Issue #7913 - Path not going to the bottom of a pocket

[acp693]

Hi, I have a pocket that's 1,2mm wide and I'm trying to create a path with a 1mm tool, a few path lines are drawn, but they don't reach to the bottom of the pocket.

Has anyone got an idea how to fix this?

Thank you.

Tested with the latest development version and the current stable version.

Attached file was created with the latest development version.

Code: Select all

OS: Windows 10 Version 2009
Word size of FreeCAD: 64-bit
Version: 0.21.31109 (Git)
Build type: Release
Branch: master
Hash: c23ee7ad88433a0f00e84afae0a62fe738be0c09
Python 3.10.8, Qt 5.15.4, Coin 4.0.0, Vtk 9.1.0, OCC 7.6.3
Locale: German/Germany (de_DE)
Installed mods: 
  * BIM 2021.12.0
  * CurvedShapes 1.0.4
  * Curves 0.5.3
  * FeedsAndSpeeds 0.4.0
  * Marz 0.0.26-alpha
  * Silk 1.0.0

[chrisb]

where does this Extrude come from? If I replace it with something simpler, while leaving everything else as is, the effect vanishes.

[acp693]

The extrude comes from a much more complex model, the rest of which is working. I made the example with that small piece of extrude because it was difficult to get the file under 1mb rather than uploading the whole model.

I’ve noticed the same, if I create a simpler pocket it works. But the pocket made from the extrude I have is wider than the tool, ( tool = 1mm, pocket is at least 1.2mm wide) the walls of the pocket are completely vertical, why does the path stop half way down the pocket? I’m ready to mill my model except for this step.

[acp693]

I've noticed that there's an error message, I didn't see it at first.

09:25:18 <Path.Area> Area.cpp(1576): Discard empty section
09:25:18 <Path.Area> Area.cpp(1576): Discard empty section

What does this mean?

[chrisb]

I have no idea where it comes from, but as a workaround you can adapt the depth so that it fits.

[acp693]

Thanks for the suggestion.

If I set the final depth to 6,99mm, the path doesn't reach the bottom of the pocket. If I set it to 6,98mm it goes through the bottom.

[chrisb]

Correcting the depth didn't work as expected - I had tested yesterday, but not with the exact values, and it is the decimals which somehow get rounded.

So here is a new workaround, where you have to add another pocket operation with modified final depth (6.73mm), FinishDepth (1mm), big Stepdown (3mm) to skip what was milled before.

To help the developers, you should reduce the issue to the bare minimum, i.e. simplify the extrude as far as possible so that the issue still occurs, and create a ticket on Github.

For some unknown reason my file has 2.4MB, even with only one pocket.

[chrisb]

We crossposted. If I set your value of 6.98, the mill goes down to 7.5 instead of 7.73.

[acp693]

We crossposted. If I set your value of 6.98, the mill goes down to 7.5 instead of 7.73.

yes, that's what happens with me too. It goes through the bottom of the pocket.

This workaround seems to hit exactly the bottom of the pocket:
Set start depth to a multiple of my step down(0.5mm at the moment) i.e. 10.23mm. This stops 1mm short of the bottom of the pocket. Change final depth to 6.73mm instead of 7.73mm allows it to reach the bottom of the pocket exactly

The model is as simple as I can make it and still demonstrate the problem. even with maximum compression it was still over 1Mb, I've zipped the file and it now allows me to upload it. I don't know how to submit a bug report.

Thanks for all your help Chris.

[chrisb]

Can you upload the sketch creating the B-splines? If I create one from the extrude, it has 475 DOF for one side. It has no controlpoints, but a degree of 15. Does it really have to be that complicated?