On Sep 13, 7:37*pm, Mark Rand wrote:
On Fri, 12 Sep 2008 15:04:32 -0700 (PDT), Jim Wilkins
wrote:

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.

That's what I've seen, too, but I'm not sure enough of the details to
post them for posterity. I try to keep the speed below yellow chips
with HSS and up in the blue chips with carbide. If you stop to change
belt speed the bit will leave a ring on the work. Good HSS will take
the heat. A lot of my bits are Medium Speed Steel from Enco, which at
least are easy to grind.

With practice I've learned how to recognize and mostly avoid built-up
edges and their rough finish. In general I think it's from following
the bit grinding and honing instructions in old lathe manuals and
water-annealing bad steel.

For some reason facing out seems to leave a better finish. Maybe it
has to do with wear and play on my 1965 lathe, or because it's a shear
cut.

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

Before I bought one I filed and sanded out the tool marks with a
single-cut pillar file and fine SiC paper on a steel block. The amount
of work involved is -why- I bought the $100 worn-out surface grinder,
which has been very useful for finishing and for sharpening tools.