"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

Could be the carriage gibs are a bit loose- the carriage will wiggle on the
ways and plunge-lift-plunge-lift...

-Carl