You could use Create > Spiral to create a spline; make one CW and another CCW with the same parameters and center point and it will be a mirror. Use the spline as your tool path. It won't do a full arc on the perimeter, though. You would have to create a circle on the perimeter and then be careful with your tool path selection. That's a quick and easy way to do it.

I had a weird bug that froze my computer on opening the program, and opening a file... it started after I had selected that I would like to provide automatic feedback in the customer feedback program. It took me a long time to figure out just what the h was going on. I had to sit and think about everything I had done that might have screwed up the machine, and work my way back. Turns out it was that... maybe it's because I work over a network, but just selecting that box royally effed things up. So you might want to give that a try and see if it was activated. It's under Help>Customer Feedback Program

I don't know what control you use; most of my experience is with Fanuc and Okuma. They work pretty similiar minus different G and M codes, and variable calls. What I would do is make a macro subprogram that can reside in your machine, and give it a number that isn't likely to be changed (in Fanuc controls you can lock out 8000 and 9000 series programs. I make my macros there and lock them). Using system variables you can pull all your numbers and have the control adjust them. So lets say for example I make my macro on a Fanuc, and name it O9009. In MDI I would type in a simple macro call: G65 P9009 X1 Y0 T1 This calls up the macro. The X1. or Y1. would be where you tell it what direction you want it to move: in X or Y. Using a "1" would mean that's the direcion you want, a "0" means you don't want it. T obviously calls the tool you want. The macro subprogram would look like this: O9009(BLEND MACRO) #500=[11000+#20] //this specifies which length offset to change #501=0 //this is a counter G90 //absolute mode G43 H#20 Z.010 //this calls your length and moves .010 above the surface N9999 //address IF[#24 EQ 0] GOTO 8888 //X decision N9000 //address M01 //optional stop G91 G1 X.1 Z-.008 F3. //ramp onto part X.5 //move forward to make mark X.1 Z.008 //ramp off of part X-.7 //return to start position Z-.0001 //move down small increment #501=#501-.0001 //add increment to counter GOTO 1111 //GOTO the decision process N8888 //address IF[#23 EQ 0] GOTO 7777 //Y decider N8000 //same as above but in Y M01 G91 G1 Y.1 Z-.008 F3. Y.5 Y.1 Z.008 Y-.7 Z-.0001 #501=#501-.0001 GOTO 1111 N1111 //address IF[#500 EQ 11001] THEN#11001=#11001+#501 //here is where it decides what tool offset you are using and adds the increment to your offset ... //not going to type them all out IF[#500 EQ 11030] THEN#11030=#11030+#501 //your last number would correspond to your highest tool GOTO N9999 //restart the loop N7777 //address #3000=1(YOU MUST SPECIFY X OR Y) //will alarm out if you didn't set X or Y to 1. M99 //end of program You can let the macro run in a loop until you see it touch. Once you do, you can flip on optional stop. The macro will make its additions, then stop, at which point you can reset and go home, and your tool will have the right length. This assumes that you already had your tool in a safe position to do this macro, and that you trust it enough to go down to within .010" This is just a rough macro, it's up to you to finesse it the way you like. If you don't have a Fanuc I leave it up to you to find and make the necessary changes. Even if you do have a Fanuc, you'll still have to make changes depending on what model control you have.

Super easy macro to make. Do you want the tool to move continuously and you stop it when it makes contact and then plug in the deviation to your offset; or do you want it to make a step, plug in an offset, make another step, etc.?