Merge Sketches is distorting the sketches

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ChrisFC
Posts: 27
Joined: Mon Jul 26, 2021 8:30 am

Merge Sketches is distorting the sketches

Post by ChrisFC »

Hi all,

I have 3 quadrilaterals, each their own sketch. In each sketch, I have both vertical and horizontal constraints fixing the position (or so I thought!) of each of the corner points, such that these points should not ever be moveable. Each quad is somewhere in (X,Y,Z) (ie they dont all just lie on one of the coordinate planes.

I need to combine these 3 sketches, and after selecting them and clicking on 'merge sketches', I get a single sketch, however, 2 of my quads in this new combine sketch are absolutely no where near where they should be now and have randomly moved to a new place. I cannot for the life of me figure out why this is happening. It is imperative in my sketch that these corner points do not move at all.

Any ideas on why this may be happening? Could it be that the corner point's horizontal and vertical position constraints are not being carried over when combined into the new sketch? Also, whenever I seem to make the horizontal position constraint, it only ever seems to be a distance constrained from the y axis, not the x axis. Ideally I just want the absolute position of the points to be fixed; any ideas?

Cheers,
Chris

FreeCAD v 0.19 using the Ubuntu AppImage
domad
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Re: Merge Sketches is distorting the sketches

Post by domad »

ChrisFC wrote: Mon Dec 06, 2021 3:31 pm .....
Hi ChrisFC, hello to the Community!

For a concrete answer it is always better to attach the file or a different file that in any case re-proposes the problem, at least some screens that show it.
ChrisFC
Posts: 27
Joined: Mon Jul 26, 2021 8:30 am

Re: Merge Sketches is distorting the sketches

Post by ChrisFC »

domad wrote: Mon Dec 06, 2021 4:38 pm
ChrisFC wrote: Mon Dec 06, 2021 3:31 pm .....
Hi ChrisFC, hello to the Community!

For a concrete answer it is always better to attach the file or a different file that in any case re-proposes the problem, at least some screens that show it.
Hi Domad!

Unfortunately I am not able to do so for IP related reasons
chrisb
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Re: Merge Sketches is distorting the sketches

Post by chrisb »

I'm afraid there is no simple solution to your task. To be sure:
- You have sketches in different planes in 3D space
- the sketches use external references

If you combine these sketches into one, then the shape will be distorted, because they will keep their original references to external geometry.
There are no 3D sketches, which would be required if all sketches should keep their old state.
A Sketcher Lecture with in-depth information is available in English, auf Deutsch, en français, en español.
ChrisFC
Posts: 27
Joined: Mon Jul 26, 2021 8:30 am

Re: Merge Sketches is distorting the sketches

Post by ChrisFC »

chrisb wrote: Mon Dec 06, 2021 5:00 pm I'm afraid there is no simple solution to your task. To be sure:
- You have sketches in different planes in 3D space
- the sketches use external references

If you combine these sketches into one, then the shape will be distorted, because they will keep their original references to external geometry.
There are no 3D sketches, which would be required if all sketches should keep their old state.
Hi there Chris,

I think perhaps I can show this which may help (I suspect you may have hit the nail on the head)

Of my 3 sketches, 2 distort when merged. Pre-merge, this is the plane associated with those said 2 sketches:
Screenshot from 2021-12-06 17-10-12.png
Screenshot from 2021-12-06 17-10-12.png (24.12 KiB) Viewed 1781 times
Looking at this plane, it is not aligned with the xy plane. For context, I made these sketches after having revolved some CAD around the Z axis, taking a cross sectional slice of said rotated CAD, before making said cross section into a sketch.

The 1 sketch of the trio that doesn't distort when merged has a plane like this that is aligned with the xy plane and did not come about from rotation
Screenshot from 2021-12-06 17-13-46.png
Screenshot from 2021-12-06 17-13-46.png (21.4 KiB) Viewed 1781 times
Is it due to these planes being differently oriented? And if so, is there a work around?

Cheers,
Chris
TheMarkster
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Re: Merge Sketches is distorting the sketches

Post by TheMarkster »

What are you trying to do, exactly? Perhaps there is a better way instead of using merge sketches, which is non-parametric.
ChrisFC
Posts: 27
Joined: Mon Jul 26, 2021 8:30 am

Re: Merge Sketches is distorting the sketches

Post by ChrisFC »

TheMarkster wrote: Mon Dec 06, 2021 5:27 pm What are you trying to do, exactly? Perhaps there is a better way instead of using merge sketches, which is non-parametric.
What I am doing in a nutshell is taking a creating a FreeCAD file where I can quickly make changes to some CAD that I'm working on.

Said CAD exists in 3D toroidal space, and is essentially a 2D profile in the centre of the CAD (that can be changed), which is to be swept down to a set of known end faces of said part. By creating sketches for a) the middle cross section, and b) the 2 end cross sections, I had hoped to make life easier for myself. Part of my work will involve creating a circle through both the middle cross section, as well as a point on either end face, such that I will be able to define a surface which will act to shape the top section of the CAD. So far I have a nice sketch for the middle cross section wherein I can easily change the shape of said cross-section in a way suitable for my work. I then intended to link these 2 sketches together such that I could add the aforementioned circle between the middle and end cross sections. I had hoped that by doing so in a sketch I could constrain the end faces to be fixed/unchanging, and instead change the middle cross section and automatically change the circle that connects the 2. I wanted to create said circle through 3 points, which looks like something that FreeCAD can do quite easily, however, each of those points presently sits in their own sketches, hence wanting to create a single sketch.
TheMarkster
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Re: Merge Sketches is distorting the sketches

Post by TheMarkster »

Without the file it's guesswork, but you might be able to create a 4th sketch and use links to external geometry to get the 3 points from the other 3 sketches and create the circle based on those links to external geometry.
ChrisFC
Posts: 27
Joined: Mon Jul 26, 2021 8:30 am

Re: Merge Sketches is distorting the sketches

Post by ChrisFC »

TheMarkster wrote: Mon Dec 06, 2021 7:36 pm Without the file it's guesswork, but you might be able to create a 4th sketch and use links to external geometry to get the 3 points from the other 3 sketches and create the circle based on those links to external geometry.
I just want to know how I can make it so that the construction planes (as shown in my above post) are not slanted and are the same as the top one (xy plane). At this point this is what I would like to know, as this seems to be the issue.
domad
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Re: Merge Sketches is distorting the sketches

Post by domad »

ChrisFC wrote: Mon Dec 06, 2021 8:56 pm ........
I just want to know how I can make it so that the construction planes (as shown in my above post) are not slanted and are the same as the top one (xy plane). At this point this is what I would like to know, as this seems to be the issue.
Hi ChrisFC, hello to the Community!
The * .gif shows two of the different ways to be able to align two sketches (but it could be any other object) arranged randomly in 3D space, the first involves the use of the "Alignment" function, the second (applicable in any case) provides the 'use, Wb "Draft, of the transformation tools (movement and rotation) supported by the snaps functions and of the setting of the work plane.
Attachments
alignment.gif
alignment.gif (980.33 KiB) Viewed 1543 times
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