Hi all,

What are the known cause of failing fillets ? I often have to rebuild an object from scratch using a different method to get them to work

Hi Iwan, well there are many different things.

One thing is if you have surfaces that are nearly tangent with one another but not quite, like a crease of 4 or 5 degrees or so. Things tend to work better when pieces that are nearly tangent are built to be more exactly tangent.

Little tiny edges will cause problems, if you have a boolean that has cut something and the pieces were off alignment by a bit, that can create little tiny edges.

Surfaces that have a lot of sharp little wiggles in them will cause problems.

Surfaces that fold back over themselves or intersect themselves will cause problems.

If you have an example of something in particular, please post it and I can try to give you some advice that is more specific to that situation.

- Michael

Hi Michael,

Well, no special case in fact. I often have to try different shape blend method or play with value to get it to work (like 1.51 instead of 1.5), sometimes I need to rebuild the object, sometime I need to step back before another fillet for the present one to work etc. Also often on "complex" objects with small fillet, the trim is inverted and I get my fillet only and the rest of the object is gone (until I hit cancel of course !)

Hi Iwan, well there is probably no single cause that is happening to every one of these cases that you're describing.

It may be any variety of the reasons I mentioned above, or possibly others.

It is hard for me to give very specific advice without seeing any example models.

Filleting is generally a difficult area of calculation though, so it is not at all surprising to me that you will run into problems on more complex areas, especially when you have many edges coming together at one point.

If you need to do a lot of filleting of more complex models, you might want to look into one of the more expensive solid modelers like SolidWorks, Pro/E, etc... - they have invested a lot more time in their filleters so they are able to handle more complex cases than MoI.

Another thing you can do is to switch to surface modeling if you have a difficult fillet you need to solve. This involves using Edit / Separate to break your model up into individual surfaces, and then when you select 2 individual surfaces and do a fillet you will get a different style of fillet. This style does not try to hug directly along the edges and fix up corners where things meet up so it tends to be less prone to failing than the edge based fillets. You can often create a fillet surface with this method where the edge based one will fail to calculate. But then you do have to handle trimming things and trying to patch up corners manually.

The next time you run into a fillet issue if you post the model file here I can try to give you some better details.

Unfortunately filleting bugs are usually pretty difficult for me to solve myself, I rely on a geometry library to calculate these. I'm dependent on the people who make the library to fix filleting problems and make it more robust. They should be able to make progress in this area but it will be kind of a step by step thing.

- Michael

thank you Michael,

I solved most of my fillet problems by rebuilding surface with better shapes and careful booleans

added to the Special thread Gallery :)

hehe thanks Pilou but that's not finished :)

No problem people will can scrolling for see the next ;)