Hi guys

I know this has been asked before but could someone please point me in the right direction regarding a Fillet query.
I want to create a 1 or 2mm fillet on the top surface as shown, I have tried scaling the model up without success. Is it because the surfaces are too complex if so were would I need to simplify them?

Also I will need to shell the model and have tried and failed, I guess I will need to copy & scale down then booleon subtract?

Any help will be gratefully recieved.

Alexander

Hi Alexander,

Instead of using the edge to apply the blend use surface to surface blend, to do this separate your model into individual surfaces [Edit] > [Separate] pick the two surfaces then apply the blend, I managed to get up to 2.85mm rad, when satisfied join the surfaces back up again [Edit] > [Join] and the shell command will work.

Find the result attached.

Cheers

Hi Alexander, also one thing that would help for shapes like this is to build the top piece as an extruded piece which then gets trimmed, rather than trying to build a surface with rounded corners in it right from the start (like by sweeping it along side rails for example). So something that looks more like this:




For NURBS surfaces it tends to be better to have rounded corners done as a trimmed away portion rather than part of the surface itself, because having a single surface patch that itself has rounded corners kind of degrades the surface normal in that area.

It's also pretty easy to end up with a self-intersecting surface in the way you have currently done it, there is a kind of "tension" at the end of the surface, see this previous post for some illustrations on how this can easily end up self-intersecting:
http://moi3d.com/forum/index.php?webtag=MOI&msg=1127.4

Self-intersections or near self-intersections tend to be bad for filleting and shelling, it causes the surface normal to kind of spaz out in that area and flip around a bunch. Both filleting and shelling involve creating an offset surface a constant distance away from the original one, going along the surface normal so if the surface normal is going a bit crazy it can cause problems with these operations.

- Michael

Thanks Michael, I was just investigating building Alexander's model using the solid approach and was going to explain the same thing, I had nothing to do and I thought you would of been asleep but I see you sleep with one eye open :)

Cheers

WOW !

You guys are the best...
I'm a nurbs newbie having only really worked with solids in parametric modelling, I'm just used to selecting the line to radius.

Many thanks for the help & advice.

Alexander

Hi Alexander,

> I'm just used to selecting the line to radius.

So normally that is what you would do in MoI as well.

But that creates what is called an "edge based fillet", which creates the fillet by kind of tracking along those edges.

There is an alternate way you can do fillets in MoI which is called a "surface/surface fillet" - that method is enabled if you select 2 individual separate surfaces as the inputs to the Fillet command rather than selecting edges as the inputs.

The surface/surface fillet command is limited in some ways, like it doesn't know how to build fillets where multiple edges collide in to one another and need corner patches. But it works directly off of surfaces instead of edges and can sometimes construct a fillet in cases where the edge base filleter gets confused.

The edge-based filleter has to do some more complex kinds of calculations for the way it handles things and so it can get messed up more easily.

But the edge-based filleter tends to be more convenient so you'll usually want to try and use it first, but you can use the surface/surface filleting mechanism as a backup for cases where the edge-based one does not work.

If you had the top surface as an extruded piece that was trimmed rather than with those kind of single-surface-with-rounded-corners type thing then the edge based filleter would likely work fine on it.

- Michael

Michael

Understood, many thanks for the detailed explanation.

Regards
Alexander