Thanks Frenchy

I've got the new script working in my copy of V2 and fixed the model so no naked edges show but it still won't fillet all at once or larger than 0.5 if I do them one at time.

The other question is why does the model have to totally water tight for the fillet command to work properly ? Shouldn't it just fillet anyway, because in some instances you want open edges on you model but still need the fillet command to work .

Attached is my watertight version that I still can't fillet and figure out why it doesn't work.

Hi Kevin, just another illustration to add to the above.

If you zoom in on the top view, you can see that what looks like it should be a totally vertical cut is actually kind of misaligned:





That's a projected distance of about 0.04 units between those top and bottom edges.

Of course it would be nice if this would fillet anyway, but the fillet mechanism will tend to work a lot better when the pieces have greater alignment. It actually can be harder on it when things are set up like this when things are pretty close to being aligned but not quite, it tends to make stuff like slivery intersection results in the calculations.

- Michael

Hi Michael thanks for responding.

I'm sorry, I still don't get it ?

If my model as a slight taper on the face between the top and bottom edges (this was unintentional of course). Shouldn't the fillet command work on tapered faces just as well as vertical faces ?

Hi Kevin, it should work but it tends to be a much more difficult situation for the fillet code to process, particularly if the difference is very slight.

Generally a very small taper will cause problems, to avoid them it is best to have either no taper or one that is a bit larger than that instead of so slightly tapered.

Slight differences tend to cause things like really skinny tiny corner pieces, etc... Those throw a monkey wrench into the fillet mechanisms when the sliverly pieces get to be around the size of the fitting tolerance.

Already filleting like many operations has to work to an approximation or fitting tolerance, when major pieces like corners are also around the same distance as the fitting tolerance pieces tend to get munged together instead of clearly differentiated.

I certainly agree that it would be better for the filleter to handle all situations that you could possibly throw at it and never have any difficulties processing any kind of arrangement of objects.

Unfortunately it takes a really long time and a huge amount of effort to get fillet processing code to that level. MoI's filleter is not to that level yet, but you can get pretty good results with it if you help it out by avoiding some of the areas that it is weak in, such as slight taper and misalignments.


So it's just some good practical advice given MoI's limitations, does that make more sense?

- Michael

Michael

Thanks for the explaination. At least I know now some of the pitfalls of the fillet command so I've learned a lot from this thread.

I was kind of hoping this problem was something you could easily fix in the software (reason for my post) but its not sounding like it.

Hi Kevin, yeah unfortunately fillet problems tend to be very difficult to fix.

The whole calculation of a fillet has quite a few different pieces in it, it involves calculating offsets of surfaces, intersections of surfaces, extensions, construction of fillet surfaces along rail paths...

Any single one of those is actually a pretty complicated operation, and fillet has layers of many of these parts.

In your particular original case, it looks like the part that is breaking down is the calculation of the intersection of the fillet with the side surfaces for that middle piece. The steps that Burr shows above cause those side pieces to be replaced by plane primitives, those can get some special case assistance in intersection calculations that seems to help out in this case.

It is good to have examples of things that don't work right, but for filleting most of the time I will be gathering them up and sending them over to the people who make the geometry library that I'm using so that they can examine them and try to tune things up. That will tend to be a rather long and drawn out procedure though.

In some cases I may be able to do something about it sooner than that, like Pilou posted one recently that I was able to fix up right then actually. But that will tend to be rather rare with fillet problems however.

- Michael

No problem Michael

In a lot of cases I can work around the issue by sweeping a surface to create the same effect, its just more work thats all.

While both you and Burr and some of the skilled MoI users have found and suggested workarounds (thanks), I think it is beyond the average user to figure this out for themselves leading to frustration.

Hopefully this thead will help them when they have filleting woes.