Depending on your tooling available, I would use 1/2" to 3/8 dia cutter for this.The bigger the cutter , the more load the machine is withstanding.I'd use a 2 or 3 flute UPCUT. downcut if you are worried about holding the part down. 90 % of work is milling various thicknesses and grades/ speicies of plywood. no need to depth cut. Ramp in at 30 degrees or somewhere around there. RPM = 18,000 , Feed = 325 ipm , Plunge = 250 to 275 ipm. the only adantage for the 1/2" cutter would be that it wouldnt leave "meat" left in middle of the 1' circle you are attempting to cut. therefore no worries about the tiny middle piece causing an issue with getting loose and in the way. hope this helps????

dont quote me on this, but you might want to check in under settings, control definition manager,linear settngs, and make sure they are all set to "DO NOT BREAK LINEAR MOTION". Ive had this issue before and its always when im tabbing and running a new version of MasterCam that I have forgotten to change in the preferences right away. just my 2 cents, hope it helps.

I dont know what you use to hold your material down, but we use vacuum here and have great suction that will hold that little centre piece down after the full cut. if you use vacuum pumps, maybe solution is more cfu? just a thought