Devsrf command

Discussion in 'Software' started by Ardi, Feb 27, 2023.

  1. Ardi
    Joined: Sep 2021
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    Ardi Junior Member

    Hello everyone,
    Is there any tutorial about devsrf command in rhino? I'm not sure how to use the command correctly so that it can produce an accurate developable surface.
    Thank you for the help. Cheers
     
  2. Matthew777
    Joined: May 2020
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    Location: Thailand

    Matthew777 Junior Member

    This command is talked about extensively in the Rhino CAD forums. I would highly recommend searching there for more information and discussions about it.

    McNeel Forum https://discourse.mcneel.com/

    There are also quite a few tutorials that work with this command on YouTube.

    You really need to be more specific about what you are asking to get a more meaningful answer, sorry about that.
     
  3. Ardi
    Joined: Sep 2021
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    Ardi Junior Member

    Hello, thanks for the information.
    I did a 6mtr boat design and send the cnc plan to the cutting workshop, but the man told me that there is a problem with my bottom plate, he said that the frame in the front area should have a little curve in its bottom part. Because when the bottom pulled together there will be a curve in bottom plate. If the bottom of my frame is flat then there will be a gap between the frame and the bottom.
    He told me to use devsrf command to rebuild the boat's bottom plate, but I cant find a proper tutorial how to do that.
    That's my problem..
     
  4. Ardi
    Joined: Sep 2021
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    Ardi Junior Member

  5. TANSL
    Joined: Sep 2011
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    TANSL Senior Member

    If you give those lines some curvature, the surface is no longer ruled and is no longer developable, so the command you want to use is likely to not work correctly.
    An observation: the shapes of the boat must be as the designer, who is you, deems appropriate, not as the operator of the cnc machine likes them. imo.
     
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  6. RAraujo
    Joined: Apr 2010
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    RAraujo Senior Member - Naval Architect

    A ruled surface is not always developable but a developable surface is always ruled... A developable surface is a particular case of ruled surface (A developable surface, also called a flat surface (Gray et al. 2006, p. 437), is a ruled surface having Gaussian curvature K=0 everywhere).

    Usually there should be some curvature in those stations. The way your lines are drawn it is a ruled surface but it is, most probably, not a developable surface. Try to draw the surface generators...
     
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  7. TANSL
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    TANSL Senior Member

    Totally agree, let's think, for example, of the hyperbolic paraboloid. But knowing that, which is very interesting, won't help the OP much.
     
  8. baeckmo
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    baeckmo Hydrodynamics

    RAraujo has got it right. If the bottom is supposed ("designed") to be developable, and the stations' average bottom rise (defined by the line beween keel and chine) is increasing going forwards, then there has to be curvature in the stations. The straight rulings in the multiconical surface will pass from points on the keel and diagonally back and out to the chine line.

    Drawing a bottom surface with straight stations and varying deadrise will result in a faceted surface consisting of triangles with a straight hypethenuse between lower front and outer back corner. It can only be smooth if both chine line and keel line are curved (have "camber"). The cnc guy knew that this would not be a good shape; he knew his stuff, but the "designer" did not.
     
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  9. TANSL
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    TANSL Senior Member

    It seems that things have changed, and a lot, because, having participated in the development of the construction drawings for dozens of metallic ships, all of them with non-developable surface areas, I have never had to change the shapes of a hull because of opinion or guided by the advice of a cnc guy. But I cannot assure you that things are not like this now because I have not worked for metal hull shipyards for some years.
    For the rest, I totally agree with what @RAraujo and @baeckmo say.
     
    Last edited: Mar 5, 2023

  10. wet feet
    Joined: Nov 2004
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    wet feet Senior Member

    Might I suggest getting hold of a copy of this book and reading the part devoted to conic sections?Sam Rabl's book is quite handy too.
    [​IMG]

    It will demonstrate that while straight lines can appear at the bow,they will head in the direction of the apex of the cone.Which is likely to be some distance to one side and below the keel line,if the bow is considered.The fore and aft location of that apex is unlikely to be perpendicular to the centreline where a particular frame lies and it is this that tends to create a small amount of curvature when a section that is perpendicular to the centreline is used for framing.After a bit of experimenting with estimating where the apex is it is possible to ease the workload when making a first estimate of the shape.Which is probably when it is time to use Devsrf,which I admit to not having used but am now curious about understanding better.The builders of the boat will have an easier time if the panels are developable and this may well be reflected in their costs to the relief of the person paying for the job.

    In essence,the keel and chine lines are created by the intersection of the surfaces,rather than the surfaces being created by the lines that are selected for the surfaces to be bounded by.
     
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