# Understanding Constraints
**URL:** https://discourse.shapr3d.com/t/understanding-constraints/31752
**Category:** Modeling Questions
**Created:** [May 8, 2024, 3:11am UTC](https://discourse.shapr3d.com/t/understanding-constraints/31752 "2024-05-08T03:11:43Z")
**Posts on this page:** 10
**Page:** 1
### Author:  [@UCS308](https://discourse.shapr3d.com/u/UCS308)
#### Post date: [May 8, 2024, 3:11am UTC](https://discourse.shapr3d.com/t/understanding-constraints/31752/1 "2024-05-08T03:11:43Z")
I am trying understand constraints when sketching. I am having trouble with this dovetail that will form part of a leg. When i try and change the width the dovetail distorts. I built it twice once with both halves and once as you see it here. In neither case will the dimensions of the dovetail remain.
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### Author:  [@Steve](https://discourse.shapr3d.com/u/Steve)
#### Post date: [May 8, 2024, 3:53am UTC](https://discourse.shapr3d.com/t/understanding-constraints/31752/2 "2024-05-08T03:53:46Z")
Short answer – computers are stupid, or at least very literal. You need to tell it exactly what you don’t want it to change.
Which might be a LOT of constraints, possibly:
angle of each side (or mirrored, etc.)
height
width
distance from sides or center, etc.
maybe other dimensions that must not change
or any combination
There are almost always multiple ways to lock things down – some more efficient than others depending on the situation. For example,
mirrored to a centerline
equal length
specified distance
but you will almost certainly need multiple constraints to achieve your goal.
[https://www.youtube.com/watch?v=W4MKAuDJ\_I8&pp=ygUQc2hhcHIzZCBiZXZlbGlzaA%3D%3D](https://www.youtube.com/watch?v=W4MKAuDJ_I8&pp=ygUQc2hhcHIzZCBiZXZlbGlzaA%3D%3D)
This is a pretty good link about furniture design and he covers a lot of info about constraints.
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### Author:  [@shape-it](https://discourse.shapr3d.com/u/shape-it)
#### Post date: [May 8, 2024, 10:21am UTC](https://discourse.shapr3d.com/t/understanding-constraints/31752/3 "2024-05-08T10:21:08Z")
Hello Steve,
You seem to be an experienced Shapr user, so I’m responding to this post. Maybe you can help me. We work a lot with existing drawings of complex profiles (the one in my video is not really complex yet). Since the new capabilities with the parametric system offer many advantages, I need and want to delve deeper into it (so I see the clear advantages!). To make it easier to adjust changes based on sketches in the future, I want to be able to move existing drawings by new specifications, in this case, just to the right.
So, I make a line in the middle of the sketch so that I can use it as an axis point. However, I can’t simply redefine the distance after the copy using this line, as all other lines would distort. Would I then really need to fix all dependencies so that this sketch does not shift? Is there a simpler way, similar to locking? Therefore, we tend to use the pattern function more, but it’s really just a workaround and only works with equal distances.
Thanks in advance!
Cheers
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### Author:  [@Xdrakosha](https://discourse.shapr3d.com/u/Xdrakosha)
#### Post date: [May 8, 2024, 3:38pm UTC](https://discourse.shapr3d.com/t/understanding-constraints/31752/4 "2024-05-08T15:38:27Z")
> [@shape-it](#):
>
> Is there a simpler way, similar to locking?
I don’t see another way but add enough constraints to keep sketch shape during moving.
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### Author:  [@UCS308](https://discourse.shapr3d.com/u/UCS308)
#### Post date: [May 9, 2024, 4:09am UTC](https://discourse.shapr3d.com/t/understanding-constraints/31752/5 "2024-05-09T04:09:59Z")
Is this a response to my post? Or the other post?
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### Author:  [@Xdrakosha](https://discourse.shapr3d.com/u/Xdrakosha)
#### Post date: [May 9, 2024, 4:35am UTC](https://discourse.shapr3d.com/t/understanding-constraints/31752/6 "2024-05-09T04:35:53Z")
> [@UCS308](#):
>
> Is this a response to my post? Or the other post?
That was replay to previous post 🙂
To answer your question with more details, then Steve already gave, you have to provide more info about what exactly you trying to achieve.
Here is example, you can see which constrains I used.
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### Author:  [@UCS308](https://discourse.shapr3d.com/u/UCS308)
#### Post date: [May 9, 2024, 5:03am UTC](https://discourse.shapr3d.com/t/understanding-constraints/31752/7 "2024-05-09T05:03:42Z")
@Steve Thanks. I watched that Bevelish video before posting. And some of what he shows will help. Especially the portions on stretchers.
But I did not find a solution for keep the edge of the piece (leg) and the tip of the dovetail, inline. I tried a construction line. I tired symmetry. I am not practiced enough using sketches and constraints, to know if this is a bug, or just not possible.
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### Author:  [@UCS308](https://discourse.shapr3d.com/u/UCS308)
#### Post date: [May 9, 2024, 5:40am UTC](https://discourse.shapr3d.com/t/understanding-constraints/31752/8 "2024-05-09T05:40:25Z")
I redrew my ‘leg’ sketch. I don’t recall doing it any differently and it almost works. But I removed a coincident constraint by mistake and now I am trying to add them back and I never get the option. I wonder if coincident constraints can’t be added after.
Here is a screen recording of resizing the width of the leg sketch and you can see the top - left corner comes apart. What is the best way to constrain that?
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### Author:  [@Xdrakosha](https://discourse.shapr3d.com/u/Xdrakosha)
#### Post date: [May 9, 2024, 5:50am UTC](https://discourse.shapr3d.com/t/understanding-constraints/31752/9 "2024-05-09T05:50:30Z")
> [@UCS308](#):
>
> I am trying to add them back and I never get the option.
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### Author:  [@UCS308](https://discourse.shapr3d.com/u/UCS308)
#### Post date: [May 9, 2024, 6:11am UTC](https://discourse.shapr3d.com/t/understanding-constraints/31752/10 "2024-05-09T06:11:57Z")
THANK-YOU… Constraints are by far the trickiest part of the Shapr UI. Now I can resize the proportion of the leg and the dovetail angles and proportion remains the same.