"Kelly Jones" wrote in message
....
Hi all. I just got a new lathe for Christmas and I have been trying
it out.
I have been trying to turn a piece of unknown CRES from about 0.75 OD
to
about 0.38 OD. I have tried various speeds and feeds but still keep
getting
a very rough finish. The finish is so bad that it looks as is the
metal is
being torn rather than cut. The surface is full of small slivers that
would
cut your hand i a heartbeat. I am having similar problems with an
unkown
carbon steel, although not as bad. I have checked the Machinery's
Handbook,
the Army metal working PDF, and some engineering reference books I
have, but no help. I thought that I might even be using the tools
wrong
(cutting on the wrong face) but I can't seem to find the source of the
problem. The lathe is a Grizzly 12 X 36. Any ideas?

Hi Kelly;
The speeds, feeds and the amount being cut will all have an effect on
the surface but those are probably not the problem.

Do you have a bench grinder for your tool bits?

Two points:
1) line up the tool bit (where it is cutting) with the exact center of
the piece being turned. You can see this by taking a "face cut" - if you
are low you will see a little round "stub" when your tool bit passes the
center and under it. Shim the tool bit up repeatedly until the cutting
point passes thru (or almost) dead center. (better to be a few thousands
low than high - if high the "relief" or under side will be "rubbing"
rather than cutting)

2) Find a reference on the angles you should grind on the tool bit. In
general the softer the material, the sharper the angles. Also check the
rasdius at the cutting point - anywhere from a "hand stoned" very slight
radius to large "form tool" for a radiused shoulder on the work.

What you ask is not really "simple" and you will still be learning these
operations next year. You can learn about your "speeds and feeds" (for
each material) from the colors (steel) on the continuous "chip curl" -
or the small separate chips that fall to the bed... Aluminum will curl
and spiral or be in ling straight "strings."

I suggest you find a machinist, toolmaker or modelmaker in your area
that will let you watch and ask questions as he demonstrates - You will
learn more it two hours that way than with all the instructions - then
read the tables and instructions and play... You're going to love
this...
JHbs