# Thread: 4th axis programming challenge...Help!

1. ## 4th axis programming challenge...Help!

I have a part to machine that is a cam. It seems fairly simple, but a limitation with the Fadal 88HS control is complicating matters for me.

Basically the cam is a 6" diameter round part, with a continuous cam slot milled around the circumference. Typically, I would position the tool at the starting point in X, with Y on the part centerline. Feed down into the part in Z, then use a G1 X.... A.... command to feed the tool in X, as the rotary rotates. At the 180 degree rotation point, the toolpath for X is reversed, bringing the tool back to the original starting point when the rotary finishes 1 rotation (360 degrees).

Simple enough.

But here's the kicker: the print calls for the tool to make a partial arc in the XY plane, as the rotary rotates. The toolpath calls for the tool to make the partial arc clockwise during the first 180 degrees of rotation, then counterclockwise during the 2nd 180 rotation, with the tool ending back where it started in X,Y, and A.

But alas, according to the Fadal manuals, you cannot program an A-axis rotation on the same line as a G2 or G3!! An A command can only occur on a G0 or G1 line.

I am stumped. Any ideas on this one??

Thanks,

Greg

2. ## I believe if I understand you correctly...

...you will have to segment the arc moves with very small G1 point to point moves along the XY and A axis. That's what we did it in the old days.
I use to do it on the an old 2 and a half CAD CAM system... it does get a little tricky on just which of the axis are moving and to make sure your are staying within your band width of tolerance.
If you have a newer CAD system it much easier to segment the the A arc and the XY on that rotary surface.

Steve

3. Draw the path on the flat (X=X? and Y= 18.85 Circumference) with the arcs.
Cam the path using segments.
Change all the Y dims (multiply by 19.098) to A
IMHO

4. I posted this on your thread on PM. It looks like G17 (or perhaps G15) are the keys to what you want. How to use them is described in Section 12 of the Fadal User Manual (Rotary Axis chapter).

5. Post the straight line code and the radius of the arcs and I will see if I can generate some code.

6. Check your User's Manual and read up on Cam Wrapping (Flat cam) programming.

Neal