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Thread: Best density foam for mold making

  1. #1
    Senior Member nicktruman's Avatar
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    Best density foam for mold making

    Hi Gurus..
    I am trying to buy some foam/polystyrene to make the mold for the cockpit to turn my Zonda from a spyder to a hard top. The factory needs to know what density foam i want. They have offered me 24 density. All sheets are 8' x 4' and the thickness I need, which is about 1 yard. Its expensive so i need to get the right stuff!

    Can you help please?
    Regards

    Nick
    Regards
    Nick

    Twin turbo V8 Zonda inspired thingy

  2. #2
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    Re: Best density foam for mold making

    Most people use urethane foam because the resin will not melt it. I think for polystyrene you will have to use epoxy resin. I would probably get the densest that they have.

  3. #3
    Senior Member Don's Avatar
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    Re: Best density foam for mold making

    If you are using polystyrene foam, get the foam that would normally be used in insulation for houses etc. Here in Canada it is pink and denser than the white foam you see people using quite often for shape making. The white is easy to work with but wil take more effort at the end to get the final shape with bondo etc.

    Both foams will need to be sealed with shellac or epoxy sealer of some kind. Then apply layers of bondo to the pieces to finish shaping and sanding smooth ready for moulding.

    Cheers
    Don
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    Senior Member nicktruman's Avatar
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    Re: Best density foam for mold making

    Thanks everyone. So I am making a male mold, i.e. I want to make a "cabin" a shade smaller than needed so when I add the fibreglass I get the right size. What thickness fibreglass should i aim at?
    Would that equate to 2 layers of 450gram and 1 layer of 220 gram CSM? plus a layer of gel coat over the top once its been rubbed down and smooth?

    My car body man will be adding other layers to the rest of the car where its too thin and where he is rubbing down the wrinkles from my early attempts at using GRP.

    I know that ideally I should make a buck, female mold etc.. But I don't have the space for a mold and i am trying to keep the cost down.

    kind regards
    Nick
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    Nick

    Twin turbo V8 Zonda inspired thingy

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    Re: Best density foam for mold making

    What is your plan? Are you going to make a foam plug and cover it with 'glass and then remove the foam? You can make a male plug by laying up a thin layer of 'glass on the foam to make a hard shell and then laying up the body over that after putting on a mold release but it will be hard to take the body off of the mold. The idea of a female mold is that it can be made in sections that can be separated after the body is laid up to get the body out of the mold. I have heard of making a female mold out of foam and then just cutting it up to get the body out. That works OK if you are just making one body.

  6. #6
    Senior Member nicktruman's Avatar
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    Re: Best density foam for mold making

    Quote Originally Posted by txbuilder
    What is your plan? Are you going to make a foam plug and cover it with 'glass and then remove the foam? You can make a male plug by laying up a thin layer of 'glass on the foam to make a hard shell and then laying up the body over that after putting on a mold release but it will be hard to take the body off of the mold. The idea of a female mold is that it can be made in sections that can be separated after the body is laid up to get the body out of the mold. I have heard of making a female mold out of foam and then just cutting it up to get the body out. That works OK if you are just making one body.
    The idea was to make a foam plug, lay the glass over that, and pulling it out afterwards. I know its hard to remove the foam as i have done it before. I am only making one car, and never agaiN!
    What thickness should i go for with the GRP, 1.5 oz or 450 gram csm is about 1mm (I think) Would 1/8th inch be too thin for a cockpit, or cabin roof? or should I aim for thicker. I dont want it too heavy, but equally i dont want it to sag or lose shape.

    Cheers
    Nick
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    Nick

    Twin turbo V8 Zonda inspired thingy

  7. #7
    Senior Member Don's Avatar
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    Re: Best density foam for mold making

    Nick;

    In my experience, the shape and location of the parts will make a difference to how think you make your parts.

    For an interior, 2-3 layers of 1.5 oz glass mat and resin will be fine for items that are not handled or leaned on regularly. Items like kick panels and rear firewall panel and windshield frame pieces etc. should be good with 2-3 layers max of matt and resin. The shape of the panels also makes a difference. Flat panels would need to be a bit thicker so they don't warp or distort over time whereas complex curved pieces will have more of an ability to retian their shapes with less thickness required.

    For items like centre console and door sills and areas where you will be using these areas to lift out or drop in to the car, should have 4 layers of 1.5 oz. glass to give it more strength. The other thing to consider is larger pieces like roof panels of flatter pieces probably want to be a bit thicker as well as the panel will warp over time if it is too thin. Door panels can be the 2-3 layers as well as long as you bolt your door handles and door pulls through the panel into the metal of the door for strength. If you can only bolt the arm rest and door pulls etc. to the panel, you will need to have those pieces thicker for strength.

    I don't thing you will ever want use 1 layer of glass on any o of the areas if it is the standard 1 or 1.5 oz. cloth of matt.

    Hope this helps.
    Don
    308 Ferrari replica
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    Re: Best density foam for mold making

    I usually go for about 3/16 thickness for exterior body parts. That is usually about 4 layers of mat and 3 layers of cloth. Keep the amount of resin you use to a minimum, just enough to fully wet the material and squeegee off the excess, and it will make a stronger and lighter part.

  9. #9
    Senior Member nicktruman's Avatar
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    Re: Best density foam for mold making

    Thanks Don and All
    I feel more confident now. I am making the roof section, so it goes up the sides and across the top of the screen and back to teh engine cover. As per the Z Cinque it will have an air inlet on the roof which will feed the engine (I guess)
    I also have to make 2 side pods that sit above the fuel tanks, one of which will have the fuel filler, I need to make the 2 rear corner valances and a new rear valance as I don't like the sheet steel one I already have.

    When I made the rest of the car, I ripped he body off the mold too quickly and over the next few days it really sagged and warped in places.

    I appreciate doing it this way is more work, but I want to leave the surface of the glass as smooth as possible so that when gel coat. or flow coat is painted over it does not need that much (as my man says) "grinding down".
    Regards
    Nick
    Regards
    Nick

    Twin turbo V8 Zonda inspired thingy

  10. #10
    Senior Member Don's Avatar
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    Re: Best density foam for mold making

    Nick;

    If you really want a smooth surface to start with then you probably need to make a mould off the foam buck and then pull a part from the female mould. that is really the only way to get a good starting surface that will be smooth and lighter.

    The way you are looking to do it, you will have foam and bondo on the inside and then more bondo to smooth out the galls skin afterward to make the outside surface smooth.

    More work but the female moulds will most likely produce a better starting point for you with your requirements.

    Cheers
    Don
    308 Ferrari replica
    Prova Countach 5000QV

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