Hi Warren, also one other note: The overall approach of NURBS modeling is very different than sub-d - you want to rely on 2D curves a lot more and also rely on booleans and cutting operations as a primary way of doing things. That can take a little while to sink in for people from a sub-d modeling background who are used to avoiding booleans at all costs. Instead with NURBS modeling often times building things as a simple extended piece and then using booleans should be the main approach.

Check out here for some links to discussions and general tips for people who are coming from a sub-d / poly modeling background:
http://moi3d.com/forum/index.php?webtag=MOI&msg=4865.2


The very different approach can take a bit of getting used to, but it's really because of these differences that MoI has different strengths than a sub-d modeling program and that's why it can be really useful as a companion.

- Michael

Dang, thanks for the awesome reply Michael! Wasn't expecting that much...

OK, I think I'm getting my head in the right place here but I have one last hurdle and I think it stems from my lack of understanding of the Fillet system. I need to Fillet certain edges so I get a nice edge for normal map baking. My problem is that I don't fully understand the rules as to what will and won't work. For example:



I can NOT get the highlighted edges to Fillet successfully and I feel that I would need them to in order to not have a hard edge there in my normal map bake in Modo. I either get a detached mesh containing the Fillet results, or Fillet ignores me, or it goes off into "Calculating..." land for what seems like forever.

Is there something I can do to this mesh to make Fillet happier?

File here : https://dl.dropboxusercontent.com/u/161473/MOI/FilletQuestion.3dm

Any help here would be great! I've run into a few problem areas like this and it feels like I'm missing a small piece of the puzzle that would let me rock and roll with this thing...

Also, I'm getting this when I try to Fillet the other side:



Is my mesh just broken? If so, how can I fix it? Or can I?

Hi Warren - MoI's filleter can have difficulty in several kinds of situations and that's one of them. The juncture area here makes this a more difficult thing to fillet than you might initially think:




It's able to generate fillet surfaces for that case but fails in figuring out how to intersect them with one another. Here I have used the raw fillets that were generated and manually trimmed them so you can see the kind of awkward hole area that needs to be filled. That's basically caused by all the surfaces surrounding that juncture being at different angles to one another:



The filleting engine in the geometry library that MoI uses is just not able to figure out how to process this kind of corner juncture very well, for cases like this you might try exporting your model to a different CAD program that uses the ACIS or Parasolid geometry kernels which have more sophisticated corner juncture processing in them, one program called ViaCAD is pretty inexpensive and can make a good companion program to be used for doing fillets which MoI has difficulty with.

- Michael

OK, thanks for the info. I downloaded the ViaCAD demo version and the interface is ... challenged, I guess is the way to put it. Every time I have to use it, I predict I will be irritated. :P

So is there a best practices for Filleting thread somewhere that I could read through or is it just an experience thing? The more I can stay in MoI, the better, so even if I have to change the way I build certain shapes it would be better than trying to juggle multiple apps.

Hi Warren,

> Is my mesh just broken? If so, how can I fix it? Or can I?

Your mesh is not broken there - what happened in that case is the filleting engine was not able to figure out how to form the corner juncture between the 2 generated fillet surfaces. When that happens just the generated surfaces will be returned so you might have a chance at using those pieces with some manual trimming in order to finish things up.

If you select your main object and hide it you'll be able to more easily see that those weird looking areas are actually 2 separate rounded surfaces that are separate from your main object. Those are pieces of what should be the fillet but it could not figure out how to get them connected up to one another because of their different widths.

The way fillets are constructed when 2 pairs of surfaces are at totally different angles to one another the fillets between them are then of different widths and positions and so they don't directly collide into one another totally evenly. So a "corner patch" has to be created at the juncture area between them, and that corner patch creation is a pretty complex thing to calculate.

- Michael

Actually, you know what? Maybe the problems I'm having are inherent to how I'm building things. I'm, by force of habit, building the larger shapes and then trying to fillet everything at the end that needs it. Is it better to fillet as I go along? Maybe that's less stress on the calculation engine?

Hi Warren,

> OK, thanks for the info. I downloaded the ViaCAD demo version and the interface is ... challenged,
> I guess is the way to put it. Every time I have to use it, I predict I will be irritated. :P

It's not so bad if you use it just for filleting, that just involves picking edges.

It's filleter is significantly better at handling more complex corner cases.


> So is there a best practices for Filleting thread somewhere that I could read through
> or is it just an experience thing?

There are so many different kinds of things there isn't really just one thread that covers every kind of geometry, it somewhat depends on the particular shapes that you are dealing with.

In the future I would like to try and license one of these other geometry libraries that has more sophisticated filleting to help out with this.

Some general things to avoid - it can help to have more simple edge topology with fewer edges coming together all at one single point. Also having things meet up at a very shallow angle can make things more difficult, it's usually best for shapes to be more distinctly sharp to one another or more fully smooth to one another.

Sometimes doing an initial larger radius fillet to smooth out one area of the model can then help to make the fillet generation easier in the original area - surfaces that are smooth to one another are easier to fillet because the fillet surfaces meet up directly and don't have as difficult of a corner juncture to have to be figured out.

Like for example in your case here, rounding off this edge here with a larger radius:





Will then make this area actually easier to fillet after that:






Another area to watch out for is fillets can easily fail if they just don't fit within the given area, especially when things are at sharp angles to one another fillets will want to eat away a lot of space and if they try to eat away an entire face or edge that will cause them to fail too.

Filleting is definitely a finicky area in MoI, it's a lot harder problem than what it might seem like to get different kinds of corner junctures handled well.

- Michael

Hi Warren,

> Actually, you know what? Maybe the problems I'm having are inherent to how I'm building things.
> I'm, by force of habit, building the larger shapes and then trying to fillet everything at the end
> that needs it. Is it better to fillet as I go along? Maybe that's less stress on the calculation engine?

Well, it sort of depends - ideally you would actually wait until the end like you have been doing, so that's not "wrong" to do that.

But if you have the possibility to reduce edge topology complexity (reduce the number of edges all colliding at any one single point), or smooth out a broad area of the model with a larger fillet or sometimes by just incorporating some rounded shapes into the initial profiles, it can be good to do that so that you avoid getting into difficult to handle fillets later on. That kind of takes some experience to sort of proactively plan for filleting in advance like that.

- Michael

SO GOOD, thank you! That worked. I'll try to keep that in mind in the future then. Now I want to dive back in and see what I can get away with. :P

Thanks a ton for your awesome replies! You're really going above and beyond here and I appreciate it.

Random question : Are the bolded lines important in terms of how easily one will be able to work with the mesh? Like, should I be trying to hide those behind other geometry when possible or anything like that? Or are they purely decorative?

Hi Warren, you're welcome!

> Random question : Are the bolded lines important in terms of how easily one will be able to work with
> the mesh? Like, should I be trying to hide those behind other geometry when possible or anything like
> that? Or are they purely decorative?

Well, they're not exactly decorative - they're a normal part of the NURBS geometry. The way NURBS objects work is you have a bunch of surfaces and those surfaces have "trimming boundaries" on them that define which areas of the surface are active and which part of the surface are holes or cut away portions.

When you do boolean operations the actual "underlying surfaces" stay the same and only new trimming boundaries are created that then trim away more parts of the surface area.

Those bolded lines are the edges of your model, the edges are what make up the trimming boundaries.

It's a pretty different geometry system than a polygon mesh object, with a polygon mesh your object is made up of all little facet elements and there isn't this same concept of a bigger "underlying surface" and "trimming boundaries".

So it's not like you necessarily want to get rid of those, it's normal for your objects to be made up of various trimmed surfaces.

- Michael

You can also use some external free monster for capricious fillets in Moi like Fusion 360! ;)
And come back to Moi! ;)
(you can renew after the end of each year! ;)
https://knowledge.autodesk.com/support/fusion-360/troubleshooting/caas/sfdcarticles/sfdcarticles/How-to-get-a-Fusion-360-Enthusiast-license.html

Why not use a Variable Fillet for keep the original "sharp edge" before the last Fillet? ;)
Of course here you must make that in 2 passes due the little angle of some edges as shown above posts!



Don't press Done after the first Fillet(s) here 25° before make the Variable Fillet(s) of 0° of the 2 points on the right of the yellow "curve line"!
You can make and erase any number of different Variable Fillet(s) on the same curve(s) first selected as long as you are not exit of the Fillet function!

Variable Fillets are a little tricky but with a little training that is very easy and powerful! :)



Here a general last Fillet of 5° for example!


And careful for the second Point of the Variable Fillet of the Back faces of your ob!ject!
Maybe a zoom must be made because you have very near closed points!!!
So the Variable Fillet (s) or normal Fillet will be not work on the bad point!