Spirals vs even fill in a circle


I’m testing the machine on aluminum and use a circle shape /fill for that. Bit used is 1/8 ball-end carbide mill bit. properties are set accordingly. Instead of a smooth milling I get spirals. Am I missing something?


How flat is the bit head?

Thanks for your replies. Adjusting the stepover to 10% resulted in a more or less flat bottom. I can still see some grooves though. Please see below a representative image and the photo of the bit used. What, do you think, is causing the grooves?
UPDATE: I figured that spirals appear when going outward from the center, during the inward carving I get a very smooth cut.