Modified FANUC post-processor for 4th axis cnc outputting rotation b-code that is offset from the rest of the toolpath when origin is placed at the top of the stock

[connor.workman]

Hi,

I'm trying to get a modified FANUC post-processor working with my machine's 4th axis rotary.

Placing the origin at the center of the rotation works fine, but placing the origin anywhere else causes the rotation to occur around the axis of that work origin, and the rest of the toolpath to generate normally.

I've prepared an example to illustrate with a simple slot of a cylinder:

Here the origin is set to the center of the object, with the corresponding gcode attached. Visualized, it looks like this:

Now for setting the origin where it actually needs to be, at the top of the object:

The corresponding gcode is attached. Visualized, it looks like this:

When run, the bit hovers over the piece except for at the very ends, where it plunges deeply into the material.

I would appreciate any help on this.

[a.laasW8M6T]

As you have found, you need to place the WCS at the center of rotation of your rotary.

Why does the WCS NEED to be at the top of the part?

You can still touch off the part on the top, you just have to set it to 0.5 x the diameter of the part, this will correctly locate your WCS on the rotary centerline

[connor.workman]

This is an interesting limitation that I have not found in any documentation.

Obviously adjusting the WCS separately from the center of the rotation is ideal, but if it's not possible it's just another reason to look for other solutions outside of fusion360.

[a.laasW8M6T]

Its not a software limitation, its a limitation of the machine controller.

If the control doesn't support tilted work plane(G68.2) and/or TCP(G43.4) then you must program from center of rotation, this is extremely common on 4 axis machines as most do not have these features enabled.

I think you will find all other cam software will have the same issues

[programming2C78B]

Correct, we also have multiple machines here with 4th. All require Center Of Rotation. It should almost never be changed at the machine, which for us is 5" from the table.