Hi niko, here are some steps to show you how this alternate "extended surface" technique can work.

I've attached the result 3DM model as niko_protrusion.3dm .


To start with, I projected your smaller outline curve on to the surface, and used Trim to hack off the ends about where they started to curve in:



Then I went to the other side of the surface (the "inside" part of it), and drew 2 lines in at the ends of those curves so those lines are going inward towards the center of the shape:



Then I used the Move command on each of those lines, picking the line's own endpoint as the base point, and the line's own midpoint as the target point, so the lines now had some spacing off of the surface. I also trimmed back a little more off of the surface curves as well:



Then I put in curve blends and joined those pieces together to make rails that start off hugging the surface but then curve inwards towards the center of the shape:



Now a sweep can be done to make a surface that looks like this:



Or as seen from the outside, it looks like this:



So notice there that the rounded "tip" shape is a result of the sweep being submerged as it passes through the outer surface, instead of trying to build a surface directly to that outline curve.

Now with these 2 surfaces you can select each of them and use Fillet to build a surface/surface fillet to make a smooth juncture between them, you can use the G2 blend option for the fillet shape if you want a that kind of blend-like result:



That's an alternate approach to this problem which builds an extended surface that then gets trimmed back by the fillet, rather than trying to build it directly to a curve layout that does not have a regular non-pinched quad type structure.

You give up some of the "direct drawing" control over the shape of the tip with this technique, you have to manipulate that tip shape kind of indirectly by controlling how fast the surface submerges through the main one. But you're going to actually have much more regular surface structures with this way and you also gain some simplicity with a smaller number of surfaces involved, like just one fillet/blend surface to bridge between the pieces rather than fragments.

Also you can adjust the radius of the fillet which is kind of like adjusting the spacing between the 2 offset profile curves that you were using.


I hope this alternate approach may be useful. Let me know if you try it and get stuck on something.

- Michael

I have to say again, this is the kind of stuff I feel needs to be in a Tips & Techniques section somewhere in the manual.

It's never about how each tool works - that's easy, it's about why, when and where to use each tool - I learn from these kinds of threads every time!

-Will

Hi Will, well this is a good example of a technique that is tied to a particular shape that someone is asking about.

Those kinds of tips that involve a particular model are are kind of easier to do when the person is able to present their particular shape that they are working with.

The manual isn't interactive like the forum is, so these kinds of tips just generally happen on the forum more than in pre-canned written material.

- Michael

Thanks Michael.

Yes I'm aware of this method and it works, but as my example shows it calls for situations where an adjustable fillet would be necessary (otherwise the filleting in this case is almost non existent).
Hopefully this is planned for V3 along with the continuity options for network and sweep commands.
I also have included the version where the fillet is done in Rhino using the adjustable fillet via add handles.

Hi niko, in the attached model I have your Rhino created one on the left, and a regular constant distance fillet one created in MoI on the right.

Here is what it looks like shaded, I guess it is hard for me to see much of a difference?



I do want to add a variable radius fillet into MoI though. I'm not exactly sure when that will happen yet.

- Michael

Michael
I don't know how you did it but my version of MOI cannot produce the fillet you just did.
How did you do it??????????

Hi niko, I untrimmed everything, and moved the small one a little tiny bit to the left (so it wasn't just barely grazing the edge of the main piece) and used surface/surface fillet.

- Michael

Hi niko, here is the file before filleting.

You don't need to try and trim and join the pieces beforehand for surface/surface fillet, just have the 2 surfaces as separate objects and select them and run Fillet.

- Michael

Wow thanks

I was under the impression that surfaces had to be joined and you then fillet the edge. that is much easier...

Which brings me to the next question


I guess the rules of filetting is a dark cloud to me.
How come I can't fillet a cube intersecting a sphere the same way you did the last two surfaces??
Sorry for being a dumbass man I just want to learn everything I can about MOI..

Hi niko, Michael did mention 'surface to surface', so if have a sphere intersecting a cube both are solids and that method of filleting won't work for that situation, but if you separate the cube into individual surfaces you can then use surface to surface filleting and then join everything back to a single solid body.
Usually in that situation you would Boolean union the solid bodies then apply the fillet using the intersecting edge, either way works.

Cheers
Danny

Hi niko,

> How come I can't fillet a cube intersecting a sphere the
> same way you did the last two surfaces??

Well, you could, but like Danny mentions you would need to break the cube up into individual surfaces.

That other kind of fillet is a surface modeling technique that builds a fillet between just 2 surfaces.

If something is made up of a lot of surfaces and also has sharp corners where those surfaces meet, then the regular edge-based filleting is usually better since the edge-based filleter handles creating multiple fillets surfaces and also deals (or tries to anyway) with trimming back fillets that collide into one another and putting in corner patches in those areas.

But if you are already working with surfaces, the surface/surface fillet can be handy, and also it is somewhat less complex than the edge-based one, so it can sometimes succeed in building you a fillet surface to work with where the edge-based one can't figure stuff out.

- Michael

Thanks guys