Why is this loft following a path so wierdly?

pavel_maňásek

I am new to onshape and CAD in general and I jumped straight into designing something pretty complex. I am trying to design a turbocharger that will get 3D printed and mounted to a small motor to spin it.

The impeller was surprisingly easy, the problem lies in the housing. I have made a big circle as a path, on the big circle there are two smaller circles of a different size and i tried to make a solid loft between them with the path specified as the big circle. The loft gets created, but instead of it being as simple as it could be, it tries to create a more complex shape that's skewed. I need a simple snail shape that will lay flat on the top plane and the pipe will gradually get thicker.

The second loft for the air output works just fine. Any other tips for the design would be appreciated.

The document: https://cad.onshape.com/documents/8fdce172d24427e586b26b1d/w/b18e9b4e8386b6080ee68228/e/d7eec2338951b01066cb754a

glen_dewsbury

The circle in sketch1 forms a closed loop when used as the guide curve. I trimmed back to the start and finish of the loft and this is the result.
https://cad.onshape.com/documents/c62e89ddc8a796ca30b84465/w/283e65a06e20bb38aea8c5b2/e/46ff3acb4f00dbcd19f2a805

martin_kopplow

You need more support geometry.

https://cad.onshape.com/documents/871aab8070ee453d0ab71288/w/44dde30ac4d4ad529dfce2de/e/39694a5e6fc447904cd6125e?renderMode=0&uiState=662d5f8feefd7e206d20a8d0

This support geometry could be more profiles or more guides or both, and well defined start and end conditions.

glen_dewsbury

The circle in sketch1 forms a closed loop when used as the guide curve. I trimmed back to the start and finish of the loft and this is the result.
https://cad.onshape.com/documents/c62e89ddc8a796ca30b84465/w/283e65a06e20bb38aea8c5b2/e/46ff3acb4f00dbcd19f2a805

rick_randall

Pavel, the way Onshape interprets lofts is a bit of a mystery, it seams to pick the easiest mathematical solution first - and is rarely the solution you want.

You just have to understand how guides, and paths work ( I seem to get better results with guide curves on complex lofts, and paths on very simple lofts).

Sometimes it takes a little experimentation to make it work - and the more you use it, the easier it gets

HINT: make sure all guide curves are coincident with profiles.

Good luck