topic Re: Coincident constraint not working as expected in AutoCAD Forum

Coincident constraint not working as expected

ajehresmann — Tue, 08 Mar 2022 18:35:23 GMT

I'm trying to get one line to coincide with another on a drawing so it stretches when I change the dimension size but its not moving, it's acting like it's a fixed length line and I'm not sure why. I've tried tinkering around with it but nothings worked. Does anyone know what could be the reason for this? I've attached some screenshots of what I'm looking at to help.

[This post has been edited for clarity by cheryl.buck]

Re: Coincident constraint not working as expected

cheryl.buck — Tue, 08 Mar 2022 18:54:07 GMT

Hi @ajehresmann,

It is kind of hard to tell what the problem is from just images, but I would guess it is over constrained, possibly from the constraints of a neighboring object.

If you want to post your file in the thread, and specify which line the issue is occurring with, we can take a look.

All the best,

Re: Coincident constraint not working as expected

ajehresmann — Tue, 15 Mar 2022 17:59:10 GMT

Hi @cheryl.buck thanks for getting back to me.

I was thinking it might be an over constraint issue too but when I opened the file today the line that wasn't acting how I expected it to started working like I thought it would and I'm not sure why, but maybe it was just a fluke glitch.

I'm not sure either still of how to get my annotations to respond parametrically like how to keep the center lines on the front of the hole when I change the dimensions. I've tried combing perpendicular and colinear constraints but that's not acting how I want it to and tried to add a tangent constraint but it won't let me cause then it says it'll be over constrained. I don't know if that's something you can help with but I'd appreciate any insight that could be offered.

I attached the acad file below.

Thanks again

[This post has been edited for clarity by cheryl.buck]

Re: Coincident constraint not working as expected

cheryl.buck — Tue, 15 Mar 2022 18:20:33 GMT

Hi @ajehresmann,

Thank you for the file and screen shots. I apologize for my delay, I am generally only in the forums on Tuesdays.

I was able to check the file, and do not immediately see any conflicts between the constraints, but agree that adding tangents would over constrain it.

On the centerlines not showing in front of the hole, I don't believe I am seeing the same thing. However, I also may not be following precisely the same steps as you are when you see it. Can you provide a screen share showing the steps leading up to the issues?

One thing I can offer from my experience, is that when I encounter constraint conflicts or unexpected behavior, deleting and rebuilding the constraints often resolves the issue entirely. My suspicion is that I have accidentally left a constraint in, or constrained more lines than I intended in one.

All the best,

Re: Coincident constraint not working as expected

ajehresmann — Sat, 19 Mar 2022 21:54:42 GMT

Hi @cheryl.buck

Thanks for taking the time to look over my work.

I think my main problem got solved by just closing and reopening the file later which might've rebuilt it like you suggested.

The other problem I'm trying to figure out though is how to have both centerlines on a hole face move with the hole circle instead of one just staying in place and the other moving with the hole. They're both showing up just not moving parametrically like I want and I'm not sure how to constrain them so that they do. The other screencaps I gave show what I'm talking about but I attached a couple more here to hopefully clarify what I'm trying to fix.

Thanks again for all your help!

Re: Coincident constraint not working as expected

j.palmeL29YX — Mon, 21 Mar 2022 17:11:48 GMT

@ajehresmann wrote:

The other problem ...

>>Here<< a suggestion how to repair this issue (constrain the midpoints of both centerlines to the center point of the circle and constrain the lengthen of both centerlines). ([EDIT]: corrupt link repaired)

I found a lot of other problems/missing constraints in your model. One of them (the most left vertical line) I also repaired in the video).

Re: Coincident constraint not working as expected

j.palmeL29YX — Fri, 25 Mar 2022 05:58:06 GMT

Sorry, I could not resist. 😉

Attached a suggestion how I would (full) constrain your model.

Some tips:

- If you have lines connected endpoint to endpoint, use polylines as much as possible. So you can avoid a lot of coincident constraints between the separate line endpoints.

- Try to avoid redundant constraints. But add as much constraints as you need to get a stable shape.

- At last add the needed dimension constraints.

The final goal must be a geometry which is full constrained. No possibilities for change may remain that are not intended.

You can easily >>check this<< using the block editor. Create a (test) block and activate the BCONSTATUSMODE. In my settings the full constrained geometry will be blue (you can change this colors as you wish).

In my example at first only one of the views seems to be full constrained. Why? Because we can still can move the other both views horizontally/vertically. This is ok, but for testing we must constrain this possible movement too, e.g. adding two dimensional constraints. Now all ist blue and we can be rather sure that the model is full constrained.

Re: Coincident constraint not working as expected

j.palmeL29YX — Tue, 22 Mar 2022 17:58:11 GMT

Above I wrote a recommendation "The final goal must be a geometry which is full constrained".
Why? We can never know in which way a user will try to modify the model. An example on the file you posted shows in >>this video<< that a small manipulation on a not fully determined geometry can destroy the whole model. 😞

Unfortunately I too posted a file that does not fully comply with this recommendation. On closer inspection (while the "block editor" test) I should have noticed it. See >>this video<<. But by adding one constraint (perpendicular to the other line or horizontal or collinear or parallel ..., a lot of possibilities) this can be easily corrected.

Let me/us know if you have further questions.

If my reply solves your problem, click the "accept as solution" button. This can help others find solutions faster

Re: Coincident constraint not working as expected

ajehresmann — Thu, 07 Apr 2022 23:43:42 GMT

Hi @j.palmeL29YX

Thank you so much for your above and beyond response, it really helped me get a better grasp on how parametric constraints work and I hate to ask for anymore of your time and effort but I'm still a little confused one some things if you don't mind explaining a bit more for the sake of complete understanding. Specifically, how the centerlines on the front and top views are made parametric, I think it's due to the vertical point constraints on the ends but I'm not sure why that works if so. And how you made the drill hole and its hidden view on the front and right views move together with geometric constraints. I'm not sure exactly how yours works but I redid mine using tangent constraints on the hidden lines and drill hole but your method is surely much cleaner and efficient so I want to know how it ideally should work. I attached a dwg file of my second attempt below and I'm not sure if your original videos had audio but just to make sure there's not a problem, when I watched your screencasts I couldn't unmute them.

Thanks again for being so helpful I really appreciate it.

Re: Coincident constraint not working as expected

j.palmeL29YX — Fri, 08 Apr 2022 16:37:12 GMT

Not yet "perfect", but good enough for use. 😉

>>What I'd still do: << (My videos are without audio narration).

First I added a dimension d5. I think you only forgot it.

The only remaining "problems" are now the centerlines.

In the right view I'd suggest to use coincident constraints between the centerpoint of the circle and the midpoints of the centerlines. So they are always symmetrical to the circle.

I added a dimension d7 depending of the dia1 for their length and set the both to be equal length.

In the front view I added a dimension for the extension of the centerline. To get it symmetrical I added a vertical constraint between the midpoint of the center line and the midpoint of the edge above.

The same method (vertical constraint between two points) I used to fix the length of the centerline in the top view.

(Instead, i could have added 3 more dimensions for the extensions. But I prefer first to constrain as much as possible with geometrical constraints, and only the remaining with dimensional constraints).

A lot of other ways are possible to get the whished result. Which is the "best"? I think no one can say it. I try to make calculations as easy as possible for the computer, e.g. I'd prefer a coincident constraint over a tangential constraint. But if this is really advantageous? I don't know, I do it by feeling.

Re: Coincident constraint not working as expected

j.palmeL29YX — Sat, 09 Apr 2022 04:26:11 GMT

@ajehresmann wrote:

And how you made the drill hole and its hidden view on the front and right views move together with geometric constraints. I'm not sure exactly how yours works

>>Here<< a video how I'd do it (and similar did it above). [Video link EDITed]

@ajehresmann wrote:

I hate to ask for anymore of your time and effort but I'm still a little confused one some things

Feel free to ask again if you have further questions. We're glad to help others ...

Re: Coincident constraint not working as expected

ajehresmann — Fri, 15 Apr 2022 01:18:03 GMT

Thanks again @j.palmeL29YX for all your very thorough help I really appreciate it. I think I just need to understand exactly how all the geometric constraints work and how I can use them better so thanks for the explanations.