Actual toolpath doesn't match displayed toolpath or simulation

[etfrench]

This rather simple 2d contour tool path for a T-Nut did not machine the full path.  In the screenshot there are three toolpaths combined where each toolpath was just created from a line:

Here are the actual toolpaths:

Work around was to change the part slightly so there as a continuous contour for the ledge. Here's a video of the bad toolpath and the work around:

Gcode file is attached.

[Matthew-R]

@etfrench Thanks for posting your issue to the Fusion 360 forum. Would you be able to export and attach the Fusion 360 file to the forum thread? It would be very useful in diagnosing what the cause of the issue that you are experiencing is. Thanks again and looking forward to your reply.

[etfrench]

I'd rather not post the file publicly as it is part of a larger assembly.  I can either send it in an email or add you to the project.

[porsbym]

Looking at the G-code you attached, it does appear to match your screenshot from Fusion which suggests to me that the problem lies with using an inappropriate configuration of post processor or NC control.

/Mark

[etfrench]

The post processor is the same for the abnormal toolpaths and for the full contour toolpaths. It's the generic LinuxCNC(EMC2) post processor.

I created a new gcode file with the same toolpaths.  It is identical to the first failed toolpath file (except for the name change).  Running it in the air shows the same problem. (The arc toolpath is leftover from the previous job).

Toolpath settings:

[etfrench]

Removing the ramp eliminated the problem as did changing it to 10 degrees. When the ramp was changed to 2 degrees the problem increased.  The problem also repros in a file with a single sketch line.

[porsbym · Accepted solution]

I'm not familar with LinuxCNC, but looking at your screenshots it seems like there is some rounding going on.

Googling this a bit unearthed http://linuxcnc.org/docs/2.7/html/user/user-concepts.html#_trajectory_control which mentions that the planner will round corners in some modes. You can control this with G64, but I would think that there are also some defaults that can be set in your control.

For now, try manually adding G64P.001 at the start of the NC to tell the control to slow down in corners to stay within 0.001 of the actual path.

/Mark

[etfrench]

I normally have a slower ramp speed so the faster speed probably triggered the change in rounding.