I have experienced this problem before and it turned out to be crossfeed
leadscrew alignment. Make certain that the follower nut is loaded evenly
from one end to the other end of crossfeed travel and that the resistance to
turning the dial handle doesn't increase when the crossfeed clamping screw
is tightened to the follower nut. Any aberation in the crossfeed travel will
show on the facing finish. If the problem only shows when power feeding and
not in manual feed, then look at the apron to crosslide fit for drive gear
misalignment/binding.
Steve

"HeffaLump" "Percussion Engineering" wrote in message
et...
I've developed a problem when facing on my lathe, I do a lot of small dia
disks (20-40mm) in 6082 Aluminium and when it comes time to polish the
face I'm noticing concentric circles appearing on the finished surface.

They're not to pronounced, I'm able to polish them out easily enough, but
I'm worried it might be indicating a developeing problem.

I've tried cutting at 0.5mm down to 0.1mm with little differance both
manually & on powerfeed, I've adjusted to gibs to the cross slide (tried
it loose, spot on & too tight), varied the RPM's, differant cutting
tools/holders and I can see that the saddle isn't moving from the DRO.

I've put a dial guage against the surface with no discernable movement
when rotating !

The circles are easy to see but impossibly difficult to photo, you have to
catch the light just right but they appear to be 2-3mm apart. I cannot
tell if they are truly concentric or spiralling.

I'm thinking 2 things . . . either play in the head bearings or the
crossfeed leadscrew. Please don't let it be the head bearings but I can't
see how the leadscrew can affect the finish if the gibs are correctly
set????

Any ideas?