Difficulties in using A2Plus to attach faces

[tadinltd]

OS: Windows 10 Version 2009
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.19.24267 +148 (Git)
Build type: Release
Branch: Branch_0.19.4
Hash: 476ecf091941bead59b14e44afa6064d5a66afa3
Python version: 3.8.6+
Qt version: 5.15.2
Coin version: 4.0.1
OCC version: 7.5.3
Locale: English/United Kingdom (en_GB)

I have been playing with FreeCad for some time, most times it was easy, other times quite difficult, but generally it is a beautiful tool.
I have now a seemingly easy task, namely to build a square frame out of 4 identical elements, each cut at 45 deg. The elements were created in PartDesign and copied 3 times, so they all are identical (but not necessarily at the same plan!).
The A2Plus seems to be the right tool. I imported the elements and used the planeCoinsident Constraint to match and attach the small 45 deg. faces, but unfortunately, as can be seen in the attached I could not make it work. (It did work one time, but I can't repeat it)
I need help in either showing me how to do it with the A2plus or suggest a better / different way to accomplish.

[chrisb]

Moved from Help forum.

[tadinltd]

Thanks chrisb
Although I have been using FreeCad for some time (sporadically), I am far from being a knowledgeable user.
The question was not in the sketch domain but rather in the A2Plus, where faces that I expected to join did not beave that way.
I found ways arround, but the question still remains the same. Why they do not move to the expexted position?
If the problem was in the originating sketch, can you please show me what did I do wrong?

[Laurie Hartley]

Thanks chrisb
Although I have been using FreeCad for some time (sporadically), I am far from being a knowledgeable user.
The question was not in the sketch domain but rather in the A2Plus, where faces that I expected to join did not beave that way.
I found ways arround, but the question still remains the same. Why they do not move to the expexted position?
If the problem was in the originating sketch, can you please show me what did I do wrong?

My workflow would be:-

Open member 1 and make sure that its position is fixed (see combo view snip)
Import 3 more members using the duplicate icon (see snip)
Use the transform tool to rotate them 90 degrees and closer to the intended joint. (see snip)
If you wish use the face constraint but this will only place them in the same plane
I would use the point constraint
Make sure your newly attached member is made to be in "fixed" position from combo view.
Use the point constraint to attach the remaining two members ALWAYS attaching to a fixed member.

[dan-miel]

Use the transform tool to rotate them 90 degrees and closer to the intended joint. (see snip)

Tadinltd,
Laurie’s process will work but if a part gets rotated the part may not return to the position you want it in. It may be better to use all A2+ constraints, instead of using the transform tool, use the A2+ plane Constraint to line up the 45 degree angles then the point constraint to lock the parts in place. This way if the parts become rotated they will return to the correct position.
Side note: Your file has all three constraints on one surface. Normally you need thee constraints to locate a part in the three axes, One constraint for x, one for y and one for z. Using the point constraint locates the position of the point but not the rotation of the part.
Dan

[Laurie Hartley]

I am still learning 5 years on Dan One question from me:-

Is part of Tadinitd’s problem caused perhaps by him trying to constrain two “non fixed parts”?

[dan-miel]

Is part of Tadinitd’s problem caused perhaps by him trying to constrain two “non fixed parts”?

Laurie:
This is a simple question but the answer is not so simple. My short answer would be No, but other people may answer differently. Any software that I have used does not consider non-fixed parts a problem. They seem to build the non-fixed parts as if the first non-fixed part was fixed. It might look like a sub assembly and when you added a constraint to a fixed part the constraint would pull everything together. A2+ gives an error message but I ignore the message even though a newer user may need the message to alert them why the parts are not moving or assembling the way they expect.

I am still learning 5 years on

Spent 25 years on 3D modeling and only scratched the surface.
Dan

[Laurie Hartley]

@dan-miel Thanks for your answer Dan.

[tadinltd]

Hi,
Being the originator of this thread, my issues were partially solved thanks to some remarks made mainly by Laurie Hartley. Thanks Laurie.
Yet, with planeCoinsident (as with any other), there is more than one possible direction to the attachement and one has to be creafull or use several constraints to assure permanent repetable positioning. (a single point constraint has endless possibilities!).
As for the "fixed" position question: The first one must be "fixed". Do I have to make the second item fixed as well to attach the third one to it?
Another issue I noticed is that when importing items to the A2P, they keep their original coordinates from the original file. Is this a correct behaviour? I would have thought they should get the new A2P coordinates! ( I briefly tried the MoveToOrigin macro, but did not get it to work).

[dan-miel]

with planeCoinsident (as with any other), there is more than one possible direction to the attachement and one has to be creafull or use several constraints to assure permanent repetable positioning. (a single point constraint has endless possibilities!).

Hi Tadinltd. Try the following:
Add the fixed part and part 1.
Using the Axis Coincident Constraint constrain the sharp edge of the parts along the red dotted line. You may need to flip the constraint.
Use the Plane constraint on the two 45 degree faces “B”.
Mate the top “C” faces with the Plane constraint.
Repeat the last three lines with the other pieces.
The axis constraint allows only two possibilities for the part position. The other constraints will be good.

As for the "fixed" position question: The first one must be "fixed". Do I have to make the second item fixed as well to attach the third one to it?

Only one part in an assembly should be fixed.

I hope this helps.
Dan
edit: Added picture