Rhino 5 - material thickness

Discussion in 'Software' started by rwatson, Jul 6, 2013.

  1. rwatson
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    rwatson Senior Member

    I have been playing with Rhino 5,

    When drawing a hull, the varying thickness of plywood is important to represent for accurate sizing.

    Does anyone have any hints for the most efficient way to create thick materials, and what sort of object they should be done in ?
     
  2. DCockey
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    DCockey Senior Member

    Several methods for creating flat "plywood" in Rhino:

    1) A flat rectangular solid with edges parallel to the axis can be created using Box. The solid can be rotated and trimmed as desired.

    2) A flat sheet of plywood of any shape can be created using ExtrudeCrv. Create a planar curve of the outline of one face of the plywood. Then extrude the curve to the desired thickness using ExtrudeCrv. Use the Solid option to create an enclosed solid.

    3) A flat sheet of plywood of any shape can be created using ExtrudeSrf. Create a planar surface of one face of the plywood. Then extrude the surface to the desired thickness using ExtrudeSrf. Use the Solid option to create an enclosed solid.

    For Curved plywood first create a surface representing one face of the plywood. To ensure that plywood can actually be bent to the shape the surface needs to be developable. This can be done using Loft with the Developable option. Developable surfaces can also be created using DevSrf which is my preference. However DevSrf needs to be separately downloaded and installed as a "Plug-In".

    After a surface representing one face of the plywood has been created then the face of the plywood is created using OffsetSrf. The edges can be created and combined to form a solid using the Solid option.
     
  3. rwatson
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    rwatson Senior Member

    Thanks David. That's exactly the types of hints I need.

    My mind wasn't up to the 'bending' of flat panel stage yet, but that is a real bonus, as it will help visualise the build.

    On the bigger boats, its a hard call to know how large to build the panels out of several sheets of plywood before it gets too heavy to handle, but single sheets of ply are hard to hold down on the moulds and get a fair surface.

    Many thanks for that.
     
  4. DCockey
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    DCockey Senior Member

    You can also unroll a developed surface using the UnRoll command. Use either the inner or face of the plywood, or if you want to be theoretically more exact create a mid-surface between the two faces using the TweenSurfaces command. Be aware that the tolerances for UnRoll are set rather loose and the ability to "unroll" a surface using it doesn't mean the surface is sufficiently close to developable to be made from plywood.
     
  5. Ad Hoc
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    Ad Hoc Naval Architect

    In what way do you mean. I'm not sure I follow?
     
  6. rwatson
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    rwatson Senior Member

    The problem occurs when you are designing frames, stringers etc to be cut by cnc routers.

    if the outside dimensions are established, and the hull plywood is say ... 12 mm thick, then all the frames have to be cut ~13 mm narrower to accommodate the plywood shell.

    Also, if you are cutting stringers to mate into the internal frames, and the frames are say 10mm thick, the stringers or 'furniture' have to meet either side of the frames, allowing for the thickness of the 10mm frames.

    However, if you just represent the hull plywood as a single line, the cnc router will make the inside frames too wide, and force you to exceed the outside dimension of the hull, and the hull panels themselves wont join at the chines correctly during assembly.

    or - a single line representing the frames, makes the stringers or internal furniture too long, and not able to fit between frames.

    CNC cutting is a precise business.
     
  7. TANSL
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    TANSL Senior Member

    Perhaps the words I use are not adequate because of my limited English proficiency. But what I do dominated is shipbuilding and know that, many years ago, shipbuilders have solved that problem: you have to work with the "moulded lines". The experts on the subject will understand me and can better explain Mr. rwatson what I'm talking about.
     
    Last edited: Jul 7, 2013
  8. rwatson
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    rwatson Senior Member

    Thanks TANSL, any help is appreciated.
     
  9. Ad Hoc
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    Ad Hoc Naval Architect

    Well, it seems you work somewhat differently to me, hence the clarification question to confirm my suspicions.

    We always use moulded lines. Thus plate thickness is not required as there is no offset that is needed.
     
  10. rwatson
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    rwatson Senior Member

    I have no idea what moulded lines are. What software aree you using ?
     
  11. Ad Hoc
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    Ad Hoc Naval Architect

    It has nothing to do with software. It is how lines are drawn and how the lines are then taken to produce frames. See below graphically:

    Moulded Line.jpg

    If you image standing inside the boat, the intersection between the frame web and the shell plating is the moulded line. This is the line which is taken from the Lines Plan.

    So if the hull plating changes thickness, it does not alter anything, the frame web depth remains the same. The hull plate has changed thickness, nothing else. Thus the actual displacement is therefore changed slightly, as it is the distance from the moulded line to the exterior line of the hull (the plate thickness). Which is also why you have moulded displacement and actual displacement in stability software, and in the software one is requested to input the plate thickness, since this accounts for the "increase" in the volume as such from moulded, inside line, to displacement, the outside line ie. plate thickness.
     
  12. TANSL
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    TANSL Senior Member

    As stated in the image shown by Ad Hoc, it is "BASIC ship theory".
    Rwatson, you can learn a lot from the lessons of Ad Hoc and you'll see that if you are able to understand and follow hes teachings, your problem will be gone. Never too late to learn basic shipbuilding.
    Cheers
     
  13. rwatson
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    rwatson Senior Member

    Oh sure, I can understand the concept of the moulded line as a lofting and building concept. But when you set your CNC router to cut the frames, it doesn't understand the concept. You have to apply the specific measurements, and no router understands the 'moulded line' terminology.
     
  14. TANSL
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    TANSL Senior Member

    I'm afraid you're not understanding anything and never in your life have prepared a piece to be cut by CNC. Try it and if you understand the concept of the "molding lines", you'll see that it's very easy. The router does nothing by itself, is not capable of thinking. It will not do anything that you do not tell it to do.
    There is nothing better than knowing what one is talking about to talk about it. You'll always have this forum to teach you what you do not know. Study and good luck.
     

  15. bhnautika
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    bhnautika Senior Member

    Rwatson If you use your Rhino hull surfaces as the mould line. Put sections or contours lines through that to get your frame edges. If you want to use it as the outside of the hull as your starting point use “offset surface” (required thickness) then add the sections/contours to that new surface, this will give you a frame outline allowing for the varying thickness due to angle of hull to frame
     
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