Repairing "Broken" Fillets

StephenG

It is no surprise (quite common) for downstream fillets to break because the topology of the model upstream has changed; edges and faces the fillet references have "disappeared" or changed in a way that Onshape cannot adjust to.



Onshape is not very good and guessing how to remap to new edges/faces. At this time I do not think it even tries, but I can live with that.

But what I find hard to live with is the lack of a visual clue that points to where in the model the failed fillet is located. For the person who did not create (or forgot how) the original model/fillet was created there is little information as to where the fillet operation was applied.

What I would like to see is a "ghost image" of the original edges and/or faces (in red color) that were selected superimposed on the model. This will tell me exactly where and the nature of the topology change that will have to be accommodated to repair the fillet.

Anybody with a better idea?

NeilCooke

There's no way to guess an edge unless tangent is selected (better to fail than guess and get it wrong). The SolidWorks style dashed red edge is useful, but in Onshape you can compare your model to a previous version to see where the differences are. 

StephenG

Argh.... I can't believe you suggested using version compare. At least you didn't suggest that I could write a FeatureScript

The situation that precipitated this discussion post was probably a worst case scenario. Opening the failed Fillet feature form for editing...

gave no indication (with the exception of its radius value and the fact the "Tangent propagation" was checked) where the failed fillet was in the part, or even what part in the Part Studio it is associated to. (I have since discovered that depressing the "Final" button can be used to identify the part; which was was very helpful in my situation.)

I am not sure why the "Entities to fillet" list is empty. I has been my experience the lists contains the names of the original entities that were selected for filleting.

Consider the following example:
 block on block with interfacing edges filleted.

Design change: Top block changed to be a cylinder.


Of course the fillet is going to fail because the 4 edges originally selected no longer exist.

Opening the fillet feature for editing records...


the 4 edges selected for editing, but there is no indication as to which one(s) might be the problem. Problem entity entries are normally color coded red, but often the red color coding is misleading. Why all of them are not color coded red is somewhat of a mystery. It appears Onshape has no problem ignoring entities that no longer exist. For something to be colored red the entry must still exist and the fillet failed to generate with that entity. IMHO missing entities should also be colored red with the text "(Missing)" appended to the entry. 

Onshape's ability to ignore missing entities can make things confusing to next person that edits the fillet. The failed fillet was "corrected" by adding the new interfacing edge of the cylinder to the fillet. Now there are 5 entities in the entity section list for what should be a simple 1 edge fillet. 

The "power" of any modeling feature/operation is NOT in its ability to create geometry, BUT with the easy and robustness in which existing geometry can be modified (iterative design).

 <hyperbole>An end user should never be put into situations where it is easier to delete and recreate something because it too difficult modify/fix. </hyperbole>

I will let other Onshape users speak to the need to making fillet repair a little easier to effect.

NeilCooke

You are right, the edges in the list should really be highlighted in red, but what you will see is that the extrude that the missing edges belong to is highlighted both in the graphics and the feature tree so that should give you some indication as to where the issue lies. Then removing one edge removes them all. The original feature definition (radius) is maintained so you have not lost the fillet itself, just the edges that no longer exist.

By the way, using the compare tool, you don't need to have made a version, simply open the Versions and History flyout, select an history entry you know was good and select compare.

StephenG

I assumed the compare tool required at least one version state in order to use. Thanks for educating me that it can be employed against any two points in a part's history. I will experiment with compare to see how much it would have help me out in the situation I encountered. My 1st attempt to use it (several weeks ago) left me disappointed because I wanted to see/compare two sketches to understand the differences at the sketch level; the compare tool only works at the surface level.

In my failed fillet there was nothing in the "Entities to fillet" list when it failed; not sure how that happened so there was nothing to point back to in the Features list. I think I was incorrect about using the "Final" button to identify which part it belonged to. When I pushed the Final button it caused a part that was hidden to appear. I just assumed Onshape was showing me the "part" scope for the fillet. I am not so sure what I saw was accurate. 

I also noticed that removing one entry in a failed fillet "Entities to fillet" list removed them all. Hopefully it only removes just missing, or the problematic entries. This goes goes back to the point I made about having to start over when the feature's design is lacking with respect to being able to make simple modifications/fixes; image if dozens of sharp cornered edges had to be manually re-selected just because only one of edge went missing and had to be removed, or remapped to a new/different edge?