"Jim Wilkins" wrote in message
...
On Nov 28, 2:20 am, "Ed Huntress" wrote:
...

To get back to my original questions, that wouldn't work for the
home-built
lathe I'm talking about. The complication of holding the outer spacer, and
getting the expansions right, isn't something I think you could do as a
one-shot deal. And the concrete head would add to the differential-spacing
woes.
Ed Huntress

But if you built it yourself and are the only user you know you have
to pay extra attention for problems. You could file the left-hand
bearing seat on the spindle to a moderate press fit so it can slide if
it has to, or not run it long and fast enough to warm up. You could
rub some wax on the spindle nose and shut off if it melts and turns
shiny.

Right. But if the bearing slips, you have no Z-axis stiffness. The spindle
would slide in or out when you took facing cuts or faced the back of a
bearing retainer or whatever on a shaft.

The traditional setup, with two facing, angular-contact bearings at the
front, and one floating bearing at the rear, solves all of those problems.
There isn't enough space between the front bearings for thermal growth to be
a problem. And both thrust loads, Z+ and Z-, are taken out at the front.
Then the rear bearing can float a bit with no loss of axial stiffness. It
needs to be preloaded in the radial direction to maintain radial stiffness,
but there, too, there is more room for slack than at the front.

Prototypes are full of gotchas and caveats but they still work well
for the people who built them. You might have to hire (or be) a tech
writer to put together a lengthy manual so someone else could safely
use the machine.

jsw