Bob,
It would be very helpful to know what you are cutting, the surface speed,
the tool shape, the lathe you are using and whether you are turning a
diameter or facing. I am not being difficult, but there are literally a
myiad of possible causes. For my first guess, I will assume you are turning
a diameter and the fault is chip clearance. The cut chips are being trapped
between the back of the tool and the work and actually cutting the already
turned work surface. This is very common and incidently the number one
problem in machining anything on any kind of a machine. (CHIP CLEARANCE) The
problem is exasperated by the fine feed and insufficient tool clearance.
Here is a good rule, the width of the cutting surface on the tool nose must
equal 1.5 to 2.0 times the feed speed and use as much space between the work
and the back of the tool the job allows. It is a misunderstanding to think
that the finest feed equals the best finish. Remember, the finer the chip
the easier it is to get trapped between the tool and the work.
Steve

"Bob Engelhardt" wrote in message
...
http://home.comcast.net/~bobengelhardt/RippledCut.jpg (90 kB)

I was trying out some bits that I had just ground & fooling around with
the independent feed on my lathe when I got this strange ripple pattern.
The ripple peaks are about .030 apart, but the feed was only .002. And
the ripples are rings, not a helix. It's mystery metal.

I'm speculating that there is a rub-then-cut kind of oscillation going on.
That is, the .002 feed is not enough to get a bite on the steel, so it
rubs a while, without cutting until enough advance occurs then it
bites/cuts until the pressure is relieved and goes back to rubbing again.
Does that sound right (it's not real clear how that would give a ripple
pattern)?

If so, is there a way to avoid it? I thought that I had the bit pretty
sharp (it was just a plain RH roughing bit). Could it be lack of rigidity
in the lathe?

Thanks,
Bob