Hi Tree, in fact I think the problem is that the fillets themselves do not even actually cross each other at all in that spot, it needs some kind of special logic to build a special connecting piece between the different fillets. The geometry engine that MoI uses just does not handle that particular kind of corner case right now.

Here's a bit more of an illustration - here I have manually constructed the fillets for that spot by breaking your object into individual surfaces and doing the fillet 2 surfaces at a time, which performs a surface/surface fillet which is different kind of calculation than an edge-based fillet:




You can see the fillets don't actually fully run into each other, they kind of touch just at a single point and pass by each other. Also see the attached 3DM file where you can zoom in and rotate around for a better look.

The ACIS modeling kernel knows how to handle this particular situation by trimming the fillets where they barely touch and putting in this connector piece here:


The part that is difficult there is that connector is done with special logic that is dedicated to just this particular corner configuration.

That's what makes fillets so difficult to calculate, many cases such as this one are more complex than just constructing the fillet surfaces themselves, it's handling the logic to connect the pieces together in different ways and handling a lot of different special cases.

It's a lot easier if you are filleting things that have a smooth outline in them rather than sharp or anti-tangent, etc.. type things, because smooth outlines will naturally make the fillet surfaces themselves touch each other and won't need complex corner connection logic.

- Michael

Another way to try and describe how the fillets do not "naturally" come together for this case is that the natural fillet pieces will be on opposite sides of that plane.

For example the fillet in one area wants to be like this:




But the fillet in a different area wants to be on the opposite side of the plane like this:




So those various fillet pieces kind of stay separated on opposite sides of that plane until the top or bottom spots where they would need to be connected up, that's what makes it a complex case.

- Michael

Hi Michael,

As always, thanks for the prompt and detailed reply. After a while working with MOI one gets the "feeling" where certain situations will be more difficult to fillet. This was/is one of them. I also noticed the difference where some edges where filleting out and others in and this combination of the 2 trying to come together was causing a problem. Oh I also did notice the little edge hiding in there btw. In most cases, for more complex objects I sometimes have to try a couple times to find the best solution to get a fillet to work. This one was a bit more difficult than usual, so I figured it was time to ask the guru.

Maybe the ACIS modelling kern could be something to consider for future versions of MOI. Although I'm not sure as to the availability of it or the degree to which others using MOI would also need something like it. I just love to fillet since using MOI. :)

Talking about viacad, I really have a bad experience so far, using the 30 days trials :

1) get a lot of trim error when importing MoI .3dm ... so I had so switch to .step, which seems not to be the best format either if I undestand it right.
2) get a lot of random crash, but always using the fillet tool ... complete freezing of the computer (-> reboot)
3) navigation sucks (but that's probably a matter of taste :P)
4) while indeed after all that problems I was able to resolve complex fillet scenario, the command itself is really slow, at a point that I prefer doing simple fillet in MoI, and only the complex one
with viacad.


It's quite hard to evaluate the support when testing , so does you guys have any positive experience with viacad ? aren't here any other ACIS based modeler around that doesn't cost an eye or so ?

Parasolid can do this but it will cost you an eye, an arm and a leg as well to get Solidworks or Catia.

so between 99$ for viacad (which don't seeems to like my hardware) and 30 billions for parasolid stuff there's nothing ... :S

So far my experience with ViaCAD is rather positive. It definitely doesn't crash on me. It doesn't run
on Win7 though, at least on my computer. In case I want to edit some Moi models with ViaCad , I export
as "step", "sat" should work ok too.

You might also want to check out Alibre, they have a $99 version, but I'm not sure right now about import/
export capabilities.

Hi PaQ,

Please take a closer look: http://www.t-flex.com/
~ $ 2000 and really great!

You may also take a look at Spaceclaim, its ACIS based and works copy/paste from Moi.
Spaceclaim Style doesn't really cost a fortune.

Hi PaQ, try using SAT format for going into ViaCAD.

SAT is actually the native format of the ACIS kernel, and possibly when importing this format they will avoid trying to mess around with (or "heal" as they call it) the data very much and just suck it in more directly.


> aren't here any other ACIS based modeler around that
> doesn't cost an eye or so ?

It's a pretty new thing to have any ACIS based modelers less than $1000.

The other inexpensive one out there is Alibre , they have a "personal edition" version for $99: http://www.alibre.com/products/hobby/

- Michael

Hi Tree, also one note on that little edge - you can get rid of it by using the Merge command which will combine it with its longer neighbor to make one long edge instead:

http://moi3d.com/2.0/docs/moi_command_reference10.htm#merge

- Michael

Hi Tree,

> Maybe the ACIS modelling kern could be something to
> consider for future versions of MOI.

Yeah, that is something I'm considering. But unfortunately the ACIS kernel is significantly more expensive and also has a lot more complex royalty based licensing than any other libraries that I currently use with MoI.

Another thing that kind of makes it complex is that it is not quite an entirely 100% "black and white" thing, there are actually some cases that MoI's geometry kernel will fillet that the ACIS one does not handle, although these are in the category of a large fillet radius going around a too-tight bend. I've attached an example, you can fillet this in MoI with a radius of 2 but it won't work in ViaCAD with a radius that large, that's because MoI's geometry kernel can sometimes slice out some areas of the fillet that would otherwise be self-intersecting:




But the ACIS kernel handles way more kinds of corner conditions where fillets need to come together.

- Michael

Hello,

SCE will perform that sort of inside corner fillet no problem, but it will not fillet that solid that MG indicated past 2. In fact there are instances where MoI will fillet where SCE will have trouble. The two applications are a pretty powerful pair.

Sorry : what is SCE ?

SCE = SpaceClaim Engineer http://spaceclaim.com

ok! Thx!

Hello everyone.
I'm not currently an MoI user because it doesn't have some of the features I need, but I have used it and really appreciate the care that's put into its development. I am however, a ViaCAD Pro user and that's the reason I'm replying to this thread. I just wanted to point out that the shape posted by Michael, can be blended in ViaCAD if you use the right option. It worked OK for me with a blend radius of up to 2.4 before giving an error message. To do it successfully you need to use the Variable Blend tool and select the Fixed Width option within that tool. I'm including the SAT file I made, for your scrutiny.

All the best.
Martin.

Hi Martin, that's definitely an interesting alternative. But the example you posted is actually kind of lumpy and not so great in that area, the surface has kind of gotten bunched together.

Here I've turned on the metallic lighting in MoI and examined your model. Notice these darker bands, which are actually little lumps in the fillet surface:






Compare that to this result created in MoI with radius = 3:






So not only does MoI allow you to go to a higher radius that ViaCAD is not able to reach, but also the surface generated for this particular case seems to be higher quality as well.

That's just this particular case though, there are quite a lot more cases where ViaCAD handles filleting better than MoI does, but not completely 100% of the time as this example shows.


- Michael

Hi Michael.
That's interesting. ViaCAD won't let me do a radius larger than 2.4 - it throws an error if I try 2.5. As for the surface quality, I must say it does seem OK within ViaCAD Pro. I've included a couple of screen shots of the shape with the Surface Analysis -> Environment Map applied to it. Do you think what you're seeing is something to do with exporting it as a SAT file?

Martin.

Hi Martin,

> Do you think what you're seeing is something to do with
> exporting it as a SAT file?

No, most likely it's just that the analysis display in ViaCAD is just not detailed enough to pick up on the small sized little bumps.

I've seen similar problems in other CAD programs as well - remember that the shaded display is actually generated by creating a polygon mesh approximation of the true surface. If too few polygons are created they can actually miss little ripples and you just don't see the true surface quality.

One of the nice things about MoI's viewport display is that it puts a much denser set of display polygons up than you typically see, (including putting polygons along every surface knot line) so it is able to more accurately display problematic surfaces that other programs just kind of gloss over.


In ViaCAD if you set the object resolution to "super fine" from the default of "very fine", you can start to see the bumps a little bit more, here I've re-created your fillet in ViaCAD rather than importing it from your SAT file and you can start to see a bit of the lumps in these areas:



see the traces of those 2 vertical lines in there? Even at ViaCAD's "super fine" resolution there are actually still not enough polygons being generated to be able to see it properly though. But you can see it a bit easier if you move the view around with the highlights running through that area.


It's very unlikely that ViaCAD would produce bad SAT output, because SAT is the native format of the ACIS geometry kernel that ViaCAD uses.


- Michael