What's the most efficient way to fair lines from a table of offsets?

Discussion in 'Software' started by adt2, Mar 9, 2012.

  1. adt2
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    adt2 Senior Member

    It's got a 54" x 120" cutting bed that's open on both ends - so theoretically, with proper fixturing and some careful layout, I could cut essentially an endless piece as long as it's not wider than four and a half feet.
     
  2. Submarine Tom

    Submarine Tom Previous Member

    WOW, that's Texas sized!!

    -Tom
     
  3. adt2
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    adt2 Senior Member

    Yeah, it started out as a homebrewed 2x8 machine for milling frame patterns (since long, skinny pieces seem to be the lion's share of boatbuilding). As soon as I got the machine finished and working, I got an offer for paying work (using the machine) that required a bigger work surface. So, off to the drawing board I went.

    Turns out, for less than $200, I was able to stretch the width to accommodate a full sheet of plywood. Been a fun project, although a trifle more expensive than I originally planned.
     
  4. jehardiman
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    jehardiman Senior Member

    If you have fair sections to CNC, like you stated in post #4, why do you need a fair surface? FWIW, unless you are using thin steel, the developed surface will not allow you to generate CNC planks without a lot of hand work. And the planking is going to seek its own fairline anyway. Better to make and fit a plank then pull the offsets off it for series production. Don't get caught up in a false sense of perfection, it's not needed.

    Anyway...

    Yep, that is the way we do it in the office. Once you have set up the original stations, throw up several end-to-end low count splines that get close to most of the stations, but only hit the stem, transom, and midships section. Fair the splines then cut across the splines and generate stations fair to the splines then sweep out the surface. The final surface is then fair because all the tangents and the station cuts are aligned. Generally the difference between the TOO and the generated stations is within normal construction tolerance (1/8-1/4").
     
  5. adt2
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    adt2 Senior Member

    Wasn't planning to generate CNC planks; just want to CNC the frames. Wasn't sure how fair the frame layout had to be to allow the planking to lie fair. I guess it depends on how thick the planking will be (i.e. 2x4 planks would fair themselves better than 1/4" x 3/4" planks over the same frames).

    I suppose I could loft the boat full-size, then use the faired lines to generate CNC toolpaths. Frankly I have no idea where I'd loft a 50' boat. I've got enough floor space to do the body plan, but I couldn't do the profile or the plan view because my workshop is only 40' long.
     
  6. wet feet
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    wet feet Senior Member

    Any reason for using Sweep 2 Rails rather than creating a lofted surface?My limited experience began with creating splines at stations from offsets and creating a lofted surface,then tweaking control points to attain fairness.At which point you can offset the surface to derive the shapes to send to the CNC.
     
  7. adt2
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    adt2 Senior Member

    I used Loft when I first started using Rhino, but I had some problems getting surfaces created and somebody around here suggested the Sweep 2 Rails command instead, using intermediate sections to get the desired shape. Honestly I don't know enough about Rhino to know what makes one better than the other....I just use whichever one works that day...:)
     
  8. TANSL
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    TANSL Senior Member

    For many years I worked for several yards developing the information needed to build large blocks of steel : definition of plates of the hull, pieces of the structure, nesting of all that and processing them to obtain files for numerical control cutting machines. I did that by means of my own software, based on AutoCAD drawings. Can this be of help?
    Ignacio Lopez
     
  9. TANSL
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    TANSL Senior Member

    Years ago everything was done at 1:1 scale, for vessels over 100 m in length. The longitudinal profile was divided into two sections, fore and aft, and were superimposed on the same surface, a floor of wooden boards.
    Later went on to perform the same work on a plotting table, at 1:10 scale. Currently is done by the computer. I do, quite easily with AutoCAD, with a screen of sufficient resolution, using splines or polylines, as appropriate. Splines are precisely the same soft lines achieved with the bead of the draftsman.
     
  10. The Loftsman
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    The Loftsman The Loftsman

    This one always gets me going,
    A table of offsets is in most cases just a table of the original scantling offsets produced by the N/A when doing start of design process, the said offsets are not all that fair and just a guide for the loftsman to start his work from, the offsets do not have endings and are only produced at frame stations 10 to 12 they are not finished "Faired" offsets for this you would need to refer to the "Offset Book" a set of finished faired offsets including all landings decks etc,etc in other words the position where every point required to fair the vessel is located.
    Just to think that a small table of offsets can be input into any software and then somewhere a magic design a boat button is pressed is a wee bit naive to say the least.
    There are no shortcuts to a finished faired hull, just faster ways of making mistakes thats all.

    Cheers
     
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  11. gonzo
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    gonzo Senior Member

    As a loftsman, I totally agree. There is a group of new designers that believe a computer programmer, with no understanding of boats or sense of aesthetics will fair the lines for them.
     
  12. TANSL
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    TANSL Senior Member

    Only with the hope that readers comming can compare the opinions, I'll answer what is being said above. I started working as a naval architect in 1971, dealing primarily with the smoothing of the forms of ships and, from there, generate all the calculations of the hull and, more importantly, the construction drawings of the hull. In those days everything was done by hand. I participated in the implementation of computer systems in two Spanish yards, just to make all these crafts through the computer. Later, during 15 years as a freelancer, I had to handle several programs in naval architecture and to generate information for the workshops. I developed my own applications for my work to reduce staff and increase competiveness. I therefore know well how to do our work with computer and of course "I WILL DO IT BY HAND."
    Regardless of design, the forms are or are not pretty, that's another topic altogether, I assure you that computer are currently the only tool that a prudenet designer can use. But of course, all opinions are valid and respectable. There are professionals who think that a pretty picture is a good boat, but this need not be true, or that their quality as a designer is measured by the 3D model or video, with girls included, which is capable of performing. And of course, if you can not do things "by hand" or do not have clear concepts of naval architecture, it is impossible that the computer allows you to design boats.
    Greetings to everyone
    Ignacio López
     
  13. The Loftsman
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    The Loftsman The Loftsman

    Space

    Hi
    Space would not be a problem if you were to fair the full size lines, as from the straight of side (if there is straight shape each side of mid-ships) you only need to loft the shape for'd and aft and they can be placed on top of each other so your 50 foot could become 25 feet



     
  14. DCockey
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    DCockey Senior Member

    There may be a difference in terminology regarding "table of offsets" between "ships" and "boats". My understanding is that a table of offsets for a boat from a naval architect or designer would usually include offsets at all stations as well as the stem, keel and transom/stern post. Traditionally these offsets would then be faired during lofting, and usually patterns lifted directly from the lofting. I'm sure some designers and builders of boats work differently.
     

  15. jehardiman
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    jehardiman Senior Member

    You left out the most important line, the bearding line. No, lines include all the points that the NA think is important. For most small wodden private yachts as you seem to apply it, this is actually very few lines as it is expected that the builder is going to fill in the missing detail to the finish requirements and shop practice. For a steel ship build, there will be all sorts of other lines, as Loftsman says, a whole booklet of them. Mostly to help lay out the easily developed areas (flat or single rolled), and the points you have to hit to make contract/stability requirements.
     
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