[solved] different meassures between LinuxCNC and QCAD

[cki61]

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

[andrew]

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]

Hi Andrew,

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

Best regards,

Christof