[Paddle_guy]

Hi all,
New to the forum here. I've been writing programs on MasterCam and have noticed the I,J, and K codes in there. I've tried playing with them a bit, and understand the premise of the center of the circle theory. What I don't understand is why there was only one instance of the I and J codes at the beginning of the program. Does this mean that these I and J values work for the whole program? What happens to my toolpath if I alter them?

[mmoe]

I and J codes will only happen where there is an arc. Depending on the source geometry, sometime the "arcs" are actually segmented lines, in which case there would be no I/J output even though it looks like the machine is going around an arc. Otherwise, you are asking if I/J outputs are modal, and they are generally not. Most controllers are set up with "incremental" I/J values whether the normal XYZ values are absolute or incremental, so the location of the center of the arc (I/J) is always subject to the current position of the tool before the next move is made. If you move from one point to another around arc center I/J, and the I/J values are incremental and not absolute (as is most common), the same arc center is now a different value if you wanted to continue around that center point unless you had done a full 360 degree turn around it. In incremental I/J, the I is the X value relative to the current X position and the J is the Y value relative to the current Y position. I've attached a sketch of two moves around the same center point, but you'll see that the code for the I and J are different for each move even though it's the same point being reference to pivot around.

If you aren't getting I/J codes output and you have curves in your drawing, either the curves are actually small line segments approximating the curve, or you need to enable arc output in the CAM system. In the case of the latter, the CAM system may break arcs/curves down into line segments during the toolpath generation since some machines require lines instead of arcs. I'm not a Mastercam user, but I'm guessing that there is a setting that is either system wide or available when creating each toolpath feature. Check your geometry first to verify there are curves. It sounds like the first move may be a circular lead in, which seems to me to point to the geometry itself being line segments. You can post a DXF example if you like.