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Lofting hollow faces

tom_augertom_auger Member Posts: 115 ✭✭
I must be blanking out, but I'm hoping a quick jog will get me going.

Trying to connect these two using loft. I can't loft a hollow solid it appears (inner loop), and, whilst I can create two surfaces (inner and outer), I don't know how to convert them to a (hollow) solid afterward. I know I can just do the outer and then thicken but I'd rather not. What am I missing?

Best Answer


  • romeograhamromeograham Member Posts: 636 PRO
    The Loft feature cannot make a loft when there are inner loops.
    You can create the Octagon and Circle features as solids first. Then do the loft, and then shell afterward. If you don't want the three parts to be combined into one, then make sure you have 'New' selected in the scope of the loft feature.

    Hope this helps!
  • tom_augertom_auger Member Posts: 115 ✭✭
    You can create the Octagon and Circle features as solids first.

    Hi Romeo - thanks for the advice! This is what I tried earlier, but I can't seem to make a solid out of these shapes, since they are just edges - I can make two surfaces but don't know how to combine them into a solid afterward, and the loft will not let me create a solid using the edges that I already have.

    I suppose I could drop some more sketch planes and use the existing edges to make my profiles, but that seems like a lot of extra steps. Am I missing something obvious here?


  • romeograhamromeograham Member Posts: 636 PRO
    Answer ✓
    Here is a very simple Part Studio that may help - I'm not sure if I've captured your design intent, but you can see some of the options required to make it work here: https://cad.onshape.com/documents/cb88cc98359cc555d3f37f08/w/e9d4e656351e1b7fc03bc2e5/e/2cf677c0dbeb958a080e9d36?renderMode=0&uiState=61bf89f55fd10b7f07d6acd6

    Note that you need to make sure that your first parts are solids (Extrude >Solid) and your Loft is set to "Add".

    Good luck!
  • tom_augertom_auger Member Posts: 115 ✭✭
    edited December 2021
    Thanks for the follow-up @romeograham - I can make your method work, though I'm not getting as nice results as you - take a look where the loft joins to the octagon. Even with the magnitude at 2 it's still not fully smooth. Any advice on how I can achieve the same results as you did?

    Further, the Thicken kept it as two distinct parts, and I'm unable to boolean them to boot!

  • S1monS1mon Member Posts: 2,101 PRO
    edited December 2021
    It looks like you're trying to loft the whole thing, instead of just creating the transition as a loft. This is why you had to crank up the magnitude to 2.0 and it's still not doing the same thing that @romeograham did.
  • tom_augertom_auger Member Posts: 115 ✭✭
    S1mon said:
    It looks like you're trying to loft the whole thing, instead of just creating the transition as a loft.

    Thanks for the input @S1mon - can you maybe elaborate a bit? I selected the face of the cylinder and the face of the octagon solids and lofted those two, nothing more - isn't that what you mean by the transition?
  • S1monS1mon Member Posts: 2,101 PRO
    Looking at in more carefully, I see that I confused the picks for the thicken with with loft. 

    I do see a few differences:
    1. @romeograham just had tangency conditions for both ends of the loft. You have curvature for one of them. Normally curvature is smoother, but there's something else going wrong here.
    2. It looks like you may be thickening to the outside, which is often less likely to give the best results on the outside, but again this isn't the issue.
    3. Shell is a much more robust way to get the wall thickness, since you only need to pick two surfaces to remove, instead of all the surfaces to thicken.
    4. It looks like you have created two parts instead of one. Perhaps your loft was only merged with one of the two extruded parts?
    It would be a lot easier to help with this if you shared a public document.

    I think I've recreated the mistake you made. It seems like you picked the wrong end of the octagonal extrusion to loft. If I pick the far end, and use curvature/magnitude 2, I can almost get the loft to line up where you want it, but it has the step, just like yours.

    What you want to do is loft the faces that you're trying to connect:

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