Fiberglass mold/plug

Discussion in 'Fiberglass and Composite Boat Building' started by Frog4, Oct 6, 2011.

  1. Frog4
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    Frog4 Proletariat

    Trying to wrap my head around HOW to setup a fiberglass mold/plug for a Rice Speed Nozzle.

    Any ideas on how to maintain the compound radius ID/OD?

    Thinking about using a 2 piece setup ...

    :confused:
     
  2. SamSam
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    SamSam Senior Member

    With a shape like that you would need two separate molds to make 2 pieces and then stick them together to make one nozzle. The outside mold would have to be a split mold with the split being at the hump close to the 40' mark on the drawing. The inside surface has that long straight section which looks like it has
    0% draft. Since the glass and resin will shrink as it cures, it might become a problem to get the part off the mold. That mold might need to be a two piece also with a small section fore and aft that could be taken out allowing the rest of the mold to be slightly flexed to allow part removal, or a three piece mold made that would allow part removal without mold flexing. If there is 2 or 3 degree negative draft to the inner surface, you might be able to use a one piece mold there.
    [​IMG]
     
  3. Frog4
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    Frog4 Proletariat

    thanks Sam ... was thinking along those lines last night ... I believe that drawing is from patent # 5,799,394 Method of making a marine speed nozzle ... reading the diagram descriptions, it seems as if there is 0 (zero) draft on the straight sections. In the patent he does describe 3/4 pre-fab sections for welding in steel/stainless .. maybe mold/plug built the same for fiberglass ..
     
  4. SamSam
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    SamSam Senior Member

    If you make a multi part mold, you have to make one piece with negative draft on the flanges so you can get a start taking the mold apart, so the mold doesn't get locked in the part.
     
  5. Frog4
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    wondering if a 2 part mold like this would work:

    http://www.cstsales.com/tutorials/fiberglass_mold.pdf
     
  6. tunnels

    tunnels Previous Member

    Simple !! Make it like it was origanally ,41 is one end and 23 is the other end !!
    Just make it in two bits !! why change something ats already worked to make that one !!
     
  7. Frog4
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    41 as one piece and 23 as the other half?
     
  8. Frog4
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  9. Frog4
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    i guess the trouble is how am I going to make the mold(s) so that both inside and outside is smooth ... 2 parts, 3 parts and then joining them .... arrrgh

    more research ...
     
  10. SamSam
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    SamSam Senior Member

    It's not two wings, it's a tube....


    [​IMG]
     
  11. SamSam
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    SamSam Senior Member

    Well, that is a two part mold, as far as that goes. You would need a two part mold for the outside surface, and a two or three part mold for the inside surface. The outside mold would separate either on a vertical line following the high point at 40' all the way around, like slicing a bagel, or two fore and aft separations 180 degrees apart, like cutting an O to make two C s.

    The inside mold would work in two pieces if a small fore and aft piece was taken out and the mold was flexible enough so the main mold could be "curled tighter" so to speak and then taken out of the part. If you don't have a flexible mold, it would have to be at least three parts, and one of those parts would have to have negative draft, like a reverse keystone.

    The outside mold has to come off a part, the inside mold has to come out of a part. Resin shrinkage will tend to make the inside mold hard to get out of the inside part, hence the 2 or 3 parts to it.

    It kind of depends on what you are doing as far as how many of these things you want to make. I can't see where it's worth the effort to make 1 nozzle. You have to either make a plug or have a nozzle to copy, first. Making a mold requires a good amount of time and material, etc., but making a multi-piece mold in itself is not too difficult. I splashed a 1 piece racecar hood, fender, scoops etc that ended up needing 9 separate pieces.
     
  12. Frog4
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    Frog4 Proletariat

    thanks Sam ... I'm still kicking this around ... an alternative is using similar techniques audiophile installers use to "mold" sub-woofer speaker boxes for their trunks and center console mountings ... these are usually made from single or quad kerfed plywood, sanded, painted, waxed then glassed, then both parts glassed together ... maybe I can get a sound shop around here to make the mold ...
     
  13. Frog4
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    Frog4 Proletariat

    YUP, and that is what has me stumped ...
    it has a LOT of compound radii ...
     
  14. SamSam
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    SamSam Senior Member

    Are you making one of these or a bunch?
     

  15. Frog4
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    as of right now, this is a one-off, proof-of-concept for a tug build ...
     
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