Simple hull help? (3dm)

Discussion in 'Software' started by DANGERSPEY, May 28, 2006.

  1. DANGERSPEY
    Joined: May 2006
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    DANGERSPEY Junior Member

    Greetings all. I hope it's o.k. to request help on ones first post so here goes.

    I've been goofing around for a couple of years on a real simple hull design and would really like to start cutting metal soon. This hull has 10 deg or so of deadrise all the way through to be used on inland rivers with an o/b jet for power, as I'm sure some will point out how silly this design would be for ocean use.
    I'm pretty happy with the design the way it is now although when I display the curvature graph on the chine it looks kinda screwy. When I attempt to "fair" the chine it does get smoother but it puts a curve in the part of the chine that's supposed to be straight.
    Any comments would be appreciated.
    Ryan
     

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  2. E Hanson
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    E Hanson Junior Member

    I tried to answer you query, but then my post was lost during an issue invlolving "logging" on. If this posts, I will try again with an answer for you.
     
  3. E Hanson
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    E Hanson Junior Member

    Ok, I can post, so here is a way to fair your hull lines. For this I am going to use the shear line for an example. The chine and the keel are done the same way.

    Step one: draw a straight construction line from the transom fwd. this line needs to be at the height and beam that you want your shear line to be.

    Step two: Rebuild your surface control line. It should have 5 control points and be degree 3.

    Step Three: Turn the control points on. (note these are NOT the edit points, the control points only lie on the line at the start and end of the line.)

    Step Four: Working from the transom fwd, drag the aft 3 control points so that they lie exactly on your straight construction line. Use the "nearest" snap. This will force you surface control curve to be straight and tangent to the construction line.

    Step Five: Drag the fwd control point to the top of your stem line.

    Step Six: The last control point (#2 counting fwd to aft) is now left in space. drag it in plan and in profile until you get a shear line you like. turn on the curvature combs and have a look at the curvature.

    Step seven: Adjust the control points until you are happy with the line. Keep the aft three points on the straight construction line. Add points if you wish greater control of the shape, but realise that more points are harder to fair.

    Step eight: Repeat the fairing process with the chine line and the keel.

    Step Nine: loft the new hull and topside surfaces. Use the "developable" surface option.

    I hope this helps, and good luck.
     
  4. josch
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    josch Junior Member

    smooth surfaces in Rhino

    The procedure which is described above works pretty well, ... but could be improved.
    Especially with freeform surfaces and especially in Rhino, whose surface qualites are bad compared to say parametrical programms you should try to build the bottom out of four control lines instead of three
    (transom, chine , keel)´

    At the very front where these three lines intersect EVERY program produces unsteady surfaces. So if you start and dont let the three lines intersect each other (may be just a millimeter) by building a fourth line then the program can find a fair solution for your surface. :)

    The missing millimeter doesn´t harm as if you work with surfaces instead of volumes and it will be welded together anyway.

    Together with the above mentioned procedure you will certainly get what you are looking for.

    regards
    josch
     
  5. DANGERSPEY
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    DANGERSPEY Junior Member

    Thanks for the response guys! I'll put your suggestions to use and see what I come up with. I'd rather do it now instead of "tweakin" it with the Skil saw when I start tacking it together.

    A couple more questions. Is the "crv2view" command the best way to come up with chine line for the 3d model?
    If the chine lines are fair in the top and side profiles does that mean the 3d shape they produce should be fair?
     
  6. josch
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    josch Junior Member

    lines control

    I don´t know the command you are mentioning, .... the curvature analysis you already know is (utility menu under --> analyse --> curve --> curvature control) the only way of fairing lines I know but it works well and it counts true in every perspective.
    One more thing you could know. For the case that your chine consists out of one ore more merged lines you will never get a good result.
    You have to rebuild the line before you start fairing.

    So to answer simply if I understood you question right - yes - it should be fair.
    But consider my previous post just when you build your surface out of 4 lines.
     
  7. DANGERSPEY
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    DANGERSPEY Junior Member

    Josch you are correct, 4 lines are the way to go. See the simple file I attatched. It uses the "crv2view" command. I think it might be useful.

    Instead of lofting I would use the "sweep 2 rails" to develop the surface.
    Ryan
     
  8. E Hanson
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    E Hanson Junior Member

    The "curve from two views" command will help you get started, but I would always rebuild the result and confirm fairness. I use the comand often when importing lines frrom a 2D drawing that I am building into a 3D model. I also find it works well when you have an idea of a shear line, but can only think of it in terms of plan and profile.

    As for lofting VS. sweeping...

    If the hull you are designing is to be made from aluminium, or plywood, you really should loft with a developable surface. A two line sweep will produce a nice smooth surface, but it will be concave in the fwd sections of the hull. You can check this with the Gausian curvature analysis.
     
  9. BarendB
    Joined: Aug 2006
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    BarendB New Member

    fairing in Rhino

    Hi everyone. My name is Barend and I'm from the Netherlands, Europe. I'm currently working on a little steel hull measuring 6 meters wich is being 'designed' in Rhino. It's my first design and the first time I work with Rhino.

    I have a few questions about Rhino:

    For creating the surfaces I use the 'sweep 2 rails' command and make the surface developable. When I unfold the surface I get a nice curved surface. I want to cut the steel sheets with a cnc cutter so I have to export the surfaces to a Autocad-file. For this I use the command 'export'.
    When opening the file in Autocad, the unfolded surface isn't as nicely curled as in Rhino but it seems the line is made of short straight lines. How do I get a nice surface in Autocad to send it to the cutting firm???

    Second question:
    When I make a 'section' to make cross sections, I notice that the sectioned surface (now a vertical line) isn't a straight line. The boat is a hard chined tender and I was surprised to see that that line isn't straight. Can I use a feature to keep the surface 'flat shaped'..?

    I add a pic of my rendered model..

    Kind regards!
    Barend
     

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  10. Arvy
    Joined: Jun 2005
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    Arvy Senior Member

    Hi Barend,

    As i am only using rhino to design the hull surface and do the rest of the designing in autocad (have been using autocad for construction designing of yachts and other vessels for years, it works great for that but unfortunately not for designing freeform surfaces), i also had to export the shape to an autocad file. Doing that i also did find a lot of polylines consisting of straight lines.

    What you must do is set the export parameters to the right value. There is one parameter that you can set during the export which is called something like max angle, (don't know the exact name it is on the bottom part of the dialog you get when saving to an dwg file i believe that is it is the fourth from below .. de vierde van onder..). When you set this parameter to a low value (i use 1 but i will also be fairing the lines in autocad in a later stage) you will get a much better result. You should also experiment with the other settings.

    Let me know if this did the trick,
    Grtz
    Ronald.
     
  11. okoyunlu
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    okoyunlu New Member

    Dear Dangerspey,

    May be it is a long way but,
    1. after you have your surface's border
    2. export it as extention of .dxf
    3. select spline while exporting
    4. open the .dxf file using auto-cad
    5. redraw with polyline command (come close up to 3 mm is a good value on steel plates)
    6. Don't forget to add extra extention on one side of bending direction about 25mm (is an emergency)

    Note : If you export from rhino as polyline, it is hard to check precision.

    Best,
    Onur
     
  12. Raggi_Thor
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    Raggi_Thor Nav.arch/Designer/Builder

    I don't think so.
    It's better to draw a curve, degree 3, first in plan view and then drag or nudge the control points in profile view to make the shape you want. With 5 points it will be very smooth.

    It's also good practise to extend the defining curves (keel, chine, gunwale) to the other side of the center line, then use edgesurf between two and two lines, then trim along the center line. With some trial and error you get a nice bow profile and developable panels.

    This is described a tutorial, I think.
     

  13. Chris Ostlind

    Chris Ostlind Previous Member

    Prepping for CNC work from .dxf files

    Hi Barend,

    When sending Rhino files to a CNC device to cut the hull panels, I do the following:

    1) Select everything and project it to the CPLane in the Top view

    2) Use DupBorder on the surfaces and then delete the surfaces. You will be left with the outline edges of the former surfaces.

    3) Use the settings below when you are prompted after initiating the Save As (dxf) function:

    AutoCAD version
    Release 12

    Save curves as
    Polylines

    Save surfaces as
    Polygon meshes

    Save polygon meshes as
    Polyface meshes

    Curve options
    Project to plane
    Project to cplane
    Use simple entities

    Simplify tolerance 0.05
    Polyline max angle 10
    Polyline chord height 0.01
    Polyline seg length 0

    The above save settings have produced clean files that are easily cut by any good CNC software. Make sure that you nest the patterns efficiently and save them to the proper media for the CNC shop.

    Please post some images of the cut panels and how you assemble them in the shop.

    Chris
     
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