Bug with computed sketch dimensions

[Witsend3486]

Hello,

I just hit this in the past few days: Fusion wants me to delete a dimension before it will allow me to change that dimension.  It seems to relate to dimensions that involve a computation, even a simple one such 12/2.  I get the message "Failed to solve.  Please delete or modify one of the following constraints/dimensions: d63...".  Dimensions that are simple literal values (like 6) don't seem to have a problem; I can change them to 7 or whatever without a hitch.

When I take Fusion at its word, delete the dimension, and try to re-dimension the feature, Fusion then says "Adding this dimension will over-constrain the sketch.  Choose OK to create a Driven Dimension."

This is a link to a project with the problem.

What I've done...

1. I entered a copyright statement in the comments, posted it, and closed the comment window.  (This doesn't seem to be important.)
2. I loaded a bunch of user parameters from two files using a free app from the app store.  (I don't know if loading via the app is important.  The app seems to be ParameterIO.py version 1.2.0 by Wayne Brill).
3. I set looking into the +X axis as the front view (also probably not important).
4. I'm modeling a full-scale prototype that is to be scaled down later for a model.  I set a number of dimensions by 'upscaling' them from what I want them to be in the model to what they would be in the full-scale prototype.  Thus, I originally thought I wanted d63 to be 3/16ths of an inch in the model, so I divided it by D$Scale (the scale factor) to produce the full-scale size.
5. I did similar things as far as I got in the sketch.  A number of dimensions are upscaled in the user parameters -- for example, D$Brg_P_ID is defined as D$Brg_ID/D$Scale.
6. Other dimensions are simply calculated from literal values, usually things like dividing a diameter by 2 to produce a radius.
7. Things were going fine until I changed my mind and decided d63 ought to be 1/4 instead of 3/16ths.  When I clicked on the dimension, edited 0.1875 to be 0.25, and hit 'return' Fusion came back and said "Failed to solve.  Please delete or modify one of the following constraints/dimensions: d63..."
8. I also tried changing d65 (across the very top of the sketch) which is just a calculated dimension from literal values (49.125/2), but doesn't involve a user parameter, and got the same problem.  d59 (the left side of the sketch) is just a plain, literal number (6) and it doesn't seem to have a problem.

This seems to be a relatively new problem since I've done this within the past month or two without a problem of any kind.  In the most recent update, I seem to recall something about fixing the sketch engine (making it more robust or something) -- this sounds like a good place to look.

I've attached the Fusion 360 Diagnostic Log File.  I just got the most recent Fusion update bringing me to version 2.0.5044.  Windows 10 Home is on automatic updates so heaven only knows what Microsoft has me running.  I rebooted (but did not power down/up) yesterday morning hoping that would cure the problem, but it didn't.

I searched the forum but didn't find anything recent that looked similar; unfortunately, I'm not very good at searching forums.

Respectfully,

Bill

[Witsend3486]

Jeff,

Sorry I haven't been able to reply sooner, but I had a car tell me it was time to buy a new one today.  Tomorrow it's the stove....

Perhaps the magnitude of the dimensional change is the issue -- if so I'll learn to live with it since without the dimension, as I recall, the sketch drags just fine, but....

If you go back to the original, complex project I posted in the very first article, you'll notice that I wasn't trying for what I would regard as a dramatic dimensional change -- I just wanted to change d63 (far upper-right corner) from 0.1875/D$Scale to 0.25/D$Scale.  Yes, that would be a 33% increase, but it's only 1/16th of an inch difference and, to me, not dramatic in relation to the sketch as a whole.  Furthermore, d63 is dimensioning a straight line with right angle corners at both ends.  The right-hand end connects to a vertical shoulder that is just dangling loose at the other end (because it is a simple layout sketch without the seat for the spring saddle that rides on the top of the bearing box).  The left end goes into another vertical shoulder that is the outer wall of the relief groove and does have a circular arc with a tangent constraint on its other end.

Also as I noted in the initial post, d65 (across the very top of the sketch) also has the problem.  It is 49.125/2 (a symmetric dimension being converted to an offset from the line of symmetry), but if you try to change it to 50/2 (about a 1.7% increase), you still get the problem.

There are more user parameters involved in the project initially posted, but I can tell you that you can safely delete all the D$IBLS_x parameters as they are not used in this design at all -- they are just part of a standard environment I load just to have everything around.  Also, the D$Brg_P_x parameters that have been used were all used in the sketch subsequent to the d63 dimension being created; they were, however, in use at the time I tried to change d63 and first noticed the problem.

Finally, as you will note in the first post, taking Fusion at its word and deleting d63 then caused an over-constrained sketch message to come up when I subsequently tried to re-establish the dimension for the line.  That really doesn't make sense to me -- deleting a dimension constraint ought to reduce the state of constraint, not leave it the same.  If something else established subsequent to d63 is effectively making the d63 constraint redundant, there should have been an over-constraint message when that something else was set -- it shouldn't be hanging around to force d63 into a driven dimension.

Respectfully,

Bill

[jeff_strater]

@Witsend3486, thanks again for your patience here.  I got word from the solver team that the solver bug in the simple case has been identified and fixed.  Of course, it will be some time before the fix makes it into a Fusion update, but hopefully it will be relatively soon.

[Witsend3486]

Jeff,

Excellent.  Thank you.  I look forward to the update.  Fortunately, a recent review of my overall project has revealed many other objects that need to be modeled which will not require this bug fix, so I can easily afford to wait for the update.  My instinct tells me that this bug fix will cure the issues in the more complex problem of the original post.

Thank you again for your prompt attention to this matter.

Respectfully,

Bill

[TrippyLighting]

Your current design also does not require a bug fix if you would simply follow the advice provided to you by folks with more experience and simplify.