Arc/Tangent Dimension Flips When Underlying Geometry Changes

[gakoenig]

Hi Folks-

I have a sketch for some serrations placed on the outside of a round part. Those serrations are dimensioned off of the inside wall of an internal keyway, using an arc tangent dimension.

If I go futz with the underlying dimension of the keyway, that arc tangent dimension will often flip, causing my feature to be exactly how I need it *not* to be (i.e. the serrations interfere with the keyway by cutting through it). Any changes, and I need to manually go back in, nuke the dimension, and redo it to get Humpty Dumpty back together again.

Perhaps making this dimension a bit more robust would be ++good?

I can link/share the fusion file if anyone at ADSK needs it, but this can be readily reproduced.

[paul.clauss]

Hi @gakoenig

Thanks for posting! We do have some shown issues with arc/tangent flipping directions, but I would like to have a look at your file to ensure it is the same issue we've seen in the past. Most of the current issues relate to splines, but you seem to be seeing this problem with arcs. We do have some known issues here, but most of them should be resolved at this time.

I would like to have a look at the file so we can be sure we are reproducing the same issue - please share it with me using any of these techniques and let me know which sketch and what model changes are made to the keyway.

[gakoenig]

Sure- it isn't a rocket ship part (just a camera strap mount) so here ya go!

https://a360.co/2L7cRMi

Using a Master Modeling technique and breaking the parts out for individual machining later. The document sketch labeled Base defines the depth of the keyway. The sketch that controls the serrations around the base is in the Base component, Sketch 2.

Modify the Base sketch keyset depth either direction, and about half the time, the Arc Tangent dim in Sketch 2 flips.

[TrippyLighting]

While this is certainly annoying, the issue can also be fairly easily avoided.

Your Base sketch contains dimensions d89 and d5.

The sketch for the serrations includes d96

With a little bit of math you can dimension the position of the circle without having to use any projected sketch elements or relations to existing geometry:

In general this takes a little longer to set up, but generally is very hard to break.

[paul.clauss]

Hi @gakoenig

Thanks for posting! I was able to recreate the dimension flip in your file and have logged a new ticket for this issue (FUS-42653).

The workaround from @TrippyLighting gives a very robust sketch, and I also found that you can work around this by simply adding the tangent to tangent line as a sketch entity and then dimensioning it as well.

Hopefully this helps! We appreciate you bringing this to our attention.