Strange preview for circular arc (G2/G3)

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09 Mar 2026 20:56 #344070 by Hannes
Replied by Hannes on topic Strange preview for circular arc (G2/G3)
BTW2:
If you want do do helix milling, I created a macro. See

File Attachment:

File Name: boring.ngc
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It is called like that:

o<boring> call [-10.0] [4.0] [10.0] [1.0] [1000.0] [3000.0]

The center of the helix starts at [0 0 0]. To shift it, I was using a second coordinate system like that:
G54
G0 X0 Y0 Z0 ;Or what ever the starting position in G54 should be
G10 L20 P2 X10 Y20 Z5  ;Offset of hole relative to actual location ->G55
G55 ;Activate G55

o<boring> call [-10.0] [4.0] [10.0] [1.0] [1000.0] [3000.0]

G54 ;Activate G54 again for future moves
 

Probably there are better ways doing this, I'm also just starting writing G-Code. For example you could pass the starting location as a parameter or use variables to create the new coordinate system.
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10 Mar 2026 09:45 #344084 by Finngineering
Replied by Finngineering on topic Strange preview for circular arc (G2/G3)
Thank you Hannes. I made a bug report as you suggested:
github.com/LinuxCNC/linuxcnc/issues/3855

This was a real use case and a toolpath I intended to use immediately. I was trying for an hour or so, wondering how I can mess up or misunderstand such a simple command. I then gave up and made this thread some time later. I would think I had the command right from the start, just that incorrect preview threw me off. And I did have a fair bit of confidence in the preview, because I had previously used several somewhat complicated CAM generated programs, and the preview always looked fine. Well, at least I know the reason now.

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