Problems with scetch mappings and external references

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lboc
Posts: 2
Joined: Wed Apr 17, 2019 8:53 pm

Problems with scetch mappings and external references

Postby lboc » Sat Apr 27, 2019 10:53 am

First of all I am sorry if I am reposting an old problem here but I could not find a post that discuss a solution to this problem.

When using sketches, building pads and pockets and then going back to edit the first sketch, things can get really bad and everything gets re-mapped to other faces and external references can break.
I am thinking the root cause of this is naming of edges and planes. For instance if you edit a sketch, all edges are named from Edge1..n. If you delete Edge1 the earlier Edge2 now becomes Edge1. This will also cause later pads and pockets to have their faces renamed.

What if instead edge names are never reused AND pockets and pads uses its base edge names as foundation for naming the faces. For pads, bottom and top faces could have fixed names. Then modifying sketches would not break mappings to faces in later stages.

Just a thought.
jmaustpc
Posts: 9528
Joined: Tue Jul 26, 2011 6:28 am
Location: Australia

Re: Problems with scetch mappings and external references

Postby jmaustpc » Sat Apr 27, 2019 11:37 am

Hi and welcome here.
Search "topological naming" and you will find numerous posts, its a limitation that can be worked around in PartDesign in FreeCAD 0.18.

The long term fix is complex, there has been some work on this by a developer, but not in master.
chrisb
Posts: 16867
Joined: Tue Mar 17, 2015 9:14 am

Re: Problems with scetch mappings and external references

Postby chrisb » Sat Apr 27, 2019 12:54 pm

You can avoid most of the problems by thoroughly designing your model according to this page, especially the paragraph about creating stable models is important.
lboc
Posts: 2
Joined: Wed Apr 17, 2019 8:53 pm

Re: Problems with scetch mappings and external references

Postby lboc » Tue Apr 30, 2019 10:02 am

jmaustpc wrote:
Sat Apr 27, 2019 11:37 am
Hi and welcome here.
Search "topological naming" and you will find numerous posts, its a limitation that can be worked around in PartDesign in FreeCAD 0.18.

The long term fix is complex, there has been some work on this by a developer, but not in master.
Thanks, do you have any references to the above work? I do code python, perhaps I can help...

And thanks for the link above.
vocx
Posts: 720
Joined: Thu Oct 18, 2018 9:18 pm

Re: Problems with scetch mappings and external references

Postby vocx » Sun May 05, 2019 6:54 pm

lboc wrote:
Tue Apr 30, 2019 10:02 am
Thanks, do you have any references to the above work? I do code python, perhaps I can help...

And thanks for the link above.
See topological naming problem for further explanation on this issue.

The core FreeCAD routines are coded in C++. They are hard to understand, that's why only a few people know more or less how to approach the problem. You don't only need to know C++ but also be very familiar with the core components of the "documentObject" system of FreeCAD.

Realthunder, a user of FreeCAD has been working on this issue for a long time. He basically forked FreeCAD and has been adding new code to fix the topological problems but also provide tools to do better Assembly. In the forum you'll read many notes about "realthunder's branch", and "LinkStage3", and "Assembly3"; all that is prototype code that is in development, and that possibly in the future will be merged into the core of FreeCAD. You can download and test his branch.

There is a ton of information to read: Assembly3 preview