Messages

11

G-Code, CAD, and CAM discussions / Re: G-code oddities..

« on: November 01, 2010, 05:23:12 AM »

Spirals are an undocumented feature. I don't have the info handy, but the endpoint of a circle is allowed to deviate by up to 1/2".

I think what you're seeing is that G41/G42 will not work correctly with a spiral move.

Ok, thanks that [confirmation that it was undocumented feature] was the kind of info I was looking for.

br Kusti

12

G-Code, CAD, and CAM discussions / Re: G-code oddities..

« on: October 31, 2010, 12:54:43 PM »

Thanks again for looking at this.

We seem to be getting nowhere fast ;-) but if you look at my picture:

http://www.sparetimelabs.com/gplot.png

the white line is the compensated toolpath.

Starting from the origin at 0,0 the first two lines:

G1 X0 Y0
X0 Y2 G42 P0.2

produce the slightly slanted lead in move, correctly.

Then the next G-code line is (thats absolute IJ mode):

X1 G2 I2 J2

Now in my view this should produce an error message because
there is no arc that can be drawn from 0,2 to 1,2 with arc center at 2,2.

But it produced the white horizontal segment in the compensated toolpath,
or a sprial (the purple line) for the uncompensated path. Both seem to be wrong,
in that Mach3 manual mentions nothing about spirals and OTOH if spirals are
valid resulst for G2/G3 moves, why is the compensated spiral suddenly a
horizontal move?

You also wrote:

"You also may want to study up on the structure of the block coding.
Certain things come before others or unexpected results can occurs."

According to Mach3 manual:

"The first group (the words) may be reordered in any way without changing the meaning of the line."

"If the second group (the parameter settings) is reordered, there will be no change in the meaning
of the line unless the same parameter is set more than once. "

So I do not see how that would apply here.

br Kusti

13

G-Code, CAD, and CAM discussions / Re: G-code oddities..

« on: October 29, 2010, 10:07:37 AM »

Thanks BR549/TP,

for answering, but my question was slightly different.

I was interested why the G-code I presented resulted in a spiral when according to the manual it should have resulted in an error (or so I gathered)?

The other oddity was that while the uncompensated path looks like a spiral the compensated path looks totally different, how come?

I know about lead in and lead out, in fact I was just investigating those when I came up with this issue and question.

My sample was just an artificial code fragment to illustrate my point which can come up for example if your lead in/out is not a straight segment but an arc, or if the tool (raidus/compensation) changes between two arcs. I'm curious how that is handled by Mach3 and was hoping for some insight into this.

br Kusti

14

G-Code, CAD, and CAM discussions / G-code oddities..

« on: October 28, 2010, 01:18:46 PM »

Hi,

I'm using the Mach3 to study G-code and to test a corner case I wrote:

G1 X0 Y0
X0 Y2 G42 P0.2
X1 G2 I2 J2
Y4 G1

This produced something like this:
(screen cap from Mach3)

http://www.sparetimelabs.com/gplot.png


Two things strike me as odd.

1) According to Mach3 manual 1.84 when using G2 with arc center format:

"It is an error if when the arc is projected on the selected plane, the distance from the current point to the center differs from the distance from the end point to the center by more than 0.0002 inch (if inches are being used) or 0.002 millimetre (if millimetres are being used)."

Now clearly I've violated this in my code but I get no error message, how come?

The path is show as a spiral (which kind of makes sense), is that normal?

How do other software handle this?

The compensated tool path does not follow the spiral at all, rather
produces something strange, is that correct?

Can anyone shed any light on this?

All comments welcome..

br Kusti