Sketcher / Solver issue

[Hannu]

Straight to the issue:

Open FreeCAD,
create a new document,
create a Part, Body
and start a Sketch.

Create a rectangle to the left of the Origin, make it 10mm high, attach e.g. lower right corner to the Origin.
Create a Circle, set radius to be 10mm.
Move it to make one third of it cover the left end of the rectangle.
Select "Trim" and click on the portions of the rectangle's horizontal lines that are inside the circle; these disappear.
Click on the segment of the circle that is between the horizontal lines of the rectangle.
Remove the remaining vertical line which was part of the rectangle; click on it and hit Delete

What remains is in practice "()="

At this point you can push and pull the horizontal lines, and the circle center and the sketch behaves quite rationally.

Now add fillets to both the left ends of the horizontal lines and the circle (=segment).
Set Equality from the circle to the fillets.


You should have something similar to:

Screenshot from 2021-03-28 09-10-48.png (16.37 KiB) Viewed 1213 times

Now again push/pull on the horizontal lines and the circle center (with long movements);
you will notice the behavior is not as nice as above.


---
OS: Ubuntu 20.04.2 LTS (ubuntu:GNOME/ubuntu)
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.19.
Build type: Release
Branch: unknown
Hash: e8566f22bbeb0b7204e3c45519d0963e8881100b
Python version: 3.8.5
Qt version: 5.12.8
Coin version: 4.0.0
OCC version: 7.5.1
Locale: English/United States (en_US)

[chrisb]

I can't see anything wrong. If you want to have the horizontal lines equal, set an equality constraint.

[HarryGeier]

The Problem is :

Equality for a circle / arc means same radius and center point, not same start/end points.
Same is for a line or the like..it has teh same length , but still can be anywhere in space.



Set the 2 intersect points to the lines to be constrained vertically and all is well..

Harry

[Hannu]

Now again push/pull on the horizontal lines and the circle center (with long movements);
you will notice the behavior is not as nice as above.

Pulling and pushing the Horizontal lines or (e.g. the center of) the circle produces "positions" similar to this:

Screenshot from 2021-04-04 11-25-58.png (27.6 KiB) Viewed 1086 times

Similar things can happen as you add constraints or move items around in a sketch while working on it.

CTRL-Z often puts things back where they were;
but the operation you attempted (to get further in your work) is likely to re-create it,
unless you find a way to circumvent the problem - which isn't always EASY.

Suggestion; NOTE - discussion material:
Temporarily record the current circle (segment), just before any change is applied;
Make sure it's center stays (within the circle?) oriented the same way / direction as it was while any changes are calculated and applied.

[Hannu]

The Problem is :

Equality for a circle / arc means same radius and center point, not same start/end points.
Same is for a line or the like..it has teh same length , but still can be anywhere in space.

Set the 2 intersect points to the lines to be constrained vertically and all is well..

Harry

I'm not sure what you're trying to tell here;
my point is NOT to stabilize the shown "thingy".

I'm trying to use the "simplest possible setup" to show a problem.