Dimension or constraint bug?

[ericschimel]

Alright everyone, I've been at this for hours and I can't seem to figure out the problem. I'm nearing the end of building this bench in 360 and I discovered that there's a bug when I try and change the "width" on the Modify Parameters.

As you can see, my "Bottom Plate" width isn't changing it's size when I punch in a new "Width" parameter. I cannot figure out where I went wrong, or if I'm seeing a bug. I'd really like to learn to fix it. I did try the "blow the sketch up and start over" method but it broke so many joints down the timeline it wasn't worth the time. If someone could take a peak at this and let me know where I've failed I would greatly appreciate it. Hopefully I'm missing something obvious.

http://a360.co/1MNVi0j

[jeff_strater]

yes, that seems to be a bug.  All it should need is a colinear constraint between the vertical outline line and the projected Corner geometry:

The first time you add this, it works fine.  However, on changing the width parameter, the sketch does not update correctly

This may be related to another bug I've seen, that we have a fix for locally.  I'll check to see whether this is the case for this model.

Jeff Strater (Fusion development)

[ericschimel]

That's fantastic news. I thought I was screwing something up.

I really appreciate you checking it out. When this bug is corrected, will my model start working again or will I have to do something to it?

[jeff_strater · Accepted solution]

It turns out that the problem is a bit more subtle than I originally thought.  Our sketch experts looked at your design, and found that there is an invisible dimension that is really causing the problem.  It is between the right-hand vertical construction line and the right side of the larger rectangle:

We have no idea how this dimension got created, or why it is not visible.  If you have any info on that, it would be greatly appreciated.

So, you can fix the design by simply deleting that vertical construction line.  Everything works fine then.  You can re-add the line if you want, and it still seems OK.  Here's a screencast:

Now, the larger question is:  How were you (or I, for that matter) supposed to know this?  I have no answer, unfortunately.  We'd really like to know how this happened, so we can prevent it.

Thanks,

Jeff 

[burnandreturn]

I would be interested in how you found the invisible dimension?

[ericschimel]

Ok, I think I might have found another similar bug...

In this sketch I am trying to get the three slots to be evenely spaced. I drew a driven dimension at the top. The two side ones are that dimension divided by 4. The middle one, being in the middle needs to be that dimension divided by 2. The way I've been creating these is to draw the dimension, click the one I'm referencing to (like d111) and it populates it, then I'll add the math (like "/2")

This is working for me all over the place except here. Try adjusting the "Width" parememeter and watch what happens. Then try to correct it by re-drawing the dimension. It won't work. In fact, when you hover over it, it shows the wrong dimension:

Did I screw up here or is this a bug? Thanks for all your help by the way.

http://a360.co/1MUscMU

[jeff_strater]

So, this is mostly working as it is supposed to.

The miscommunication here is that you cannot associatively reference a driven dimension in an equation.  Notice that the equations for your "spacing" dimensions are expressions such as "42.0 / 2":

This will always evaluate to 21.  It is not referencing another dimension.

How did this happen?  Well...  When we added the ability to click on a dimension when editing another dimension, we had a problem:  Because Fusion does not (yet) support associative references to driven dimension we had a spec question:  "what should we do if the user clicks on a driven dimension?".  And the answer was:  "just use the current value of the driven dimension".  Whether this is a good answer or not is arguable.  Fusion should probably at least issue a warning in this case.

The fix here is a more complex equation.  I created a user parameter which was "slots_width" and which had the value "Width - 2.0 * (d125 + d124)", and then changed those 3 dimensions to have the correct equation:  "slots_width/2.0", and "slots_width/4.0".  It works OK then.

The one thing that is definitely a bug is the hover text is wrong:

The value shown in the actual dimension (the green dimension) is correct, just the value you get in the "d133L 42.00 in" preview is wrong.  I'll report this so we can fix it.

Jeff