Misleading fully constrained sketches

[rokenbuzz]

I have fully constrained sketches throughout my large project and if I change a dimension early in my timeline some sketches will go bonkers. One example is a constraint in the fully constrained sketch that has a line's endpoint being coincident to a circle. Think of a rectangular tab on the outside of a circle. And after my single minor upstream dimension change on something far removed, the line's endpoint IS still coincident to the circle, but on the OTHER side of the circle. lol Like, true Fusion 360, you got me there! So the line starts outside the circle, and instead of being coincident the circle right a few mm from it, like I had it, it crosses the first circle line and goes all the way across to the other side of the circle. Again, this was a fully constrained sketch so.. ugh. And in other sketches I've seen lines remain 1 mm from another line, like I had constrained, but now it's on the OTHER side of the line! It's like some sketches shouldn't really be consider fully constrained if Fusion 360 considers a different realization as a possibility. I dunno, I've spent days trying to make my large timeline be tolerant of tiny mm changes that should only shift everything in one direction, and yet it goes bonkers somewhere along the way every time.
I can't share this project for intellectual property reasons, but if anyone understands what I'm going on about and has suggestions, I'm all eyes.

[Drewpan]

Hi,

The sketches may have been fully constrained when you created them but you have gone back in time and changed a

critical value that makes fusion totally recalculate from the change forward again. What dependencies might you have

broken when you changed the parameter? This is a common issue and is the risk that you take with complex sketches.

One of the Guru Mantras is to sketch with simple shapes and use the tools to create the model you want. The more

complex a sketch that a model is based on, the more likely something will break down the track. I have seen several

people on the forum recommend many simple sketches over a single complex one.

As you can see with this shape, there are many curves and angles. I originally drew the sketch and it took ages to

get it right because every time I dimensioned it and made a change it disintegrated. As you can see from my browser

I used seven sketches in the end to get it right. Didn't break once. Simple sketches and used the tools to model it.

It is probably too late to go back and fix what you have now but there are two ways you could go about it. The first

and probably easiest way is start again. I know that you are probably thinking I am crazy, but many have found that

starting again, knowing where they went wrong the first time, and having already solved most of the hard stuff, that

a redraw happens much faster the second time around so it isn't as time consuming as you may think.

The other way is to make the changes in the timeline that you need then go in and fix stuff along the timeline in the

order it happened. Sometimes simply opening an edit and simply hitting "ok" forces fusion to recalculate up to that

part in the time line again. This often clears the error and a whole bunch of stuff un-breaks further along the timeline.

Sorry I cannot help further.

Cheers

Andrew.

[g-andresen]

Hi,

Unfortunately, it is not possible to draw any conclusions about possible causes from your description.

Share a file with an example sketch from which you can recognize the situation.

günther

[rokenbuzz]

I appreciate your suggestions. My sketches are already quite small and simple in my opinion, like the one of the openings in the model you show. But maybe I can break the troubled ones up further. Thanks.
In the past I have started over, but I think I'd only do that if I had a realization of some bad technique I'd been using throughout, and am now smarter.
Thanks

[rokenbuzz]

For example, this:

becomes this:

The change Fusion 360 made still meets the requirements of the constraints.

The outer arc is still centered on the inner circle. The vertical line is still coincident with the arc.

It started fully constrained and ended fully constrained.

It's like I want to also communicate to Fusion 360 that the vertical line coincident with the arc must be below the circle.

I couldn't have added any further constraints on it, could I? Once it's fully constrained I don't think that's allowed.

So am I supposed to be communicating what I want more clearly using different constraints?

Hopefully there is an "ah ha!" moment coming for me.

Thanks for any help.

[davebYYPCU]

Only thing missing - changing which parameter caused it?

Seen / reported similar behaviour with arcs / or trimmed circles.

Might help….

[rokenbuzz]

Changing the distance of the circle from the horizontal line at the bottom. Both are projected in this sketch.
That change makes the vertical lines in this sketch longer, as the circle is now higher up from that bottom horizontal line.
Sorry, I know it's hard to help without me sharing my file.

[davebYYPCU]

I can reproduce that.  Is similar to other projection / arc / circle problems previously reported.

[g-andresen · Accepted solution]

Hi,

---

@rokenbuzz wrote:

Sorry, I know it's hard to help without me sharing my file.

---

1. Isolate (reproduce) the two sketches in a f3d.
2. Where does this point come from?

günther

[jscott6SWZG]

seems to me that the  solver has enough information to arrive at a solution, but not enough information to arrive at unique solution. (thats kinda obvi).

Also some constraints have more information than others,  for example colinear has mor information than parallel.

I would remove some constraints and replace them with other constraints... in  the example, i would start with constraining the length of the short line intersecting with the arc.

[TrippyLighting]

Don't trim the circle. It's not needed in Fusion. Obviously that only helps in this particular case.

In general, the sketch solver still has room to grow

[rokenbuzz]

OMG! Was that it?!!! I think it was!
That point is another component/file I have linked for the purpose of positioning.
And within that, and another linked component, I still had under-constrained sketches. I fixed those and my problems seem to have gone away!
I made those components many months ago before I was smarter and more diligent about fully constraining sketches, and it simply didn't occur to me to look into those when battling this issue.
After this struggle, I think the importance of fully constraining has now been drilled into me even more.
@g-andresen THANK YOU SO MUCH!! Thanks to everyone in this thread!