That should be fine to give you smooth enough arcs so it would seem it must be mechanical if your code is a true arc, it could I suppose be you need a wider pulse but unlikely as you would notice this all the time.
 Can you post a pic of the rough arcs?
Hood

Well i have the G540 and like many others, I was having problems losing steps in the Z axis. I've read that using sherline mode fixes this, which it did. Now from my understanding all sherline mode does is increase the pulse width to 40micro.

Anyway, as for the rough radius, I think it was just the material i was cutting (cast tool and jig plate) because i ran some normal 6061 Aluminum last night and the radi's look fine.  Its a mystery

SScnc

 to jump your thread for a moment. do you have a good source for your cast tool and jig plate material . is their a chance for your supplier info.

thanks bill

check out www.speedymetals.com

It is kind of hard to find within the site, so click on aluminum then plate, and its under there.