Efficient way to fabricate a mold ?

Discussion in 'Fiberglass and Composite Boat Building' started by antonkov, Apr 12, 2020.

  1. KD8NPB
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    KD8NPB Junior Member

    Large radii make it easy, as well as the correct tools. Dynabrade makes a variety of specialty tools for sanding nooks and crannies. Dynabrade #58010 is a big timesaver. #58485 is also quite useful for tooling work.
     
  2. Dejay
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    Dejay Senior Newbie

    Are there large CNC machines that can sand and polish a mold or plug? I figure if you can machine the foam you should also be able to sand and polish the surface with the right tools.
     
  3. antonkov
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    antonkov Junior Member

    If finishing the surface on a one-off mould or plug, would it be any easier to get the shape and surface with the mould/plug and work out the finish on the final part? One way or another the surface needs to be finished, only on the foam it requires the extra step of glassing while on the final part you already have the hard layer to work with. Just a thought.
     
  4. KD8NPB
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    KD8NPB Junior Member

    Usually P400 is the stopping point. As said, for cheap molds or one offs, going higher doesn’t make sense since there will be imperfections to fix anyways
     
  5. Rumars
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    Rumars Senior Member

    What do you do on the finished piece, sand and polish the gelcoat? Or is this only for items to be painted?
     
  6. KD8NPB
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    KD8NPB Junior Member

    Wetsand P600, 800, 1000 then buff. As long as there’s about 24 mils of gelcoat on the piece, there is enough to lightly sand on. While this is being done, it will also remove moderate heat distortion and imperfections.
     
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  7. ondarvr
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    ondarvr Senior Member

    A customer recently built a 65' cat to CC specs for passenger tours.

    The cabin roof was 40'×20'

    The mold was Plywood with a crown.

    Sprayed on Duratec High Build primer in the morning.

    Sanded with a custom built floor sander thing in the afternoon.

    Sprayed Duratec black high gloss top coat the next morning.

    Didn't touch that surface, then started applying mold release the next day.

    Infused the part two days later.

    Since the part was being painted it didn't matter if the surface was perfect.

    They were going to build 3-4 of these cats so the molds only needed to hold up for a limited time.

    The hull molds were built in a similar manor, only with cedar strips with primer on top.

    For one offs, or limited use some people sand and polish the primer. For this project it was easier to sand the primer and use the high gloss top coat, less sanding on the primer, and no buffing and polishing
     
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  8. KD8NPB
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    KD8NPB Junior Member

    that’s a new one.

    Pressure pot? What tip size and reducer solvent percentage?
     
  9. ondarvr
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    ondarvr Senior Member

    Yes to the pressure pot, not sure on the tip size. For this part it was a large tip though.

    Used the Duratec gel time extender.

    I don't think they thinned the top coat, but sometimes I do thin it by about 3% with the Duratec reducer.

    It was the polyester top coat.
     
  10. ondarvr
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    ondarvr Senior Member

    An airless gun can be used, tip size for large parts is an 18-40*
     
  11. KD8NPB
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    KD8NPB Junior Member

    I’ll give it a shot on my next one. I finally upgraded from a no-name... bought a surplus lot from a closed factory, and got 3 Devilbiss PP+JGA504 setups and a bunch of misc Binks guns. First time I’ve had a brand name touch up gun!

    There’s a 1.8mm tip in there, I’ll give it a shot with that and see how I like the profile. I mainly build molds for stuff under 500 sq ft surface area.
     
  12. ondarvr
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    ondarvr Senior Member

    The 1.8 will spray the top coat fairly well, but a 2.5mm or even a 3 will make quick work of it.

    This all depends on the shape of the part. Big flat or easy to spray surfaces get the larger tip.

    The large tip makes the primers go on much better too.
     
  13. ondarvr
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    ondarvr Senior Member

    If you haven't used the gel time extender try it.

    It will about double the pot life on the entire line of products. Its doesn't affect the cure time of the sprayed material as much as the pot life.
     
  14. ondarvr
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    ondarvr Senior Member

    Theoretically yes, but I don't know of it being done.

    The cost would be very high to set it all up.
     

  15. waikikin
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    waikikin Senior Member

    It's quite a while since I've used Duratec but found it really terrific.. & the main issue was pot life so used two guns and a helper when available to wash gun between each pot- thinking back then we were getting about 10-12 minutes to be safe with 700 gram batches. Only issue I had one was a late in day spray and came in next morning to sticky product, a mate helped tent it and cooked it up with a few cheap fan heaters and was happy by lunch. Great thing is the black gloss really proves the surface and you can rescue little issues by cutting back to the grey in spots if required and it still polishes up great- Duratec is up there with sliced bread as a top product.
    Jeff
     
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