I just have started working with NURBS and would like to get some advice how you guys fillet objects. I saw tutorials for Rhino where you would have manual workarounds for some difficult forms.

Is filleting in some cases then separate process that you do after modeling, and you just find out how to get exact fillets that you are looking for?

Filleting for example detailed plastic bottle is not a problem but then more complex models seems to be quite painful. I have been filleting some splines before making surface to save work afterwards.

Thanks,
Timo

Hi Timo, filleting is a pretty complex topic, and one of the things that makes it complex is that you may need different strategies in different kinds of situations.

So that situational nature makes things somewhat context dependent and it's a bit difficult to come up with just some simple "one size fits all" kind of rules that are always going to work in every case.

It can be easier to discuss it if you can give some example models that you'd like help with, that would help to give some context to things.

But I will see if I can give some of the most common tips here...


> Is filleting in some cases then separate process that you
> do after modeling, and you just find out how to get exact
> fillets that you are looking for?

Pretty often it comes in later during the modeling process because a lot of times NURBS models are made up of different modules that are booleaned together, and normally it's only after the pieces are booleaned together that you then do the fillets.

There is an exception to this, there is a kind of filleting called surface/surface filleting that builds a fillet surface just between 2 individual surfaces, that particular case does not need to be booleaned together first. But edge-based filleting where you select edges or faces to fillet will need to have the pieces booleaned together first.


> I have been filleting some splines before making surface
> to save work afterwards.

Yes, this can work but it only applies to certain kinds of situations where the result is sort of self contained instead of being made up of multiple booleaned-together pieces.

But if you are doing something like an extrude or revolve or sweep for example where all you want are some rounded edges on the resulting object, that can be a good situation where you can fillet the profile curves and then have rounded pieces get constructed from them (instead of filleting the edges of the resulting solid). But often times these are not very difficult situations for edge-based filleting to handle ok as well though.


One tip - edge-based filleting can be sensitive to having edges fragmented into multiple pieces instead of made up of long single edge segments. There is a Merge command that can be used to glue together edge segments that touch smoothlly into longer single edges, that can be useful in some circumstances:
http://moi3d.com/2.0/docs/moi_command_reference10.htm#merge

Another thing that can help for filleting in general is to make sure your original profile curves are cleanly constructed and don't have things like excess fragmentation in their segments or have areas where 2 segments are kind of close to being tangent to one another but are actually off by a like 5 degrees or something, that can happen if you're just kind of "eyeballing" that things are close to being smooth instead of using tools that guarantee tangency like tangent/tangent arc construction, blending, or filleting of the curves. It can be hard on the filleter to resolve intersections in areas where the fillet surfaces are colliding together in places where things are close to being tangent but not quite and are a few degrees off.

One tool that can help to clean up messy curve structures with too much segmentation is the Rebuild command:
http://moi3d.com/2.0/docs/moi_command_reference10.htm#rebuild

But in general it helps to make sure your initial profile curve structure is nice and clean before you even start to build surfaces from it, if there is any messy conditions in your initial curves that will tend to have a ripple effect and cause problems down the line as well. It takes a lot less time to fix these problems in the initial curve framework to start with rather than trying to fix the surfaces later on.


Also another thing that can produce fillet problem is if you have little tiny edge or surface fragments in your model. That can get caused by messy profile curves, but it can also be caused by a lack of precision when positioning 2 pieces together before you boolean them. You want to make sure to position things accurately using object snaps to make sure things are aligned properly before doing booleans. If things are a bit off when booleaning 2 pieces together you can end up with little fragmentary pieces instead of clean cuts. That's another thing to watch out for.

- Michael

Thanks for previous tips for filleting Michael, I have modeled espresso maker and all other parts went well, with this top piece there is some many crossing edges that I could use some advices.
Middle section is made with loft from hexagon pieces and then booleaned front and back parts with it.
I checked all the intersections and they should be clean.

Thanks,
Timo

Hi Timo, what fillet radius are you trying to use?

You'll be limited to a pretty small radius value because there is not much room in the model in this area here:





You can't try to use a fillet radius bigger than what will fit within that smallest area of your model.

Over here doing a fillet of up to about 0.03 units seems to work:



You can't go much higher than that while trying to include that little area of the model because it would cause that little vertical edge to be completely consumed away and have the fillets from different separate edges that do not touch at a common end to collide into one another. The filleting engine cannot handle that kind of stuff.


I'm not sure if you're trying to fillet all edges here, or just the outer edges right around the hinge area where you've got some other edges already filleted. If you just want to do a larger fillet on the upper part of the hinge spot you may want to fillet that with a larger radius when it is a separate solid all on its own (and therefore does not have a small sized vertical edge in it) before booleaning it on to the lid.

- Michael

Its not problem with radius here really, but instead which edges to select.
So far I have worked fillets like this simple box example, where first set of edge fillets form rounded edge loop to fillet next. In this model there are too many intersections that I havent figured out where to start.
Could you show which edges did you select to get that example you have shown?

Thanks.
Timo

Hi timo - if you want to round off all edges then you don't actually need to select the edges individually, you can select the whole object and then run Fillet on it and that will fillet all sharp edges in the whole model.

Also you can select a face as the input to the Fillet command, which will cause all the edges that belong to that face to be targeted for filleting, sometimes that is an easier thing to grab than edges.

But I'm not sure if I understand - you wrote that the radius is not a problem? But that one area that I showed above is small in size, so that will limit the largest radius that will be possible - you won't be able to fillet with a radius that would cause that entire little piece to be completely eaten away.


> Could you show which edges did you select to get that example you have shown?

I just selected the whole object (just a single click on the object to select the full object, no sub-object selection at all) to target all edges, and filleted with a radius of 0.03 . That seems to be about the maximum value that will fit in that little area shown above.


> So far I have worked fillets like this simple box example, where first
> set of edge fillets form rounded edge loop to fillet next.

You would normally only really do them in different sets like this if you want to have different radius values on some different areas. Like for example if you wanted to have a result that looked like this:



If you want something like that where you've got different radius values on different edges, then do the fillets for the larger radius first (making some new smooth rounded edges like you were showing), and then do the smaller one on the other edges after that.

But usually if you want to have everything all filleted at the same radius then you would want to do them all at the same time, although if you've got different areas that do not touch each other you can do those separately if you want.

However, sometimes it can be easier to get things filleted by using different radius values in different areas and trying to build some smooth loops like you were talking about. That's because smooth loops are just easier for the filleter to process in general because a smooth loop will end up with all the fillet surface pieces connecting up to each other end-to-end directly instead of having "corner patch" type areas needing to be created to fill in more complex junctures where multiple fillets meet up.


It's not entirely clear to me which areas you want rounded in your lid - is there only one area that you wanted to be rounded or are you trying to round off every edge in the whole thing?

- Michael