How to think around midpoint snapping

[run_the_race]

There are many posts about snapping to the mid point of an item. The general answer you can do the same without them. So I am trying, but I think I need a little eye opening.

In the below *Sketcher* example, I wish to place the rectangle vertically and horizontally centered between the two circles.

midpoint snapping.png (11.62 KiB) Viewed 467 times

In solid edge 2D drafting I would draw a diagonal construction line on the rectangle, then snap the mid point of the diagonal to the mid point of a construction line between the two circles.

So now without midpoint snapping. I can create a symmetric constraint to center it vertically by selecting the line between the circles and the two points circle in green below:

midpoint sym.png (13.19 KiB) Viewed 467 times

Now I cant think of a idiomatic way to center it horizontally. How would you center the rectangle horz/vert between the two circles?

Code: Select all

OS: Windows 10 Version 2004
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: English/United Kingdom (en_GB)

[drmacro]

add a point object to each construction line
add symmetry constraints to the point with the ends of its associated line
add point coincident between the point objects


just a guess...not at a pc ATM.

[jmaustpc]

one very simple option.
1) create a "point" roughly in the middle of the rectangle
2) select firstly two diagonally opposing end points of the rectangle, then select the point near the centre
3) click on symmetry constraint.
4) select each centre of the two circles and then the "point", then click symmetry constraint again

Jim

we posted much the same thing at the same time.

[Syres]

A pciture is worth a thousand words but the thing to note is the use of two diagonal construction lines both parallel and equal (praise to @Celica_Supra aka Joko Engineering for bringing this to my attention in his Cylinder Head tutorial):

Rect_inBetween_Circles.jpg (49.02 KiB) Viewed 452 times

OS: Windows 7 Version 6.1 (Build 7601: SP 1)
Word size of FreeCAD: 64-bit
Version: 0.20.24694 (Git)
Build type: Release
Branch: master
Hash: 111a21e45cd63e0d84b5c16e09ad599712ee11ae
Python version: 3.8.6+
Qt version: 5.15.1
Coin version: 4.0.1
OCC version: 7.5.0
Locale: English/United Kingdom (en_GB)

[run_the_race]

add a point object to each construction line
add symmetry constraints to the point with the ends of its associated line
add point coincident between the point objects

just a guess...not at a pc ATM.

Thanks for that suggestion. When I add the extra point on the construction line, and then try add the symmetry constraint to the 3 points, it gets messed up. How does it know which points need to be symmetrical around which other point, and along which axis? I guess you need a line for the symmertry axis, but that is what we are trying to create. Chicken egg scenario.

[jmaustpc]

here is a demo file

demo_align_retangle_circle_centres_by_symmetry_with_point.FCStd

(16 KiB) Downloaded 7 times

and a screen shot of the sketch in edit mode fully constrained.

Just note that with symmetry, selection order is important, you must select the geometry that is to be the centre of the symmetry last.

Screenshot_20210420_215647.png (68.76 KiB) Viewed 449 times

Jim

OS: Ubuntu 20.04.2 LTS (KDE/plasma)
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.19. stable PPA
Build type: Release
Branch: unknown
Hash: 9e3b630bbfb6807e93eeffb655e6c20f218644fc
Python version: 3.8.5
Qt version: 5.12.8
Coin version: 4.0.0
OCC version: 7.5.1
Locale: English/Australia (en_AU)

[jmaustpc]

add a point object to each construction line
add symmetry constraints to the point with the ends of its associated line
add point coincident between the point objects

just a guess...not at a pc ATM.

Thanks for that suggestion. When I add the extra point on the construction line, and then try add the symmetry constraint to the 3 points, it gets messed up. How does it know which points need to be symmetrical around which other point, and along which axis? I guess you need a line for the symmertry axis, but that is what we are trying to create. Chicken egg scenario.

To be clear, you do not need the construction line at all.

the centre of the symmetry can be either a point or a line.

The "centre" of the symmetry is just whatever you selected last. The first two selections are the object to be symmetrical around the third selected item.

If you just hold your mouse point over the symmetry icon, the tool tip will tell you this.

Jim

[run_the_race]

one very simple option.
1) create a "point" roughly in the middle of the rectangle
2) select firstly two diagonally opposing end points of the rectangle, then select the point near the centre
3) click on symmetry constraint.
4) select each centre of the two circles and then the "point", then click symmetry constraint again

Jim

we posted much the same thing at the same time.

Brillant, that worked very well! Thank you! The key point here is the order in which one select points for symmetry. Might be useful to have prompts in the bottom bar ("select point, select other point, select symmetry axis or point")... I have seen that in other SW.

[run_the_race]

If you just hold your mouse point over the symmetry icon, the tool tip will tell you this.
Jim

Oh I see that is very nice to have that documented there, great!

[drmacro]

I see @jmaustpc has got you going.

As noted the construction lines are superfluous in this instance.