G2 arc problems

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14 Nov 2016 03:34 #82757 by chadrat6458
G2 arc problems was created by chadrat6458
Created a 5 sided polygon with Cam Bam. I went to cut it out with LinuxCnc. It displays a huge circl. Like 1000 inches. Tried to produce the g code again in Cam Bam. Same results. Looks fine in camtronics simulation software. What is going on?

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File Name: shahan-Part3-25.ngc
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14 Nov 2016 03:59 #82760 by tommylight
Replied by tommylight on topic G2 arc problems
There is something wrong with the I and J values, i have no idea how they got to be so out of order. X and Y values are all good. Check the post processor.

G1 X4.00139 Y-3.49672 <===good
G1 X4.18204 Y-2.9405
G2 X4.36431 Y-2.37939 I7013.92718 J-2278.09925 <===no good
G2 X4.53866 Y-1.84284 I5832.15523 J-1894.78228
G2 X4.68664 Y-1.38755 I5420.26082 J-1761.51289

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14 Nov 2016 11:55 #82766 by andypugh
Replied by andypugh on topic G2 arc problems
It is possible that the problem is the G91.1 / G90.1 setting (absolute or relative arc centres) but, really, the numbers look crazy even then.

linuxcnc.org/docs/2.7/html/gcode/g-code.html#gcode:g90.1-g91.1

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14 Nov 2016 14:49 #82779 by Todd Zuercher
Replied by Todd Zuercher on topic G2 arc problems
I would also recommend twiddling with your post processor's settings. If I look at the code with the backplot program I usually use I don't see any problems, but when I open it in a Linuxcnc simulation I see 4 bad G3 arcs (line 61 and 94 and again when they are repeated later). If I change those 4 lines to G1 Lines the code runs fine. All the problem arcs I see are very large radius, and I don't think changing them to lines changes the shape of the intended part appreciably. However I am not seeing what the real problem is with those arcs (why they are being turned into circles).

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