What you have there is , it will go to X1Y1 then bore a hole striaght down to -.5 then try to cut the circle (;-) You might want to add in 2 more params.
Param1 sets #550 with Setvar(550,Param1)
#551 gets set with Code"#551=[#550/2]"
From there everything is in place to cut the circle. I am using it and it works great.