Laser cut core material?

Discussion in 'Fiberglass and Composite Boat Building' started by Mike Inman, Oct 30, 2018.

  1. Mike Inman
    Joined: Oct 2018
    Posts: 55
    Likes: 6, Points: 8
    Location: Jacksonville, Florida

    Mike Inman Junior Member

    Instead of beam compass and hand saw, is there any established practice of transforming sheet materials like thin plywood or foam core into "compound developable surfaces" as described here: Plywood, double curvature impossible ? http://forum.woodenboat.com/showthread.php?174759-Plywood-double-curvature-impossible&p=4089027#post4089027

    I was thinking, for a one off or short run design, that a hull shape could be designed, forms built like bulkheads to guide the shaping, and multiple layers of thin plywood or foam panels pre-cut to form into the designed shape when laid onto the guides... of course, all things are possible - what my real question is, is: as relatively cheap as laser cutters are these days, are there established reasons why this isn't described more often, or are the established methods just more comfortable?
     
  2. fallguy
    Joined: Dec 2016
    Posts: 2,986
    Likes: 332, Points: 83, Legacy Rep: 10
    Location: usa

    fallguy Senior Member

    Cold molding is labor intensive.

    It all comes down to ease of building.

    Lasers burn. Routers cut. I had my forms cnc cut, but they didn't put the bevels in-required handwork...took me a day to realize the odd looking lines for'd.
     
  3. JamesG123
    Joined: Mar 2015
    Posts: 655
    Likes: 75, Points: 28, Legacy Rep: 10
    Location: Columbus, GA

    JamesG123 Senior Member

    Plywood and foam are not the same thing. Perhaps you mean wood veneers laminated via cold molding like fallguy is deducing?

    Whenever possible you do not want to "torture" plywood because it induces sheer and all kinds of stresses within and between the layers into what is supposed to be a simple core to transfer stress and loads from one skin to the other. Foam will stretch and bend, ply only does so grudgingly because it is designed to resist the forces you are trying to make it bear. You are just asking for laminate and then composite failure. "Cold molding" creates a plywood in the desired shape, but as mentioned is a highly labor intensive process unless you're set up for mass production with a press, mold, etc.
     
  4. fallguy
    Joined: Dec 2016
    Posts: 2,986
    Likes: 332, Points: 83, Legacy Rep: 10
    Location: usa

    fallguy Senior Member

    I 'tortured' my foam. Although torture is relative. I bent two foot wide panels two feet in about 20 feet. Stresses were pretty low.

    Yes. I sort of assumed he meant some type of cold moulding.

    Many hands...I have a 1960 cold moulded runabout. Still solid. Five women team built it.
     
  5. Mr Efficiency
    Joined: Oct 2010
    Posts: 8,493
    Likes: 474, Points: 83, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    Foam cores will take compound curves, and even greater compound curves when heated up a little. The same can't be said about ply.
     
  6. Mike Inman
    Joined: Oct 2018
    Posts: 55
    Likes: 6, Points: 8
    Location: Jacksonville, Florida

    Mike Inman Junior Member

    I wasn't really thinking of cold molding as much as cutting away thin V-shaped pieces along the grain of the ply to allow it to behave more like a strip-plank. Using two layers of 3mm ply to form the desired hull shape, then draping with sufficient glass and epoxy to get the desired strength. The long-thin Vs of plywood would be bent into gentle simple curves, but they should come together to closely approximate a compound curve.
     
  7. JamesG123
    Joined: Mar 2015
    Posts: 655
    Likes: 75, Points: 28, Legacy Rep: 10
    Location: Columbus, GA

    JamesG123 Senior Member

    Or you could just use foam.
     
  8. Mike Inman
    Joined: Oct 2018
    Posts: 55
    Likes: 6, Points: 8
    Location: Jacksonville, Florida

    Mike Inman Junior Member

  9. JamesG123
    Joined: Mar 2015
    Posts: 655
    Likes: 75, Points: 28, Legacy Rep: 10
    Location: Columbus, GA

    JamesG123 Senior Member

    Then you should buy a used boat otherwise you're gonna owe yourself a million bucks. lol.
     
  10. Mike Inman
    Joined: Oct 2018
    Posts: 55
    Likes: 6, Points: 8
    Location: Jacksonville, Florida

    Mike Inman Junior Member

    JamesG, absolutely true about the used boat. I suppose my point was: if I can spend $10K in materials or tools which saves me 200+ hours of labor, that's starting to be a good deal. Have you seen the saga of the Tokyo Express? ( ) His personal saga ran for 8 years, and he appears to have had much more free time on his hands than I'm likely to get before I'm too feeble to do the work.
     
  11. fallguy
    Joined: Dec 2016
    Posts: 2,986
    Likes: 332, Points: 83, Legacy Rep: 10
    Location: usa

    fallguy Senior Member

    Plywood has no 'grain'. The plies are not laid grain one way. That said, tortured ply would work as you describe, but instead of torturing at a minimum; you'd have so many joins; it would be a bear to bond n fair.

    By the time you deal with that; cold moulding would have been better with no butt joins.

    For what you describe; foam.
     
  12. JamesG123
    Joined: Mar 2015
    Posts: 655
    Likes: 75, Points: 28, Legacy Rep: 10
    Location: Columbus, GA

    JamesG123 Senior Member

    Construction techniques like cold molding, "Cylinder molding" or stitch and glue aren't designed to save time as much as they are designed to save money, or rather cost of structural and fabrication materials needed since they use basic low cost materials. What you pay for is time and or labor. There is no free lunch.

    What you are asking for is infusion layup foam cored composite. Foam is ridiculously easy and fast to work with compared to ply. It is faster than anything short of stitch n' glue glass over ply. The catch is that there is a learning curve with infusion vacuum bagging and an investment in molds that will slow you down.

    There are probably a hundred threads on this topic here on BDN, enough to give you months of reading fact and (mostly) opinion, that would answer most of your question.

    Go on utubes and search for "timelapse boat building" and you will see a bunch of videos of builds for hulls of all manner of construction techniques.
    This is one of my favorites for foam infusion:
     
  13. Mike Inman
    Joined: Oct 2018
    Posts: 55
    Likes: 6, Points: 8
    Location: Jacksonville, Florida

    Mike Inman Junior Member

    November 2009 through January 2013... seems like a typical schedule.

    I guess I'm spoiled, I came very close to building a stich n' glue plywood dory (opted to buy a similar aluminum hull instead) and since then that's my internal reference concept of how to efficiently build a hull.

    True, but there are some very cheap "ready to sail" used boats out there in the >30' <$20K range.
     
  14. JamesG123
    Joined: Mar 2015
    Posts: 655
    Likes: 75, Points: 28, Legacy Rep: 10
    Location: Columbus, GA

    JamesG123 Senior Member

    In almost everyone's case, that is the most prudent thing to do.
     

  15. Mike Inman
    Joined: Oct 2018
    Posts: 55
    Likes: 6, Points: 8
    Location: Jacksonville, Florida

    Mike Inman Junior Member

    Of course, but to be a little argumentative, I'm looking at 3mm 3 ply Okoume - and the top layer will have a grain in one direction which does pretty strongly influence how it behaves when bent.

    Agreed, and a (simple) laser is only going to cut orthogonal to the sheet - maybe if the laser head were (at least) 4 axis it could pre-cut bevels into the sheets, reducing the effort in the bond/fair steps, but I'm not sure I've ever seen a 4+ axis laser head for cutting full size plywood sheets.

    So, my initial, hopeful, thought on using 3mm ply was to do two layers of it and overlap the joins - that would either leave butt-ends (is that really so bad when they are under glass?), or a lot of scarfing to do. In my younger days I scarfed the edge of a (single) sheet of 3/4 plywood I made into a hurricane shutter. I'm sure I did it "the hard way" with 80 grit on a belt sander, but the experience left me convinced that A) butt joins were just fine for the other 19 shutter panels, and B) scarfing is for a machine, or at least somebody else to do.

    Also in my younger days, I made a couple of cabinet boxes using resorcinol glue and varnish - needless to say, 30 years later those boxes are still holding strong, but I would assume that in a hull building application the epoxy used to attach the fiberglass would be easier to work with and sufficient to bond the plywood layers?
     
Loading...
Similar Threads
  1. Cody Lanphere
    Replies:
    2
    Views:
    545
  2. Bigfork
    Replies:
    11
    Views:
    3,862
  3. robwilk37
    Replies:
    3
    Views:
    1,038
  4. alby joy
    Replies:
    0
    Views:
    400
  5. catsketcher
    Replies:
    9
    Views:
    1,321
  6. mtumut
    Replies:
    4
    Views:
    1,196
  7. Tungsten
    Replies:
    30
    Views:
    3,403
  8. bertho
    Replies:
    9
    Views:
    4,380
  9. RonanBarbarian
    Replies:
    0
    Views:
    2,162
  10. Islander11
    Replies:
    7
    Views:
    2,205
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.