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Change sketch scale and pitch throughout swept curve

Question asked by Chris Lamb on Apr 11, 2017
Latest reply on Apr 19, 2017 by Chris Lamb

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Hello all,

I've had some issues with my design, I've made 2 pieces which will go next to one another in an assembly. My issue with both is that I have created a helical sweep on the inside which I've made using a shaped sketch. I've found an issue, but unsure how I can correct it / get the effect I desire:

The first issue I'm having, is that the sketch appears broken along the axis where it joins with the other part, which can be seen in the images below:

The other thing I'm trying to do is vary the size of the sketch scale and also the number of revolutions whilst traversing the intersection curve - so the areas where the shape of the wall changes I can have a different number of revolutions, similar to the thread pitch within the thread feature.

Any help would be really great - I'm pulling my hair out over this one!

Thanks,

Chris

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John Stoltzfus Apr 11, 2017 11:25 AM
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What shape is the helix profile?
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- Chris Lamb @ John Stoltzfus on Apr 11, 2017 1:05 PM
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  Hey John,
  
  The path for the sweep is an 3dsketch of the intersection curve from a surface sweep:
  
  The profile is made to match the profile which is coming from another part (which will be below this part) and is positioned on a plane which is positioned on the endpoint of, and normal to, the 3dsketch:
  
  Made to match the endpoint of this part (with the same profile coming up to it):
  
  I want the sweep and profile to match on both parts, but then on the upper part (part6-1) to be able to then vary the size of the profile whilst it follows the path, so it begins at scale 100% then it moves along and becomes 0.75% of it's original size when it reaches the end of the path.
  
  I hope this makes sense?
  
  Thanks, Chris
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Vladimir Urazhdin Apr 11, 2017 11:49 AM
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It looks like you need a smooth thread transition between two parts in assembly.
My advice:
Create a one multi-body part that represents sub assembly with thread and save each body as a separated part.
Multi-body part:
Part 1:
Part 2:
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- Chris Lamb @ Vladimir Urazhdin on Apr 11, 2017 1:10 PM
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  Hello Vladimir,
  
  Yes, that's great! Thanks. I thought that may be how I'd have to go about it - which is fine.
  
  What I'm interested in is, if I can do that but on the second part I can change pitch, or the number of spirals, within that part.
  
  I'd also like that the profile itself could change size - it would be the same profile design, but if I could change the scale, so at the beginning of the sweep on part1 it would be x size, but then when it ends the sweep on part1 it would be 75% of it's original size, having been scaled continually throughout the sweep. Then I'd create part2 which would start as the same profile but at 75% of the original size and decrease to 50% so by the end of part2 the profile would be the same shape, but would have decreased to half it's size from the beginning of the sweep on part1.
  
  I hope this makes sense?
  
  Thanks, Chris
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  - Vladimir Urazhdin @ Chris Lamb on Apr 11, 2017 1:35 PM
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    Hello Chris,
    Yes, you got the idea.
    In fact, the multi body part is "the master model" you can use to generate the perfectly fit assembly items.
    Good luck!
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    - Chris Lamb @ Vladimir Urazhdin on Apr 15, 2017 9:24 AM
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      Thank you Vladimir,
      
      I'm still unable to get this resolved. I have made the parts as one now and tried to create the swept boss using a single part, however, I'm getting multiple errors. I'm getting zero-thickness geometry which I believed to be because of the intersection curve changing to a much sharper gradient from point to point as the neck comes from the body:
      
      As you can see, I reduced the height of the intersection curve so it doesn't touch the shaded neck, but I'm still getting a zero-thickness geometry:
      
      When it projects shows the curve, it looks how I want it to look, but it won't let me make it without errors.
      
      I have attached the parts (1,2 and 1&2 combined) so it may be clearer to see.
      
      I appreciate any and all help!
      
      Thanks, Chris
      Attachments
      PA-90130-CON-STAT-INNER-P1&P2.SLDPRT.zip134.9 KB
      PA-90130-CON-STAT-INNER-P2.SLDPRT.zip392.5 KB
      PA-90130-CON-STAT-INNER-P1.SLDPRT.zip313.6 KB
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      - Chris Lamb @ Chris Lamb on Apr 15, 2017 9:26 AM
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        I did also try to moving Sketch4 so it was "inside" the wall, but the rebuild error remained - with a geometrical error instead of zero-thickness!
        
        Thanks, Chris
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      - Vladimir Urazhdin @ Chris Lamb on Apr 15, 2017 2:23 PM
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        Chris,
        The best way to handle this issue is to upload part. Me or somebody else in this community will help you.
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        Chris Lamb @ Vladimir Urazhdin on Apr 15, 2017 3:05 PM
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        Hey Vladimir,
        
        Thank you. Yes, I uploaded the part to in my previous reply as it seems not to want to work for me!
        
        Thank you again,
        Chris
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        Vladimir Urazhdin @ Chris Lamb on Apr 15, 2017 11:25 PM
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        In this model tangency between two segments of 3D sketch are mismatched:
        It leads to disjointed thread bodies.
        Tangency between two segments are mismatched because of no tangency between segments here:
        My advice: replace the spline curve (blue) with arcs & lines and add the tangent connection to all junction points.
        It will let you use just one 3D sketch to swipe full thread.
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        Chris Lamb @ Vladimir Urazhdin on Apr 19, 2017 8:05 PM
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        Thank you Vladimir,
        
        What you've said makes a lot of sense. I appreciate it!
        
        I tried altering/ tracing the spline but failed, so I have redrawn using lines and arcs from the start - I now have the revolve which is similar and close enough the I'm happy with that. Once I finally get it right, I can change the assembly part and remote it, which won't be too much of an issue. However, with the part I can't quite get a couple of things right:
        
        Again, the swept revolve looks good, but is giving me the same errors.
        
        The revolve is working fine but when I try to make it tangent it goes crazy, because it is trying to alter the offset part, but the offset part I can't make tangent either because it doesn't match up with the original sketch:
        
        I had to add those lines otherwise the revolve doesn't work because it's open. I can't delete them and make the points merged/ coincident / tangent - because the relations don't add up and it goes crazy and the lines are going crazy as above when I try to make the other part tangent. I'm unsure how to get around this? I've attached the part also.
        
        Thanks so much for your help so far, I appreciate it a lot!
        
        Thanks, Chris
        Attachments
        PA-90130-CON-DYN-INNER (EDIT).SLDPRT.zip149.7 KB
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Change sketch scale and pitch throughout swept curve

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