Hello. I’m new to swiss machining and I could use any possible help. Would anyone advise me on how to correct roundness on machined pieces? They’re not coming out round. They are at least .0010” off - when I measure the outside diameter, one spot measures .2490”, and when I rotate the same piece ninety degrees, I’m getting .2500” OD. Obviously, they’re not perfectly round.

What would be the major factors that impact roundness? What do I look for? How do I fix this problem?

Thanks ahead.

There is a swiss machining forum on this site, that might be a batter place to look for help.... the guys there defiantely know their stuff :)


that being said, it sounds like your guide bushing isn't tight. If it's not tight, the material kinda "flops around" and causes what you are talking about here.... It's a good idea to use precision stock to make sure the guide bushing stays tight, otherwise you end up having to re-adjust the GB every bar to compensate for the varying sizes.

Also, make sure your tools are good and sharp and on center.... A tool too high can also make your parts not round.
I hope that helps!

I'd be willing to bet your stock is out of round as well.. a swiss can inprove the roundness of a bar by 70% at best, sometimes less than that, so if your bar is OOR by .002 I can see your parts being .001 OOR... have you tried using V anvil mics, I 'D be willing to bet there is some tri oval in there as well..

the cure, centerless ground stock with roundness specs to match the the roundness specs of your parts, we typically use from ±.0005 to ±.0002" on stock.