[solved] different meassures between LinuxCNC and QCAD

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cki61
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Posts: 18
Joined: Fri Jan 19, 2018 5:43 pm

[solved] different meassures between LinuxCNC and QCAD

Post by cki61 » Sat Apr 14, 2018 4:04 pm

Sorry, I momentarily can't find my error. I create a circle in QCAD (its a polyline from another program) of diameter 27mm, please see appended image 01. Has to became o hole of that diameter size. I cut it inside with a tool of radius 1mm/diameter 2mm. To get a hole of 27mm I have to cut a circle of 27-2*1=25mm.
the generated gcode imported to LinuxCNC can be seen at image 02. So the cutter generates a hole of diameter=26mm.
Where has the 1mm been lost?
I'm sorry, I couldn't. Maybe you or anybody else is more successfull.
The circle dxf and ngc files are appended.
Postprocessor is LinuxCNC[mm], the new one not yet in release!

Every help is appreciated.

Best Regards,
Christof
Attachments
kreis_OK.dxf
DXF
(188.62 KiB) Downloaded 7 times
kreis_OK.ngc
GCode
(1.68 KiB) Downloaded 9 times
Screenshot_Kreis_27mm_LinuxCNC.png
Image 02: Circle 27mm in LinuxCNC (should be 25mm instead of 24mm)
Screenshot_Kreis_27mm_LinuxCNC.png (57.27 KiB) Viewed 393 times
Screenshot_Kreis_27mm_QCAD.png
Image 01: Circle 27mm created with QCAD
Screenshot_Kreis_27mm_QCAD.png (21.32 KiB) Viewed 393 times

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andrew
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Joined: Fri Mar 30, 2007 6:07 am

Re: different meassures between LinuxCNC and QCAD

Post by andrew » Sat Apr 14, 2018 6:41 pm

The LinuxCNC postprocessor uses tool radius compensation (G41/G42), so the programmed contour is the final contour, not the offset path of the tool center.

You can see from the G-Code that the diameter of the approximated circle is indeed 27 units as expected when using G41/G42 for compensation:

Largest X value:
N430 X29.5 Y15

Smallest X value:
N790 X2.5 Y15

29.5-2.5 = 27

The output of LinuxCNC would indicate that the tool radius has not been set to 1, but to 1.5. Perhaps coming from a tool table configuration file or similar.

cki61
Junior Member
Posts: 18
Joined: Fri Jan 19, 2018 5:43 pm

Re: different meassures between LinuxCNC and QCAD

Post by cki61 » Wed Apr 18, 2018 8:40 pm

Hi Andrew,

you where completly right, beginners error. I forgot to adjust/synchronize the QCAD/LinuxCNC toolsets.
Mea Culpa.

Best regards,

Christof

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