Adaptive toolpath part incursion bug in 0.20.2

[areseeuu]

I have a gantry router (a PrintNC) that I occasionally cut steel with. Since a PrintNC uses a high speed spindle and is nowhere near as rigid as a VMC mill, slotting in steel is something I try very hard to avoid. For today's part, I had a need to profile part of a shape, so I figured I would model a mock part that would result in the desired trochoidal milling path - but when I generated the path, it cuts in an unexpected place that would screw up the part. I reduced the mock part to the minimum complexity needed to recreate the issue - here's what it is:

freecad-adaptive-path-part-incursion.png (26.79 KiB) Viewed 426 times

freecad-adaptive-path-part-incursion-closeup.png (46.3 KiB) Viewed 426 times

The part is two sketches: The first one is a 50mmx50mm square centered on the origin and padded to 10mm height. The detail of the second sketch is shown here:

freecad-adaptive-path-part-incursion-pocket-sketch.png (48.39 KiB) Viewed 426 times

Then, create the Job object, leave everything as the default, then select the face of the pocket and click Adaptive. The screenshots above were without the finishing profile option checked, but it shows the same deviation:

freecad-adaptive-path-part-incursion-operation-options.png (109.86 KiB) Viewed 426 times

Playing around with this, I've noticed that if I decrease the upper angle constraint to 5.46 degrees or less, it goes away. 5.47 degrees shows the bug.

[chrisb]

Hi and welcome to the forum!

Please add the file - and your full FreeCAD infos.

[areseeuu]

Here's the file:

freecad-adaptive-path-part-incursion.fcstd

(56.25 KiB) Downloaded 7 times

Here's the FreeCAD info:

Code: Select all

OS: Debian GNU/Linux bookworm/sid (GNOME/gnome)
Word size of FreeCAD: 64-bit
Version: 0.20.2.
Build type: Release
Python 3.11.1, Qt 5.15.8, Coin 4.0.0, Vtk 9.1.0, OCC 7.6.3
Locale: English/United States (en_US)

[GeneFC]

This exact problem came up on the forum several months ago. (I looked, but could not find the previous discussion.)

It seems to be related to very specific parameter settings causing some sort of math failure.

I do not know any fix at this time other than watching for it and then tweaking parameters to get rid of the bad moves.

Someone else may have more information.

Gene

[Russ4262]

Here's the file: ...

The solution is to increase the "Stock to Leave" value to greater than zero. I use 0.001 mm because that is within my tolerance, but you might use 0.5 mm, and then add a Profile op afterward to remove that material.

Russell

Code: Select all

OS: Windows 10 Version 2009
Word size of FreeCAD: 64-bit
Version: 0.21.0.32198 (Git)
Build type: Release
Branch: master
Hash: f51b2156f35399cab38eef1e957a59ad5a11de66
Python 3.8.16, Qt 5.15.6, Coin 4.0.0, Vtk 9.1.0, OCC 7.6.3
Locale: English/United States (en_US)
Installed mods: 
  * FC_SU
  * freecad.gears 1.0.0
  * PathExp
  * Z_MacroStartup

[areseeuu]

This is working! Thank you Russell!

[chrisb]

You can decrease the diameter of the tool by the same amount in case 1µ is too much .

[MRx]

So easy apply my fix and the issue is gone

I am not going to spend a single second anymore on that particular code part since I'm working on other things.
I'm using this patch since it was released and never looked back.
Back then I had tons of issues with FreeCAD because I worked on a project which seemed to be a bit difficult for FreeCAD and which has shown me several limitations...
After I released this patch I was already working on other things.
If someone doesn't like what the patch looks like feel free to change it... but the FreeCAD way seems whatever waste developers time and keep going with the bug - OK

The reason why this bug happens is in clipper, the fix addresses that values which are directly nearby will be filtered. eg. 1,3,6,7,8 - 7 will be filtered out since clipper cannot handle the direct next number when shrinking or growing an outline.

https://github.com/FreeCAD/FreeCAD/pull/5276

[chrisb]

I have added a section "Known issues" to the wiki of Path Adaptive

[Russ4262]

I have added a section "Known issues" to the wiki of Path Adaptive

I recommend that the suggested solution not be to adjust the diameter of a tool, but use a reasonable value for "Stock to Leave" and then follow the Adaptive op with a Profile op to finish the side walls. I think this is more in line with how a machinist might mill the part, using the Adaptive op for clearing, then a Profile and possible Pocket/Surface op for the final finish.

Just my recommendation. I would not want someone to adjust the tool size, then forget about the adjustment and use that tool on another operation, which would then introduce an error in that machining process.

Thanks for all your help, sir. Your support for FreeCAD users is fantastic!

Russell