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Loft twist

rachel_hollisrachel_hollis Member Posts: 4
I'm using a book called Onshape tutorials. Chapter 8, exercise 1.

The base is a circle whilst the top has 4   3point arcs with 2 tangent lines too.  How do you loft this complex shape. I get arbitrary twists a curves going up.

R. H
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Best Answers

  • rachel_hollisrachel_hollis Member Posts: 4
    Answer ✓
    Thought I ought to pop on here and thank you both for the help, I've only had onshape a week and exercises like this are test. 
    https://cad.onshape.com/documents/5e52be110a7a6769ba152ace/w/99dba5b325a59dd1674e5970/e/5bde45beb53f725d0a391c4e

Answers

  • bruce_williamsbruce_williams Member, Developers Posts: 842 PRO
    @rachel_hollis

    Welcome to the forum! 

    You have a common issue, although I am not familiar with that specific lesson.  You will need to add geometry to the circle to use for 'Match vertices' in Loft command.  Anything which creates a vertex coincident with the circle including split the circle, add a point or line with coincident end point, etc.    

    A circle naturally has no vertex and the Loft command can find it ambiguous as to what to match.

    Lofts are tricky as they have many controls which may be added.  Refer to Loft 'Match Vertices' help here
    www.accuratepattern.com
  • rachel_hollisrachel_hollis Member Posts: 4
    Answer ✓
    Thought I ought to pop on here and thank you both for the help, I've only had onshape a week and exercises like this are test. 
    https://cad.onshape.com/documents/5e52be110a7a6769ba152ace/w/99dba5b325a59dd1674e5970/e/5bde45beb53f725d0a391c4e
  • rachel_hollisrachel_hollis Member Posts: 4
    Thank you.
  • bruce_williamsbruce_williams Member, Developers Posts: 842 PRO
    edited February 2020
    @rachel_hollis

    Good job - that is a challenging one for an intro. 

    A few tips:

    Your sketch 1 looks good; all black.  Sketch 2 is red due to being over-constrained.  I removed all but one of the 21.5 dimensions to fix that.  The arcs are tied to same center and have common end points so added dimensions cause error.   

    Also, I put in construction lines for Coincident constraint on the vertices of arcs.  That makes the sketch black (fully constrained) and puts the vertices where you probably want them so the corner blend is correct. 

    See copy with corrections here
    www.accuratepattern.com
  • rachel_hollisrachel_hollis Member Posts: 4
    Thank you for that Bruce, I wasn't overly worried but still tidies it up. The finished exercise is wonderful piece of work to do. here's the final item. :)

    https://cad.onshape.com/documents/5e52be110a7a6769ba152ace/w/99dba5b325a59dd1674e5970/e/5bde45beb53f725d0a391c4e
  • baffour_oseibaffour_osei Member Posts: 2 EDU
    I just figured this out. When you go from a large circle to a small circle using the loft tool, the loft maintains its shape; however, when you go from a small circle to a large circle, the loft twists. I don't know the reason, but it does
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