From plug to mold

Discussion in 'Fiberglass and Composite Boat Building' started by Tungsten, Mar 23, 2014.

  1. Tungsten
    Joined: Nov 2011
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    Tungsten Senior Member

    So I've built a full size model of my boat from 1/8th hard board sheets.My plan is to now make a mold of the sides so I can infuse both sides of the 1/4" foam in one shot.
    My question is how to copy the bends and twists from the plug?

    The sides are 19' long and approx. 2' high,I'm not sure how much twist and bend I'll get after there infused so if I can match my plug pretty close they'll be easier to stich to the floor.

    the plug.

    [​IMG]
     
  2. wet feet
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    wet feet Senior Member

    Before you make an expensive series of mistakes it might be extremely useful for you to build a small model of your boat and go through the manufacturing process.If you begin by producing a plug at say 1/5 scale and then paint and prepare it for moulding it will be useful knowledge for the future.You can then make a mould and lay up a hull with any laminating technique you like.Then when you feel proficient it may be time to do the full size boat.
     
  3. Tungsten
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    Tungsten Senior Member

    Thanks for your reply,as you can tell I have no experience with the terminology or building any molds.

    So far I've built a series of frames that copy the sides from the model.I was hoping there was some miracle way of doing this.
     
  4. rwatson
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    rwatson Senior Member

    As I understand your problem, you cant simply infuse the developable panels flat, because you could end up with unbendable sections.

    Thats a good safe approach.

    But the normal approach for infused core builds is to do the whole hull on a mould, not join them together after sides, bottom etc are built separately

    is there a special reason why you are doing it in sections ?


    eg
     
  5. Tungsten
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    Tungsten Senior Member

    Yes your right,the panels will not bend very easy.Infusing the perforated sides from the inside leaves me with the flat fair surface on the outside.The floor will be wet bagged on the inside.After stitching together fillet tape the inside,flip boat over .I now have completed sides so I can tape/seal too for the bottom infusion.

    At least that's the plan,I figured side molds would be much easier to construct compared to a full female mold.

    Alternatively I could stitch together the dry foam on a strong back and infuse the outside then flip and infuse in the inside much like Jorge did with his boat.
     
  6. jorgepease
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    jorgepease Senior Member

    Tungsten, I think my boat is going to turn out okay but if I had to do it over again, I would build a mold and shoot both sides at same time. You can build the mold pretty quick from mdf, it doesn't need to last you more than one boat, just brace it good. By the time you caulk and paint it several coats it should be air tight but you can always line it with plastic and tape, in the end all you will need to do is scuff it up and paint, you don't need it to pop out of the mold glossy like a gel coated boat.
     
  7. rwatson
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    rwatson Senior Member


    I was thinking more of the male mould technique - dry foam on the outside of you mould, infuse the outer part of the hull, then infusing the inside once you lift the hull off -as you mention in your last sentence.

    Your mould as it stands at the moment wont suit female moulding.

    Making separate panels to have to lay over a mould to be stitched and glued together seems like a heck of a lot more work than you need to do.

    Jorgs method of full infusion on both sides of the foam on a female mould gives me the shudders personally. You cant see what is happening under the foam, against the female mould as you infuse.

    Its true that a male mould is going to give you more finishing work, but with infusing, perhaps with peelply outer, the faring compound should get the hull into good enough shape.
     
  8. Tungsten
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    Tungsten Senior Member

    Well the separate side panels can be infused with only consumables on one side that's a plus.Infusing on a male mold uses twice the consumables and I failed at making a seal on a dry foam test piece.
    Wet bagging the inside panels on a flat bench then stitch and infuse the outside could also work,but again more consumables then infusing perforated core.

    Jorge any thoughts on infusing the 19'X 2' sides?mold would be quite high at the ends so converging resin front would be down hill almost.Maybe just a single runner down the middle with vac all around?

    Thanks for the incite guys.
     
  9. jorgepease
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    jorgepease Senior Member

    I don't understand your tool in the above picture. If your intimidated with building a full mold and you don't want to mar your nice panels with kerfs to make them easier to bend, then build a bench with the same curve as the boat ... in other words chop the tool you show in your picture above in half lenghtwise and flip it so it's like a curved table top, infuse and then easily stitch your panels together.
     
  10. groper
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    groper Senior Member

    Tungsten,

    Do as jorge indicated. Build a full female mold from MDF, or hardboard, or whatever... How long you want it to last dictates your choice...

    If a 1 off, set it up on a strongback with frames, your chosen sheeting held in place on the frames. Use epoxy fillets to make the joins from bottom to sides as you need the radius coves to prevent bridging and racetrack paths for infusion. Include a nice and wide flange around the gunnel area to lay your vac lines and bag sealant tape etc.

    Use bondo bog or similar to fill in the screw holes or nail holes and staples etc, which hold the sheeting to the frames. Sand the filled holes off and get it all ready to paint. Spray paint the entire thing with a black or other very dark colour, make sure its a very hard 2 pack type of paint - it makes it easier to see any pinholes or other blemishes that youll need to fix.

    Once its all sweet and glossy, you can setup your infusion. Its a good idea to do a test with only flow media in there first to test the vacuum integrity of your mold. Once your happy, youll need to design a fool proof infusion strategy that takes into consideration all the possible racetrack paths and flow distances etc.

    Then youll need to use a perforated core when you do your layup. It will all need to fit nicely with no large gaps or these will become racetrack paths also. I use a single part moisture cure polyurethane adhesive from a calking gun to edge glue the foam sheets together to avoid this problem. You can make patterns from the mold so that you can get the fit perfect before laying them into place in the mold.

    The rest you should already know... infuse it in a single shot using a flow media over the inside laminate. Provided you dont have any vacuum leaks, it should be a non-event.
     
  11. Tungsten
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    Tungsten Senior Member

    Jorge,since I'm not building from plans the tool was built so I have templates for the panels.Needed to work out the rocker and side height.I tried with scale models but just not the same.

    Thanks for the input groper,I;ll have to sit back and drink a few beers and let it all absorb in.
     
  12. jorgepease
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    jorgepease Senior Member

    I was in the same -boat- as the plans were for stitch and glue ply construction. I drew my own plans using the few key dimensions they gave and connected the points with a graceful curve avoiding any hard spots. I then took the dimensions off the curve at every foot to get my station dimensions. You have to do it from every perspective though, kind of a pain. If you do it this way but then you can get the tool CNC cut which is nice.

    You can also do it the way you are doing now, measure down your mockup as pictured and every 16 inches or so, cut 1/4 ply or mdf patterns to fit or even just measure. Then to get the female mold lay those patterns out on plywood or draw out your dimensions and cut them out. Remember to add the thickness of sides and room for battens to support the foam. Just make sure you are completely square and leave room on the ply for a flange.
     
  13. seby
    Joined: Dec 2014
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    seby New Member

    I am building a female mold for a 34' open fisherman ...
    I am planing the use of 3/16" hardboard - what is the best wax to use on un-painted masonite?
     
  14. gonzo
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    gonzo Senior Member

    You should read about mold structures. The pressure you will be putting on the mold will be about 10PSI. That means that a 16'x2' gets 26,880lb of total pressure. 1/4" of paneling is not going to hold its shape. They need to be really massive; a lot more than whatever you are laminating. Why do you want to infuse?
     

  15. groper
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    groper Senior Member

    Not true gonzo. I've infused stuff against sign writing foam , 1/8 in thickness, no problem. The reason is that the 14.8psi acts on both sides to cancel out.
     
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