Hey, quick question. I have been working on the same drawing for quite some time and I recently noticed that some of my parts, which were fine for months, seem to be breaking. Attached is 2 of the parts and while you can see they are still considered solid, the faces in some places are either missing completely or severely distorted. Attempts to repair the parts by trimming off the affected areas cause unpredictable further problems. What is going on here? Since the parts are still considered solid does this even need to be fixed? How can I fix them without completely remaking the part?
Thanks in advance!
-Sean

Hi Sean ...
I don't really have anything to offer except to let you know that the solids are solids on my system.
cheers,
eric

Hi Sean, so faces looking like that usually means there's something wrong with the structure of the trim boundaries, something like edges or the uv part of edges criss crossing over each other or reversed in direction. These need to be repaired by separating out the broken face, and either building a new one and rejoining it, or doing an untrim and a retrim of it.

An object will read as solid just if it has no naked edges in it, meaning all edges are joined between 2 surfaces. It's unfortunately not very practical to do a more comprehensive analysis of an object because trying to find these types of boundary problems would involve a lot of calculation, and the object properties panel needs to be updated on every selection.

I'll see if I can tune those up for you. The process of doing low level repair operations like untrim and retrim is covered in this object repair tutorial if you want to know the details of how its done: http://moi3d.com/forum/index.php?webtag=MOI&msg=446.17

- Michael

Hi Sean, here's a repaired version of the smaller object. On this one the trimming boundaries were ok, the problem was that the underlying surface for that face was shifted some distance away from the trim boundaries. There's a bug in a geometry operation somewhere I think in filleting that does this rarely, I haven't been able to get a step-by-step example of how it happens which I'd need in order to get it fixed.

I'll see about the other piece next.

- Michael

Hi Sean, here's the other fixed up one attached. This one was a trimming boundary problem, somehow one of the edges in the model isn't there, probably another bug in some previous geometry operation but unfortunately I can't figure out where just by looking at the final result.

I fixed it by deleting the bad faces which were all around the missing edge, making new ones with the help of a line drawn in where the missing edge was at and then using Edit > Join to glue them back into a solid.

It's possible to repair an object with a couple of busted areas like this by using some "low level" surface operations like deleting faces or using Edit > Separate to detach them, then either doing an untrim/retrim of the damaged face or creating a new one and using Edit > Join to glue them back together. You don't need to remake the entire object this way.

Hope this helps! If you ever happen to catch this problem right when it happens please try to undo and save off the version of the object before it happens so I can try to repeat it over here. I'll need to "catch it in the act" in order to find out what was making the bad result and have a chance at fixing it up.

Thanks,
- Michael

Wow, thanks. I was just hoping for advice, I didn't think someone would fix the parts for me. If the missing face in the smaller part was caused by a random bug what about the distortion in the larger part? The bugs carry over into an stl file. I wonder what would happen if you tried to print them anyway.
Thanks again.

Hi Sean, no problem. If you tried to print them it would probably be rejected by the printer software that takes in the .stl file and generates slices.

The problem in the larger one is also likely to be caused by a bug somewhere but a different one than the other one. I can't really tell for sure exactly what went wrong though just by looking at the end result unfortunately.

- Michael