edge finish - ripples and ridges

[Jonathan]

That's a clear example of trying to cut faster than the machine, or tool, is good for. The wavy lines could also be caused by severe resonance ... either way a finishing pass would have sorted it out.

I could skim the parts for you, but it's not a quick job unless they're quite small.

I have a bearing housing which seems to be the correct diameter if measured across x axis, but 0.1mm smaller when measured across y axis. What would cause such an error? runout on a lathe? it simply seems elliptical rather than round.

Backlash, or more precisely - greater backlash in one axis. Bearing housings should really be bored, not milled, since even if you have a rigid machine with zero backlash the pocket will end up something other than a circle. The bore doesn't have to be out by much for you to either just have a loose fit, or worse distort the outer ring of the bearing causing it to wear prematurely. If I'm cutting a part on the CNC Router which includes a bearing, then I generally either bore it completely on the lathe or if it's a big bearing mill the pocket to 0.5mm undersize and then bore it.