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Can't shell my part! Help or alternatives please!

triharderttrihardert Member Posts: 9 ✭✭
Hi all,

First post, so apologies if my lingo's not up to scratch...

I've made a couple of projects in OnShape, but my CAD experience is definitely very limited. I'm trying to create an aerodynamic cover that goes over the front brake on my time trial bike. I've managed to get the shape 'sculpted', but I can't seem to shell it from the back to make it hollow.

Here's the document: https://cad.onshape.com/documents/89f0ea34cd032ba022e66925/w/79a3a84419db778821ce6d03/e/6d1554fe05b0ac55698e021e

I've used shell to hollow out boxes on my other projects, but no luck here. Any thoughts much appreciated!

Many thanks,


Best Answer


  • bruce_williamsbruce_williams Member, Developers Posts: 787 PRO
    Hi @trihardert and welcome to the forum.  Lots of helpful people here - but being the weekend, kinda quiet.

    The most important thing you can do is simplify your design.  Especially the splines.  You want to stick with 2 or 3 point splines.  Here is one of the really good tutorials  @billy2 has posted on the forum.  

    Also limit the blending geometry.

    I am sure by Monday you will have lots of other feedback.  In meantime, I suggest searching the forum for tips on splines, surfaces, and lofts.  Really good tips on here...
  • triharderttrihardert Member Posts: 9 ✭✭
    Hi @bruce_williams,

    Thanks very much for your advice. I've tried to simplify my part (part 3 on the doc). It's currently based off two simple extruded sketches and the shell has worked. However, I'm now struggling to produce the airfoil shape of the upper section that the loft enabled previously.

    I've tried to fillet, but it tries to do the whole line of the shape. Likewise, I've tried to employ this technique: https://forum.onshape.com/discussion/2436/how-can-i-stop-a-fillet-from-going-too-far-along-a-part but again, it tries to apply it over the whole line.

    Is there a way to select a portion of the line to remove using sweep?

    Many thanks,

  • steve_shubinsteve_shubin Member Posts: 560 ✭✭✭

    If you look through the features list of the document below, maybe this will help you


  • larry_haweslarry_hawes Member Posts: 478 PRO
    VERY nice Steve, looking through others' eyes at Onshape challenges really opens mine to the possibilities. Simple, clean, effective, again very nice. Hope it helps the OP.
  • steve_shubinsteve_shubin Member Posts: 560 ✭✭✭

    Thanks Larry

    Yeah it would be good if it helps the OP. But sometimes you just never can tell what will work for somebody
  • triharderttrihardert Member Posts: 9 ✭✭
    Wow @steve_shubin! That is amazing. Thanks so much for taking the time to have a look at it. I love fiddling with OnShape when I have a puzzle to solve and it's like you just did a Rubix cube in a few turns!

    Using the rollback bar I can see exactly how you've gone about it and it's much more elegant and much simpler. It also uses different tools I hadn't yet discovered so thanks also for that.

  • steve_shubinsteve_shubin Member Posts: 560 ✭✭✭

    I’m happy to hear you liked it !

    I was telling someone the same thing that you basically said. I told the guy — some people get up in the morning and they have their crossword puzzles (or Rubiks cube). Now instead of the puzzle or the Rubiks cube, we see something in the forum, and we’re left with figuring out ‘just how exactly is the best way to go about doing this’. And I enjoy that like you and others also.

    And I couldn’t agree with you more Tom about the rollback bar. I see a document someone posted in the forum, and that rollback bar turns every document  into a lesson. A very very nice thing that Onshape has. I’ve learned a lot about Onshape by using that rollback bar and stepping through other people’s documents.

  • steve_shubinsteve_shubin Member Posts: 560 ✭✭✭

    I got it down to 11 steps within the Feature List

    I did a solid extrude with remove. By doing this, I eliminated the last two steps.

    The above link to the document has been revised. It now has the 11 step version 

  • steve_shubinsteve_shubin Member Posts: 560 ✭✭✭

    Take a look at Sketch 2 to see how it was done

  • triharderttrihardert Member Posts: 9 ✭✭
    Hey guys,

    I know it's an old one but thanks to @steve_shubin's advice, here's where my brake faring design ended up. Just sent it to print  :)


    See Faring V2 tab.

    I'm sure you'll wince at some of the methods employed but it was good fun!

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