How am I screwing up G41/G42 Compensation?

[Swami]

I am still trying to just get this going in Cutviewer, let alone my actual cutting.

Here is my simple test program. I want to remove .25mm material from the edge of this material using cutter compensation.

Compensation appears to be ignored, and the first cut winds up being .25mm + the radius of the tool.

Any help greatly appreciated!
Thanks,
Swami

----------
(TOOL/MILL,4,0,25,0)
(STOCK/BLOCK,200,25.5,6.35,0,0,0)
(FROM/-5,5,10)

(Setup)
G90 G21
G00 G90 X-5 Y5

(SmallPocket Entry Move)
G00 G42 Y0 X0 Z-1 D4

(What is supposed to be a .25mm cut)
G01 Y.25 F200
X46

M30
%

[ESjaavik]

And that is to be expected isn't it?
G-code is new to me too, and tool comp is one of the more difficult things.
But you have to start the tool comp on a lead in move, that will follow a different path for differing tool sizes, so it should be done through material that does not belong to your part. It might be explained as a move starting with the center of the tool at the programmed line, and ending up with the cutter to the right (G42) of the end of your line by half a cutter diameter. And the cutter edge will have passed the tangent to the endpoint of the line by half a cutter diameter. The path should continue straight ahead or to the left, or your program will *****. This is because you told it to gauge into your part. So much I believe I got right. but the not so easy part is how to do this. Especially approaching the inside of a circular pocket.

Anyone care to explain this in an easily understood way?
Or to correct me if I'm wrong in what I wrote?

[Al_The_Man]

The first move in a G41 G42 should be an initial move to pick up the Offset and should not be part of the machining process, the move should be greater that the radius of the tool. The plane (X,Y) G17 is usually implied, and does not have to be stated. Older controls required a I or J value to indicate the axis offset direction of the first cut. It look like in your case the offset is not being picked up, do you have the right offset in the D4 value? What is the controller?
Al

[Swami]

Im just trying to get CutViewer to show this for now, but I use Mach2.
I originally thought D4 would be diameter of 4, but now I think it might mean "refer to tool 4" However, I have switched to D1 (with a defined 4mm tool), but still have the same problem.

Mach2 finds some wild orbits to try to get in there, but then there are plenty of errors about concave corners.

If someone could correct the script above, I think I could figure it out.

Thanks!
Swami

[Al_The_Man]

Yes the D is usually a Diameter register where the diameter value is stored.
So your first move should be at least 2mm which it look like it is, did you try doing the Z move on a separate line before or after? see if that makes a difference.
Al

[Swami]

Yes I did try putting the Zmove on the next line. No better...

[ger21]

In Mach2, all inside corners less than 90° need to have a radius if using G41-G42. The radius should be a little bigger than the tools radius.

Try something like this

G00 G90 X-5 Y5
G00 X-1 Y1
G42
G01 Y0 X0 Z-1 D4 (comp should occur during this move)
G01 Y.25 F200
G01 X46
G40
G00 xxxx (Exit move to remove comp)

Not sure how the D works in Mach2, though.

[High Seas]

I've been trying to figure this out too, so I tried the following:
I used the wizzard in MACH2 to work this out - - maybe this will help - I hope so. There is a difference in left/right compensation tooMight check that as a possible problem. The file is supposed to cut a circle with diameter of 10 inches, with a 0.25 tool with compensation. Haven't tried it other that a few sims in MACH2.


G0 G49 G40 G17 G80 G50 G90
M6 T0(TOOL DIA. 0.25)
G20 (Inch)
M04 S0
G64 (Constant Velocity Mode)
G00 G43 H0 Z0.1 (G43 apply tool offset LENGTH)
X4.7125 Y0.14375 (a location that includes the offset ~ I guess)
G01 G42 P0.125 X4.85625 F15 (G42 gioves the radius compensation for the 0.25 tool)
G01 Z-0.9000 F30
G02 X5 Y0 R0.14375 F15
G02 X-5 Y0 R5
X5 Y0 R5
G02 X4.85625 Y-0.14375 R0.14375
G40 (turns off compensation)
G00 Z0.1
M5 M9
M30
(end of file )
Cheers - Jim

[Swami]

Originally Posted by ger21 In Mach2, all inside corners less than 90° need to have a radius if using G41-G42. The radius should be a little bigger than the tools radius. Try something like this

The code ran, but the DRO showed that a cut happened at Y=0.25. Shouldn't the DRO show the compensated value of Y?

Thanks,
Swami

[Swami]

I am still very shaky on this, but I got my one example to work like this:

G90 G17 G21
(Start on the "left side" of the path)
G00 G90 X-5 Y5
(Entry Move)
G00 G42 Y.25 X0 D1
X46
M30

Now I just have to see if I can figure out how to get started on my REAL part, lol.
Thanks!
Swami

[Swami]

Man this is nuts. I swear that code just worked, although now it is not working

[ger21]

Originally Posted by Swami The code ran, but the DRO showed that a cut happened at Y=0.25. Shouldn't the DRO show the compensated value of Y? Thanks, Swami

It probably should, but probably doesn't ( I haven't actually used Mach2, but I do read all the Yahoo messages)