Canned cycles relative - G91 G81 doing two times

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29 Jul 2012 18:09 #22592 by juergen-home
I'm using linuxcnc2.5 with Axis. I read a lot but I'm still a very beginner.
When I tried to make relative caned cycles I do not really understand the result.
I make the same call 2 times a get 2 different results.

The gcode is:

G90 g80 G0 Z1 (coordinate home)
X0 Y0 f1000
g91 G98 G81 X5 Y0 Z-5 R3 L3
g91 G98 G81 X5 Y0 Z-5 R3 L3
G90 g80 G0 Z1
X0 Y0
M2 (program end)

With the first time of calling g81 I have a kind of triangle trajectory.
The second (and any other) call(s) the move is (from my sight) as it should be.

1. So what I'm doing wrong?
2. When I change G98 to G99 see no change of the trajectory

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30 Jul 2012 10:54 #22602 by Rick G
Not sure why you would have

g91 G98 G81 X5 Y0 Z-5 R3 L3
g91 G98 G81 X5 Y0 Z-5 R3 L3

together, but I would recomend a G80 after each canned cycle.

www.linuxcnc.org/docs/html/gcode/gcode.h...c_g80_cancel_modal_a

Rick G

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30 Jul 2012 11:32 #22603 by BigJohnT
It's a little difficult to understand but if you read the examples in the manual for G81 it should become clearer why your R value did not give you what you expected when using relative mode. The following code will give you what you expect. I assume but do not know as I don't see it specified in your example code that your using millimetres and not inches. It is a good idea to always put a preamble like shown in this G code tutorial .
G21 G17 G40 G49 G64 P0.005 G80 G90 G94
G0 Z1
X0 Y0
G91 G98 F1000
G81 X5 Y0 Z-5 R-1 L3
X5 Y0 L3
G80
M2

John

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30 Jul 2012 17:50 #22610 by juergen-home
True. Exactly that was I intend to do. I will read the manual once more.
Thanks
Juergen

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30 Jul 2012 17:56 #22611 by BigJohnT
BTW, the screen shot was a nice addition to your original post as it made it much easier to understand your problem exactly.

John

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