Newbie developable surface tool questions

Discussion in 'Software' started by Anatol, May 29, 2015.

  1. Anatol
    Joined: Feb 2015
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    Anatol Senior Member

    I am designing a stitch' n'glue style ply hull - a proa - so double ended, reversible. I am looking for a software tool which has developable surface capability. What I understand by this is: have the capability to model a form, ie a hull, out of multiple flexed flat panels which can be unflexed and drawn out as panels of flat planes to be cut out of plywood, and then assembled. If the tool would output as full scale plans on paper or drive a lasercutter, that would be helpful. That seems pretty straightforward. I thought this would be relatively trivial but in turns out not to be. After some research and learning it turns out this is not a capability AutoCad and Inventor do not do it. I'm told Rhino has these capabilities - can anyone confirm or suggest?

    What is more demanding is to be able to import a model, say a matchbox, distort it, then have the software test whether the form is still developable, and define the relevant flat panels. Having it simply 'shatter' the form into tiny developable 'shards' would not be helpful :)

    I know enough about software to know its always the implementation of someone's idea of the right way to do something. As often as not I think they're wrong:) Sometimes those approaches are heavily theoretical and sometimes they are implementations of traditional (real world) procedures. It seems like there must be two quite different approaches to doing this kind of modelling. You either begin with entirely abstract, even impossible forms and equip the software with tools to resolve these forms into developable forms , or you constrain construction of forms at the outset by defining the possible behavior of the simulated material. I'd assumed that the latter approach would be 'normal' but it seems the former is.

    (background - I've been in computer graphics, computer science and robotics circles for 25 years. I have experience in diverse kinds of making from blacksmithing to vacuum forming, domestic construction, welding, and of course boat work of various kinds. But I'm not a naval architect and I'm not familiar with contemporary CAD tools.)
  2. TANSL
    Joined: Sep 2011
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    TANSL Senior Member

    You could specifically tell us what shapes you want to develop. Perhaps, if we know what you're talking about, we can tell what tool and how you can get it.
    BTW, whatever it is, it's hard not to get with AutoCAD.
  3. DCockey
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    DCockey Senior Member

    Rhino does a good job with developable surfaces though problems occasionally occur. The Unroll command will unroll a developable surface to flat (provided the structure of the surface is correct *).

    Rhino has several ways to check for whether a surface is developable. One method is to simply try unrolling the surface and see if it works and if the area change is sufficiently small. Another method widely discussed is to check Gaussian curvature and see if it is sufficiently close to zero, but the numerical value of Gaussian curvature depends on the unit system and object dimensions, and what appears to be very small Gaussian curvature may not be sufficiently small. Another way to check if a surface is developable in Rhino is to use Curvature to check the principle curvatures at a number of locations on the surface and verify that one of the principle curvature is sufficiently close to zero (ie straight).

    DevSrf is the best (free) tool in Rhino to create a developable surface from two curves such as the sheer and chine or chine and keel.

    When creating developable surfaces starting with the two curves one of the curves will need to be extended at each end and the created surface then trimmed to the desired length (unless the corresponding ends of the curves happen to lie on the same ruling line).

    Rhino can be downloaded for a free 90 day trial.

    * To be unrolled in Rhino a surface must have one set of isocurves corresponding the ruling lines. This is generally not a problem with developable surfaces created in Rhino but can be a problem with arbitrary imported surfaces.
  4. Anatol
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    Anatol Senior Member

    thankyou for this excellent advice.
  5. ludesign
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    ludesign Senior Member

    TouchCAD provides a different approach to surface development, as it has a true dynamic link between the 3D panels and flat panels. This means that any changes made in the 3D model can instantly be seen as a flat panel. You can even gently nudge 3D shape controls and instantly see the result in realtime, even when simultaneously dealing with hundreds of panels in a complex cut layout. In reality, optimising panels for flat patterns is an integrated part of the design process and not something you do afterwards. You also use is to optimise the use of material, making it an integrated part of the design process.
  6. Anatol
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    Anatol Senior Member

    thanks. I'd seen TouchCAD before. Currently I can't justify the outlay for a single project. I looked on the website but did not see an educational pricing (?)
  7. SukiSolo
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    SukiSolo Senior Member

    I'd confirm Rhino does a pretty good job of dealing with developable surfaces. Very much as David describes above, however a little more deviation is possible sometimes, when using timber as the build material. Be careful with it but some ply and solid in thin form will in fact stretch in 3D not just 2, just a fraction more than the program may suggest. For this you need your own real world experience to help you - no other CAD tool would do it for you anyway!.

  8. Anatol
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    Anatol Senior Member

    thanks! Yes, past experience with ply indicates that you can get minimal bending perpendicular to the axis of main bend. less than 5% I'd guesstimate
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