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Identifying and Removing Constraints

Message 1 of 7
1714 Views, 6 Replies

Identifying and Removing Constraints

It seems anytime I design anything, arbitrary constraints descend on the drawing without my advice or consent. worse yet is that I can't seem to even see them to remove them. When I go to edit drawings by changing dimensions, I always wind up bumping into these invisible constraints and am given cryptic error messages that don't lead me to finding and removing the interference. Can anyone please help ? Sample drawing attached.

Message 2 of 7
in reply to: cmoher34YL9W

What is not working?


Seems to be nothing amiss, no User Parameters - until you outline the change you want, and we can follow along?

Simple part like this, should have fully defined sketches.

Compare mine to yours, and change any dimension now it will not break.



5 more dimensions, some more constraints to make it work, mirror what suits is less work.....


Might help...

Message 3 of 7
in reply to: davebYYPCU

Sorry I got bogged down with other pressing matters and now have to rely on a faulty memory of what the matter was. I thing generically though, my issues always come around to trying to change a dimension and being blocked, usually with a message that changing the dimension will over constrain the design or part. When I go to unshackle the dimension that is causing the error, I can't even find it. It's either not shown or would be the last I'd expect or can undo. I definitely could use a course on just constraints as they always seem to be a nuisance to me rather than a help. I clearly haven't realized their usefulness yet.

Message 4 of 7
in reply to: cmoher34YL9W

A note that this video about how to momentarily disable automatically-generated constraints in sketches might be at least a partial answer to your original question.  Or, if you just like to read a sentence as opposed to watching a video: hold command on mac or CTRL on pc while sketching to draw an unconstrained path.

Message 5 of 7
in reply to: intelinc

That video makes no mention of his underlying preference setting, I have not needed the video’s technique, because as you sketch the constraints about to be inflicted are visible at the time, you decide to accept or alter as you go.


Fully define as you go, is the best recommendation I have received.


Might help....

Message 6 of 7
in reply to: davebYYPCU

While you might have no need for this particular feature, that doesn't render it without potential value for others. It can be challenging to track what constraints are being generated where, particularly in more complex or visually-dense sketches. Being able to ensure no extraneous constraints are generated with a single key can be helpful in these instances. My intent wasn't to contradict your answer (which I thank you for BTW), but just to add some additional info for others who, like me,  came across this posting looking for answers to a similar question.

Message 7 of 7
in reply to: cmoher34YL9W

When I first started using Fusion I drew lines on sketches in a way that would allow Fusion to automatically constrain the lines.  Seemed like a good idea at the time. The problem with that is Fusion would auto-constrain lines to things that were bad choices and that I would have not constrained the line to.  So you often get for example, a line that is made perpendicular to some construction line that it crossed, rather than it being parallel to the line it extended from.  The result was that later on, especially if I rotated something, the sketch and subsequent parts would go berzerk and I would have a broken and very hard thing to fix.  Worse, you might not discover the bad constraining until you got the dreaded failed to compute error, which can be very hard to resolve.


I found that the best way to get constraints right and as intended is to not let Fusion auto-constrain for you and pay very close attention to it attempting to auto-constrain as you draw the line.  You can prevent Fusion auto-constraining by deliberately initially drawing lines very crookedly and sometimes un-attached to anything else - so that they begin as blue or orange.  Then you manually constrain the line, making it black.  It takes more time up front but I feel pays off in the end especially if sketches get more complex.  Also make sure that as much as possible of your sketch goes black (constrained) as you go.  If you go a long way with lot of blue and orange lines and attempt to constrain it all later, you can sometimes fail to see little flaws that make the whole thing hard to constrain, or over-constrained when you want to add a dimension.

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