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IDProjectCategoryView StatusLast Update
0004154FreeCADBugpublic2021-02-06 06:49
Reporteraxos88 Assigned To 
Status newResolutionopen 
PlatformWindows 10 
Product Version0.18 
Target Version0.20 
Summary0004154: Parametric constraint can be changed only one way for fully constrained sketch
DescriptionI've a sketchup drawing with named constraints. Increasing the constraint value works, decreasing it does not. (Increasing to a value and then trying to change back is broken too).

I've encountered this bug in many forms, if the R is not a radius constraint but one of the length constraints (see file 2), it's not possible to change the value AT ALL.
Steps To Reproduce1. Open attached file
2. Open sketcher with the "Sketch"
3. Change constraint R to 4mm
4. Change constraint R back to 3mm

Observe error: Negative datum values are not valid for the constraint with index 10 (That is the R constraint).

Expected: Change back obviously.
Additional InformationOS: Windows 10
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.18.16131 (Git)
Build type: Release
Branch: releases/FreeCAD-0-18
Hash: 3129ae4296e40ed20e7b3d460b86e6969acbe1c3
Python version: 3.6.6
Qt version: 5.6.2
Coin version: 4.0.0a
OCC version: 7.3.0
Locale: English/UnitedKingdom (en_GB)
FreeCAD Information



2019-10-05 23:03


bug1.FCStd (12,451 bytes)
bug2.FCStd (12,465 bytes)


2019-10-07 10:46

developer   ~0013719

Last edited: 2019-10-07 10:52

@axos88 thanks for reporting. According the guidelines (big yellow box on top of page), could you please first post to forum so your findings can be discussed ?
Notice that despite what you found can lead to interesting corner case tests, your sketch is very very lamous. It's highly suboptimal, and I could have bet just by seeing it that it can seriously hurt the solver. :)

EDIT : JFYI, you're cumulating 2 known corner cases.
1 - Setting equal radius and horizontal/vertical distance on an arc
2 - Having tangent arc/line obtained by construction but not by constraint


2019-10-07 17:02

reporter   ~0013724

@openBrian, thanks for getting back to me. Sorry for not asking in the forum first, I understood it's for verifying and prefiltering wether reports are actually bugs, and it was pretty straightforward that this is.

I'll do that now, I'm curious why my sketch would be lamous and suboptimal and to learn how to do it better.

I'm not sure I understand the second corner case you mentioned, but I'm sure I'll get an answer there.


2019-10-07 17:09

developer   ~0013725

@axos88 actually the problem with direct reporting is that there is high chance that your "bug" is known & already reported. ;) Also it can be a known limitation.
Once you open a forum topic, may you please cross-reference it in this ticket ? Thx


2019-10-07 17:13

reporter   ~0013726

Once it gets approved, and I get a link to it, yes, of course.


2020-10-08 01:12

administrator   ~0014790

@axos88 link to forum thread?


2022-03-03 13:55

administrator   ~0016828

This ticket has been migrated to GitHub as issue 5994.

Issue History

Date Modified Username Field Change
2019-10-05 23:03 axos88 New Issue
2019-10-05 23:03 axos88 File Added: bug1.FCStd
2019-10-05 23:03 axos88 File Added: bug2.FCStd
2019-10-07 10:46 openBrain Note Added: 0013719
2019-10-07 10:47 openBrain Status new => feedback
2019-10-07 10:47 openBrain Description Updated
2019-10-07 10:47 openBrain Steps to Reproduce Updated
2019-10-07 10:47 openBrain Additional Information Updated
2019-10-07 10:48 openBrain Tag Attached: #post-to-forum
2019-10-07 10:52 openBrain Note Edited: 0013719
2019-10-07 17:02 axos88 Note Added: 0013724
2019-10-07 17:02 axos88 Status feedback => new
2019-10-07 17:09 openBrain Note Added: 0013725
2019-10-07 17:13 axos88 Note Added: 0013726
2019-10-07 18:12 openBrain Tag Detached: #post-to-forum
2019-10-07 18:12 openBrain Tag Attached: #pending-forum
2020-10-08 01:12 Kunda1 Note Added: 0014790
2021-02-06 06:49 abdullah Target Version => 0.20