On Fri, 12 Sep 2008 15:04:32 -0700 (PDT), Jim Wilkins
wrote:

On Sep 11, 7:44*pm, "Michael Koblic" wrote:
If you are facing a 5" diameter work in a lathe do you increase the RPMs as
you near the center?

--
Michael Koblic,
Campbell River, BC

I've never seen a problem when cutting at low speed with HSS.


The specific problem tends to be that, if you are using carbide or HSS at high
speed, you can get a beautiful finish on the outside. Swarf coming off yellow
or blue (for carbide). At some point towards the centre the speed will fall
into the region where the Built Up Edge phenomenon occurs. The surface finish
will go to hell during this range. As the tool gets closer to the centre the
finish will still be bad, because there is a rough gob of steel welded to the
tip of the tool.

Running HSS below the BUE region all the way will avoid the problem, but can
still benefit form changing the speed as the cut progresses if possible e.g.
from maybe 50rpm at 5" to 250 at 1". This is easy if you have a variable
speed drive. It's a waste of time if you need to do belt changes.

Running carbide above the BUE region can get a bit scary towards the centre of
the part :-)

PS. The best way to get a nice finish is to slap the part on the surface
grinder after facing BEG

Mark Rand
RTFM