Making a Fillet that isn't round on a semi-organic shape

[mara_1 (Mara)]

Hi everyone!

I’m trying to fillet an edge, but I don’t want it to be round—more of an oval/elliptic shape. Ideally, it would look something like this:

The sides of the model are 30mm thick, and I’d like the fillet profile to start at half the thickness of the profile (15mm) and smooth onto the surface over 100mm.

I’ve tried to ask for advice from ChatGPT in order not to bother the forum. It suggests drawing the elliptical profile and then doing Sweep2, but doesn’t really explain how, concretely. I don’t understand what the two rails are supposed to be…

And then it tells me to Trim and rejoin to the base surface, but as far as I’ve realized, I can’t really use trim in polysurfaces.

A bit about my skill level:

I’m an intermediate user of Rhino 8 on Mac, and I would prefer if the solutions didn’t involve Grasshopper or SubD. Ideally, I’d like to solve this using Sweeps and Lofts, if possible.

Here’s the model:

Here are the edges I want to fillet, highlighted in green:

And here is the file:

test_model.3dm (15.4 MB)

Thanks!

[davidcockey]

@mara_1

I’d like to solve this using Sweeps and Lofts, if possible.

Revised

Create a curve with the fillet shape you want. Or wait to create the curve.

Decide what “rule” to use for the offsets of the edges of the fillet from the initial edge. Possibilities include:

• Simplest would be two different but constant offsets. For that you can use OffsetCrvOnSrf to create curves for the fillet edges.
• Create two pipes of different diameter about the intial edge, intersect the pipes with the intial surface, and select the curves to be used as the fillet edges.
• FilletEdge with two different radius and Trim not checked. Use the edges of the resulting fillets as the new fillet edge curves.

Trim the original surface with the new fillet edge curves.

Set the Cplane as normal to a fillet edge for this. Pick a location where the Cplane can be normal to both fillet edges. Position the previously created fillet shape curve, or create the fillet shape curve. Match the fillet shape curve to the adjacent surfaces as desired.

Sweep2 with the trimmed edges as the rails, and the fillet shape curve as the section. Set Edge continuity in Sweep2 as desired. Rebuild rails may be needed to minimize skewing of the section. Slashes can be used to minimize skewing of the sections.

[martinsiegrist]

I’d start by rebuilding the object.

The way it is built now is problematic for further filleting.

In my opinion, these two surfaces would be a good starting point

For easier modeling, I’d place the object closer to the origin so we can use at least the Y axis for mirroring if necessary.

A simple offset creates this corner situation which I don’t find ideal:

Instead, I would use the front curve of the seating surface to trim the object:

Trimmed with two pipes:

BlendSrf can be used to create something like this:

test_model.3dm (13.0 MB)

[theoutside (Kyle Houchens)]

how to say this politely and respectfully… this file is an unholy mess.

this is a very very simple shape and you have made the most unnecessarily complicated surfaces to create it.

stop here, go back to the basics and get your curves built correctly, your topology straightened out and your main surfaces simplified and corrected.

watch this modeling video series That Sky did.
It’ll change your modeling forever for the better. I’ve been a pro modeler for 30+ years and I still go back and watch it from time to time, it’s that good.

the time you invest in watching this will pay off huge in helping you avoid pitfalls that you are facing in this file.

https://youtube.com/playlist?list=PLABJCJR46itOX8XT3bd2dh590McA94W7k&feature=shared

[mara_1 (Mara)]

I… don’t comprehend the process you used here at all! Maybe saying I am an intermediate user isn’t quite right… finding more and more how much of a beginner I still am. Having been using the program for about a year at this point, but this is the most complex surface I’ve modeled.
Could you explain the steps you took here? Thank you for your help!

Also, I really need to keep the variable inner fillet on the inside curved part.

[mara_1 (Mara)]

Thanks for the tip! I know it’s quite the mess… trying to solve it as much as I can. I’ll watch the playlist.

[theoutside (Kyle Houchens)]

with your permission I’d be happy to make a short video on how to fix this as long as I can share it publicly once its done.

I see common issues like this all the time and it’d actually be a great case for a demo on how to make it better-

[mara_1 (Mara)]

Hi! Thanks for the offer and all the help, but I would prefer it not to be public, so I’ll have to decline.
However, the YouTube series you sent me has helped me a lot just in the three first episodes, so you have already been of great help!