Re: Re: What does Tool Radius Compensation do ?

Andrew Werby wrote:

> If it does not have the G41 or G42 code anywhere in the program, then it
> does NOT assume the CNC is compensating for the tool.
>
> [It doesn't, so is there a way DeskProto could be compensating in software,
> independent of the milling program? Or is tool offset compensation
> irrelevant to my problem?]

OK, how do you make the three toolpaths? Do you rotate the part in the
CAD package, and then generate a new toolpath based on the rotated part?
That must be how you are doing it.

> I'm guessing you have the
> rotay table on its side, with the axis of rotation parallel to either X or Y.
>
> [Right- it's parallel to the x-axis.]

OK, that would be called an A axis.

> [Well, I'm still unclear as to how tool offsets function, but as it stands
> I wasn't using any, as far as I know. The question was- should I be? The
> next question: Is it possible?]

If your software doesn't support tool offsets, then it must be compensating
for the tool radius itself. Do you specify the tool size anywhere in the program?
I am pretty sure tool radius compensation is a 2-axis thing, although it could
be made to do 3 dimensional offsets, it gets a lot more complicated. When you
get into 3-D contouring, I think the only program that can adequately program
the toolpath without gouging is the one that has the entire surface description
available, so that has to be your CAD program, not the CNC control.

> [Actually, I wasn't changing the names of the axes, just rotating the part
> geometry along its own axis (parallel to the x axis) and instancing it as
> another part. DeskProto put in this facility with its recent upgrade to
> version 2.0, and it was my hope that the various instances would line up,
> since it seemed that the axis of rotation and the axis of construction
> would be congruent if I zeroed y and z to the tailstock center. It almost
> works...]

OK, now I see how you did this. But, it requires you to have the tool
aligned as the PROGRAMMER of DeskProto wants it. So, you need to
see whether there is any documentation on this in the DeskProto docs.

> But, maybe that brings us to the problem, being that if ONE axis
> is calibrated to the CENTER of the ball, ALL axes must be calibrated
> to the same point, the center. If you are applying a 1 mm offset for the
> cutter radius, when you turn the coordinate system, then the other axes
> must also be offset from the same point.

Yes, I think this might be the most logical way, so that the ref point
is the center of the ball. Are you getting too much material left, or is
it taking too much material away? Since you located at the tip of the ball,
I would guess it is leaving too much material, because the tool is one mm
higher than the program expects.

> [Except for the x axis, all axes are calibrated to the center line. It
> didn't seem to matter where the x axis started, except that x=0 should be
> toward the left, where the chuck is, in order for there to be room to cut
> the part. There doesn't seem to be any discontinuity between the instances
> in the x-dimension; the problem seems to be confined to the y-axis, or
> perhaps the z as well.]

Hmmm, yes, I think I see. The X is never affected by the rotation, so it
should be consistant. The Y is affected, because the rotation around the A
axis changes the Y coord of the completed surface.

Anyway, if the problem looks like a 1 mm gap of material between the faces,
then bringing the tool to touch the work, and setting the coords to Z=1mm
instead of Z=0mm as you are diong now, should fix it.

Jon