I ran into this by accident a few weeks ago. I was making a handwheel for an
Atlas milling attachment from an aluminum blank. The OD of the wheel turned
out with that 'torn' finish. But it was uniform, looked OK, and offered a
superior grip that let me set the gibs a little tighter than usual. So I
left it that way.

"Phants" wrote
That description is usually caused by metal being "pushed off" or "torn
off" rather than cut off. The tool being too low (work attempting to
"ride up" onto the top of the too bit) or too high (rubbing under the
cutting surface) produces this. I have also seen this happen with a
"negative rake" on the top of a fairly flat cutting surface.

Remember this for the time you want a (small o.d.) surface to grip with
your fingers to turn and do not have a knurling tool... Tear it out
(it's sharp) then file off the tops of the points ... Not for clients or
others but quick and dirty in your own shop - and cheap...!

JHbs