Symmetry constraint issue

[avid]

Hi

I'm trying to create a symmetry constraint but i get an error and i don't understand what i'm doing wrong.
I select two point and Y axis then click on the symmetry button and get this:

Untitled.png (216.94 KiB) Viewed 514 times

attached the Freecad file before the symmetry (

test.FCStd

(5.7 KiB) Downloaded 7 times

) and with the symmetry error (

test1.FCStd

(6.11 KiB) Downloaded 8 times

)


OS: Windows 10 Version 2009
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.19.24276 (Git)
Build type: Release
Branch: releases/FreeCAD-0-19
Hash: a88db11e0a908f6e38f92bfc5187b13ebe470438
Python version: 3.8.6+
Qt version: 5.15.1
Coin version: 4.0.1
OCC version: 7.5.0
Locale: Hebrew/Israel (he_IL)

[Bance]

By applying the symmetry constraint the horizontal is implicit, thus already having a horizontal constraint shows as over contraining.

Delete the horizontal constraint.

Read Chrisb's sketcher lecture, a link is available in any one of his posts.

In the future please include the information as laid out in the posting rules. (^^BIG PINK BANNER^^)

[jmaustpc]

I'm trying to create a symmetry constraint but i get an error and i don't understand what i'm doing wrong.

It tells you both what is wrong (you have inserted redundant constraints) and suggests which constraint (5) the problem likely relates to.

In this case it is because that constraint 5 is a Horizontal constraint but symmetry constraint applied to the vertical axis already forces the line to be horizontal, mathematically the line defined by two points in symmetry around a line must be at right angles to it.

Note that this does not apply to symmetry around a point, e.g. origin. which can be at any angle.

If it makes you feel better, I can assure you that you are not the first to have been confused by this.

By the way, if you were intending to apply another symmetry to the other axis and hence make your rectangle centred on the origin point, then there is a better way. Leave the Horizontal and vertical constraints there, then select only two diagonally opposed points and origin then apply only that one symmetry and you will have centred you rectangle.

Jim

posted at the same time as Bance, pretty much says the same thing.

[avid]

It seems that when i check the "auto remove redundants" is give the ability to make a symmetry constraint.

Thank you

[chrisb]

It seems that when i check the "auto remove redundants" is give the ability to make a symmetry constraint.

If you look what it does: it is exactly doing what is proposed, it removes the horizontal constraint. I don't recommend to check this box. It is convenient, yes, and in this case it does what I would do anyway. But sometimes it removes a constraint which I would definitely keep, and where it would have been far better to remove something else.