Loft between two ring sketches?

creyc

I've got two sketches I'm trying to perform a loft between, both sketches contain two concentric circles, or 'rings' that change in diameter along the loft.

I'm unable to get the loft to solve, just by selecting the ring sections.  I'm aware I could do two simpler lofts and boolean subtract them from each other, but this is something I do quite often and wonder if there's a trick to achieving this type of loft in one step?

cody_armstrong

@creyc Unfortunately you cannot yet loft between nested contours.  As you mentioned, the only way to do this currently is with two different lofts.

cody_armstrong

@creyc Unfortunately you cannot yet loft between nested contours.  As you mentioned, the only way to do this currently is with two different lofts.

3dcad

Depending on your requirements for loft ends, you can try loft a surface and use thicken to create material.

creyc

3dcad said:

Depending on your requirements for loft ends, you can try loft a surface and use thicken to create material.

Another similar (opposite?) method could be lofting the outer circles then shelling the top and bottom.  Unfortunately my needs require the wall thickness to taper from top to bottom, so neither the thicken nor shell methods really helps me here.  Actually, adding a draft does get me close to the shape I want, but is not quite as straightforward as using a 2nd loft set to subtraction.

matthew_menard

Do you need to do this with a loft?  Could you do this as a revolve instead?  It looks like you could make the cross section with the variable wall thickness you want at the top and bottom and then just revolve it around the center. Something like this maybe?

https://cad.onshape.com/documents/4d3a3befc86f475c86e135ad/w/ea2bd8a23ebc4bdcbf2079cf/e/96897a511e8247c2bd85b663

(sorry if the link doesn't work, haven't tried sharing much yet.)

creyc

matthew_menard said:

Do you need to do this with a loft?  Could you do this as a revolve instead?  It looks like you could make the cross section with the variable wall thickness you want at the top and bottom and then just revolve it around the center. Something like this maybe?

https://cad.onshape.com/documents/4d3a3befc86f475c86e135ad/w/ea2bd8a23ebc4bdcbf2079cf/e/96897a511e8247c2bd85b663

(sorry if the link doesn't work, haven't tried sharing much yet.)

matthew, FYI the link does work.

And yes, revolves certainly work for this simple example, and probably would have made it easier to visualize the changing wall thickness.  Many ways to skin this cat!

Thanks

3dcad

Revolve is very powerful tool and in many cases it can replace at lot of hoops and loops to get the work done.
Thanks @matthew_menard for remainder.
 

andrew_troup

I would vote for Not permitting nested contours for lofts, because it seems to me that the minor gain in convenience for simple use cases would come at the cost of mind- and code-bending complexity for use cases involving guide curves or end tangency controls. (Let alone more advanced controls which Onshape does not yet provide)

This is another way of saying that the software is compelled to build the internal and external sheets as two separate operations, and at best it could only be rewritten to conceal this from us in a subset of use cases. Segregating those use cases would not be a trivial challenge, and the whole exercise would require development resource which I would rather see applied to things which are actual limitations.