Help designing an open to closed loft with no obvious planes

richard_kovanov

Hi there! I'm new to onshape, and especially new to surface modelling.

I've watched many videos on the topic and read some threads here, but I'm not managing to come up with a way to design an object like this (it's the top of an orthosis):

The complexity is that I can't find obvious "planes" I can use for cross-sections. What I tried was 3 ellipsis + guided loft like this:

Followed by some awkward planes where I drew some sketches to cut the faces with:

And then I can delete them and end up with something like:

This is not terrible, but it's more art than science (especially the way the sketch planes project to the faces), so I don't feel like I can really control how to cut those faces and merge the open area with the closed one. The curves on the real object are way smoother.

Any suggestions on better ways to try to design objects like this?

martin_kopplow

You are in a situation most find themselves in when starting surface modeling. It usually takes a lot of practise and then quite some helper geometry, if you need precise parameters. In this case, EG for the top end, you might want to try looking into the "projected curves" tool, that's the one that looks like a flying pancake: It will give you things like the upper curve all way around in 3D, and in a straightforward and controllable way, at that:

https://cad.onshape.com/documents/ca1999012c8f8157ad62d9c6/w/bfb4e68fbfd9f99849b5b14a/e/058fecc1d6e4413f61ef0e68?renderMode=0&uiState=68ba9cf4867a1f952b42115bThe model is simplified to save a bit time, but you get the idea. Note that curves in the projected sketch planes need to match, and the guide curves need to "pierce" the profile curves by conditions set. Play around with the model to see what happens when you change one thing at a time …

richard_kovanov

That's amazing! Thanks so much!