[mfg-smartcam] a little story about "i"'s and "J"'s

[Chris Peters]

Hi all, has anyone had trouble with interpolating bores with cutter comp?  The .pm4 geometry is completely round, but once you run it on the machine, you end up with an oval? our immediate action was to change the coded output from "R" values to "I" and "j" outputs, which seem to lock down the quadrant boundaries for Fanuc and gave us a nice round bore.   does this sound familiar to anyone?  you see the problem is there are other tapes on the floor that use "R" in cutter comp and they function perfectly well!   we tested different lead-ins and consistently, the i's and j's gave us a round hole, and the "r" gave us an oval.  it was a 5/16 em, cutting a .793 dia bore with circular lead-in and lead-out. the y dia is .010 larger than the x dia.   I'm pretty sure it's a Fanuc-ism that causes the ovality (a "best-fit" type scenario), but the question is, is it because we are crossing quad boundaries with an "R"? is it because our tool dia is less than half the interpolated dia? are there any mathematical braniacs who can decipher this geometric conundrum for us simple machine-heads?   go figure