"Ed Huntress" wrote in message
...

"Jim Wilkins" wrote in message
...
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.

Well, surface finish can go to pot when speeds are too low, and the
variation in speeds across a large face is one of the classic problems in
machining. When CNC came in, a very big deal was made of the fact that you
could program for constant surface speed to overcome the problem.

In some old textbooks you'll see different comments upon it, one of which
was a suggestion to preferentially cut from the center out, adjusting
speed for the minimum that would give you a clean cut near the center and
counting on the heat tolerance of HSS to carry you through to the outside
diameter. This is iffy, of course, but it's the way it frequently was done
in production, back in the days of HSS tools and manual machines in
high-volume manufacturing.

I don't think there's any really good solution with a machine that can't
change speeds during a cut. It's been a while since I read the old
articles and books that talked about it but I don't remember any clear
answers. I've run into the problem myself, which was one of the first
things that motivated me to try using brazed, carbide-tipped inserts on my
old South Bend. They handled it pretty well, especially in cast iron,
which was giving me fits.

--
Ed Huntress

some times its the metal...

I got some metal that welds real good, but turning/milling no good, as the
engineer at the steel place, where I bought it, "that stuff don't machine
very well, but welding is good"

So, its kept separate from the other metal.

xman