Rhino developable surface error-what's wrong

Discussion in 'Software' started by M.Ezell, Mar 13, 2011.

  1. M.Ezell
    Joined: Oct 2008
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    Location: Portland, OR

    M.Ezell Engineer, PE

    Hi All,

    I am building a plywood sailing canoe. I am also learning Rhino. I thought I would build a 3D model of the canoe from the plans and create tool path files for a local fabricator to cut out the pieces. Here is a half model. When I try to unroll the surfaces the shear plank unrolls, but with the bilge and bottom planks I get the message "There was an error unrolling that surface".

    I built the surfaces by drawing the chines with interpolate curves and create surface with 2 or 3 curves using the bounding splines. I only selected two curves per surface so I am pretty sure that they are developable. Can anyone out there tell what's wrong?

    Mark-
     

    Attached Files:

  2. Dean Smith

    Dean Smith Previous Member

    did you try the squish or smash commands
     
  3. M.Ezell
    Joined: Oct 2008
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    M.Ezell Engineer, PE

    "did you try the squish or smash commands"

    Hi Dean,

    Don't those commands change the shape? I thought that the flatten commands other then unroll stretched the shape. If they don't I'll definitely give that a try. Thanks!
     
  4. Dean Smith

    Dean Smith Previous Member

    nah they do not. Can you check the areas alongside say, maxsurf workshop
    well I THINK they do not, I,ll try some surfaces in both smash squish and unroll and come back to you
     
  5. DCockey
    Joined: Oct 2009
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    DCockey Senior Member

    If the surface won't unroll with the Unroll command then usually it is not developable. Squish or Smash uses internal stretching or compression to flatten surfaces with are not developable. That's how it is able to flatten them.
     
  6. Tad
    Joined: Mar 2002
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    Location: Flattop Islands

    Tad Boat Designer

    In my experience unroll only works if the surface is curved in only one direction and is absolutely flat in the other.........it's easy to inadvertently get a tiny bit of hollow in a surface that looks flat....then unroll won't work....
     
  7. DCockey
    Joined: Oct 2009
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    DCockey Senior Member

    Attached is a file with a redone hull surface (green) and the unrolled panels (light green).

    I started by extracting the edges from the surfaces in your file. Used DevSrf to create the new surfaces. The upper chine needed to be extended to create the upper surface, and then I trimmed the resulting surface on the centerplane. (Created a centerplane surface for the trim.) Used UnrollSrf to unroll the panels.

    DevSrf should be in Rhino 5; it needs to be downloaded for Rhino 4.

    Reason for extending the upper chine: DevSrf only creates a single developable suface, not a polysurface like Loft sometimes does. This means that the surface always ends at ruling lines, and except for special cases or luck the surface created won't go the ends of both curves. Simple solution, just extend which ever curve it ends at and then trim the result.

    I tried using Loft with the Developable surface option but it didn't like the curves.
     

    Attached Files:

  8. DCockey
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    DCockey Senior Member

    How did you create the curves used for generating the panels? Was it by fitting curves through points?
     
  9. Dean Smith

    Dean Smith Previous Member

    Usually I check the squished area against maxsurf also bringing it back to R4 and overlaying
     
  10. DCockey
    Joined: Oct 2009
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    DCockey Senior Member

    What do you check against in MaxSurf? I'm not familar with MaxSurf.

    Why not modify the surfaces in Rhino until they unroll using UnrollSrf and then you know they are developable?
     
  11. Dean Smith

    Dean Smith Previous Member

    boat building designing is an art form
    If you want a developed shape then you restrict yourself somewhat
    i have unrolled stuff in r4 that in theory should not have unrolled and it came back against maxsurf spot on
    Maxsurf is a very expensive design suite
    perhaps you may look at FREESHIP it is free. From there you can export into R4 I believe
    I am sorry cant help you much I,m away from main workstation Besides I am not an expert in rhino, can only speak in broad terms about the results I have achieved
     
  12. DCockey
    Joined: Oct 2009
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    DCockey Senior Member

    If the boatbuilding method which will be used needs developable surfaces then the boat should be designed with developable surfaces.

    How stringent about meeting developable requirements is the tool you use in MaxSurf for evaluation? Does it allow stretching and compression deformation like Squish and Smash do in Rhino?

    Why the comment about FreeShip? I don't have any problems using Rhino.
     
  13. Dean Smith

    Dean Smith Previous Member

    thats good then, maxsurf will flatten most shapes, let me see if I can open yours
     
  14. Dean Smith

    Dean Smith Previous Member

    I have just unroleld the topside plate in r3 no probs do you want it?
     

  15. Dean Smith

    Dean Smith Previous Member

    here is the plate unrolled
     

    Attached Files:

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