motor oil.
I would think something like 80-90 gear oil would be better rather than a
motor oil. What do you think?

P.S. There is about an inch of oil in the bottom of the gear case.
Probably hasn't been full in a very long time.

I dutifully changed the oil in my Sheldon R15-6, which has a HUGE
D1-6 spindle. The chuck-end bearings are quite large, maybe
5-6" diameter ball bearings. The lube plate and manual said to use
Vactra heavy, but as soon as I ran it, the bearings started running
quite hot. After some online consultation, it became apparent it was
a typo, and they meant VELOCITE heavy, not Vactra! I put some
Velocite #2 in it that I had on hand, and was the specified lube for the
high-speed spindle, and it is working fine.

So, if your lathe has fairly large bearings, and is capable or running
at 1000 RPM or more, then you really want to use a light lube to
keep the bearings from running hot.

Jon