Originally Posted by
cncsnw
If you are programming a Profile cycle, then the first move in the Profile needs to be an X-only line or rapid.
Since your arc is likely to start at the end of the part (or be further down the part), and you should always choose a Start Point for the Profile that is clear of the end of the part by at least twice the tool nose radius, this generally means that you need at least two moves in the Profile before the arc: one that just moves X down to your starting position, then one that moves Z in to the face of the part.
More commonly you need three lines, to ensure that the entire arc gets cut. This is because, if you are using tool nose radius compensation, your first move needs to overshoot the beginning of the arc by at least the nose radius.
For example, suppose you want to put a full radius on the end of a 2" bar, and your tool has a 0.032" nose radius.
Your profile Start Point needs to be at or above X2.0, and out to at least Z0.064. I would add a bit more, so that I don't run into trouble if I have to adjust my tool nose radius offset by a few thousandths. So try X2.1 Z0.1 for a starting point.
Your next move would be a Line or Rapid, staying at Z0.1, but moving X down past centerline, say to X-0.05.
The next move would be a Line, staying at that X, but bringing Z in to Z0.
Then a Line to X0 Z0 (the start of the arc)
Then an Arc: say EP&R, with an end point of X2 Z-1 and a Radius of 1.
The first three line moves make three sides of a box, approaching the start of the arc in a rather roundabout manner. This is necessary because you should be using cutter radius compensation (Comp Right in this case). If you picture a full circle, with the same radius as the tool nose, moving around the inside of that box, it fits with a little room to spare.
Suppose we had used X2 Z0 as the Profile Start; gone straight down to X0 Z0; then come up our arc. If you try to slide the cutter nose circle down the right side of the first line, then up the right side of the arc, it has to turn around long before it gets down to centerline. Much of your arc would be left uncut.