digital projector for pattern tracing

Discussion in 'Boatbuilding' started by BlackSnow, Feb 26, 2010.

  1. BlackSnow
    Joined: Feb 2008
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    Location: Iowa

    BlackSnow Junior Member

    All,

    I have been following this forum almost daily for several years but have posted only a few times. First, let me say, that I have found the posts of the forum's many talented desingers and builders very stimulating. I have the utmost respect for many of you and feel like I have found a home of kindred spirits.

    I have built several small ply/epoxy/glass stitch and glue boats, and am now in the process of building a 23' cabin cruiser of said method. I have recently decided to take the step from builder to designer, with my current interest being small boat design. Because, as we know, there are not enough small boat designs out there already ;). I have spent nearly 30 years canoeing and feel I have the experience to know what works and what doesn't work. Like many of you, I have the notion that I posses unique insights into the design of certain aquatic conveyances. Whether this is true or not will be borne out through my endeavors over the next several months. I am a registered professional mechanical engineer, so I believe that I have more than a casual knowledge of forces, acceleration, material design, etc...

    In any case, please excuse the long introduction, but I wanted to make it clear that I am not a "fly-by" poster working on a school project or some such assignment. That being said, I am posing a question to the group regarding the use of modern technology to facilitate the jump from design to construction.

    My question being: Has anyone used a digital projector to enable quick tracing of "hulls"/"freeship"/"delftship" stitch and glue patterns onto plywood construction material? In perusing ebay, I have noticed that there are many used computer/TV projectors available for little cash outlay. In my searches of this site and others, I have not discovered significant evidence of anyone using this technique with success. The only reason I can think of why this wouldn't work is if the projection wouldn't be accurately portrayed between the design program and the construction material. Obviously, the distance between the projector and plywood needs to be adjusted carefully to get the proper scale accuracy. Vertical/horizontal alignment of the lense must also be dead center to the piece of plywood. I am concerned, however, that in the projection process, there will be distortion that will introduce enough inaccuracies as to render the effort unworkable.

    My first thought has been to project a simple 3-4-5 triangle and verify the projected dimensions to see if they are proportionally accurate. Before I commit to pursuing this experiment, I ask that anyone trying or hearing about this approach chime in with advice.

    Thanks!
     
  2. Hunter25
    Joined: Mar 2006
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    Location: Orlando

    Hunter25 Senior Member

    Lens distortion from a screen image to a full size image will be substantial, without software compensation. Lofting is not that hard to do and will side step the projector problems in a conventional way.
     
  3. ancient kayaker
    Joined: Aug 2006
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    Location: Alliston, Ontario, Canada

    ancient kayaker aka Terry Haines

    Nothing to stop it working in theory, errors in the setup and basis projection system are the problems. It may be sufficient to project and simple pattern that could easily be measured, but it should cover the entire area that is expected to be used to ensure edge arrors are picked up and several intermediate grids as well. A simple rectangular net should suffice. Use several of these patterns though, in case there are odd effects like thermal drift. This all asssumes line thickness is acceptable.
     
  4. BlackSnow
    Joined: Feb 2008
    Posts: 7
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    Location: Iowa

    BlackSnow Junior Member

    Thanks for the advice guys. I will plan on proceeding with this approach, since it looks like I can get ahold of a projector for $50-$75 US. If it is a failure, I will put it in my basement and enjoy the new home theater system. It will be sub-par according to today's standards, but what the heck.

    I realize that lofting is not that big of a deal. I will be happy to do that when I have a "build worthy" design. I just like the idea of embracing new technology when the opportunity presents itself. I am also hoping to be able to set the projector close to the building material to allow for its use in balsa (or other material) model building. This is where I would be most able to use the possible speed advantage to crank out multiple quick-to-build models, so that I can evaluate shape and make adjustments accordingly. I also know that this technique can be used on small scale models using an old-school transparency projector. I may try that approach if the digital projector experiment is not successful.

    I will report back on this in a few weeks, whether I am successful or not.

    Cheers!
     
  5. Hunter25
    Joined: Mar 2006
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    Location: Orlando

    Hunter25 Senior Member

    Lens distortion will will show up around the perimeter of the projection. The size of the enlargement and the lens used will dictate how much distortion. The bigger the enlargement, the more the distortion. A simple test is to draw a straight line on the transparency projector and then blow this up to 8' long on a wall. Snap a line through each end point and you'll see the distortion, if it is not obvious just by looking at it.
     

  6. gonzo
    Joined: Aug 2002
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    Location: Milwaukee, WI

    gonzo Senior Member

    Make a couple of straight parallel lines and project them. That will show you how much distortion you are getting.
     
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