Reminds me of turning a 1" rod of 6060 in the lathe - dry as a bone -
and as it heated up Al expands and you cut more. Then you come off it
and it soaks into the chuck and air - shrinks back to where it was and A
slot I cut not a smoothing cut!

Al needs coolant and plenty of it to stay cool so it won't expand.

Martin

On 4/4/2013 2:06 PM, Cydrome Leader wrote:
I understand how much everything on a lathe, including the work can flex, but
this just doesn't make sense to me,

If I turn down say a 1/2 aluminum rod that's chucked and extends only a half inch
and dial in 0.01" of feed and measure the before and after diameter with a
micrometer the diamter decreases by 0.02" Perfect.

The part I don't get is if I take a smaller cut of say 0.001" it will remove more
than 0.002" of diameter. For example if I need to remove 0.003" of diameter,
feeding the crosslide 0.001" will come pretty close.

It only seems to happen with very thin cuts. I'm only turning the crossslide dial
in one direction- there no backlash weirdness going on.

Why might this happen?