Flexible Sheet Material for Building Molds/Plugs?

Discussion in 'Fiberglass and Composite Boat Building' started by Capt. Chris, Sep 9, 2006.

  1. Capt. Chris
    Joined: Feb 2005
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    Location: north atlantic

    Capt. Chris Junior Member

    I am now in the process of building some small molds for my Topaz 28 project. The tackle centers, bench seats and some cabinets have many inside and outside corners, which I've found out to be the most difficult to fair out. So far we cut frames on my friend's CNC, in the shape of "U"s with inside corners being of a 2" radius, but just can't find a material that can make the bends and still be rigid enough to make a smooth surface. The idea was to lay up corners and then lay up some flat panels and piece them together. The parts won't be structural and we'll awlgrip everthing to finish. If any of you Pros know of a flexible skin that can be used in this application I would appreciate it. This trial and error stuff is getting old!
    Thanks, Chris
     
  2. wet feet
    Joined: Nov 2004
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    Location: East Anglia,England

    wet feet Senior Member

    I have dealt with this sort of situation by using 0.4mm birch ply and vacuum bagging strips aroung a cylinder.If the grain of the inner and outer layers is parallel to th e axis of the strip you can build up a laminate that is sufficiently rigid and smooth enough to take a quality finish.The essential thing is to use a large enough included angle to cover all the fillet situations encountered.
    Alternatively,if there are long enough lengths with a constant angle,you can have strips of a suitable wood-basswood perhaps-machined to the shape you need.
     
  3. SamSam
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    SamSam Senior Member

    Some sort of tin should work. You could also slice PVC pipe of the right size, wax it up really well and use that. Sam
     
  4. Toot
    Joined: Jul 2006
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    Toot Senior Member

    For 2D bends, in the roofing section of hardware stores you can buy sheet metal in rolls. That stuff can be bent pretty easily.

    Also, the basswood idea is good. You'll have a little bit of core when you're finished which will be nice from a stiffness standpoint.

    Urethane foam is also good and can be heated and bent to shape.

    This next suggestion is probably heresy or something... But what about carboard? Like posterboards? Cheap cheap cheap. With the nice shiny side up and lots of wax, you can probably get it to separate from the part when you're finished. If not, you can sand it down and then add a few more layers on the back side to seal off any remaining paper fibers.
     
  5. Capt. Chris
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    Location: north atlantic

    Capt. Chris Junior Member

    Thanks for the replies!. Since my post I went back in the shop and tried a Celtex 2mm sheet, it made the bent great but ever place it came to a rib in the form it had a bump. Then I used a thin Formica, again bent good but still the same result at the ribs. I think the built up birch ply, or wood veneer is the ticket here and then thin Formica to top it. I'm hoping my tooling gelcoat will stick to this laminate. Never sprayed it on Formica before, then again if the finish is smooth enough I can just wax and pva the Formica. We plan on painting the parts to finish. Just a note... I used Duratec fairing primer in the mold instead of a gelcoat on some other flat panels that would end up painted. Pop them from the mold, then a light sand and it's ready for the primer or top coat. Worked great.
    Thanks, Chris
     
  6. fiberglass jack
    Joined: Dec 2005
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    Location: toronto

    fiberglass jack Senior Member

    what i often use for one off and custom moulds ( throw aways ) is cardboard and stick mylar on it no need to wax , sounds crazzy but works great. what u need is some stiff cardboard and or plywood a roll of cardboard the soft flexable type it comes in 100 yards rolls and a heat gun and tape, just with the plywood or stiff board cut the shape u want and then line it with the cardboard stick on the mylar tape the edges and ur ready to go. say if u wanted a tube plug just cut some plywood disks and wrap with cardboard, make sure u let the skin layer cure hard so the mould is some what sturdy
     
  7. fiberglass jack
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    fiberglass jack Senior Member

    sorry i ment a glue gun not heat gun
     
  8. fiberglass jack
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    fiberglass jack Senior Member

    also bristol board works great but give it a couple coats of wax before you put it together then just pva the sucker, always remember the kiss system when making plugs and moulds if u need some thing the size of a cornflake box us a cornflake box,
     

  9. Capt. Chris
    Joined: Feb 2005
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    Location: north atlantic

    Capt. Chris Junior Member

    Thanks Jack!,
    Just think, I've overlooked these perfectly good mold building materials all this time. I thought since it's for a "boat" it has to cost thousand of dollars for materials. Thanks for the reply,
    Chris
     
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