Making a mold out of Clay?

Discussion in 'Fiberglass and Composite Boat Building' started by Jeremy Clarkson, Aug 17, 2011.

  1. peter radclyffe
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    peter radclyffe Senior Member

    i must stop making bad jokes
     
  2. CDK
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    CDK retired engineer

    No, just simple ordinary clay, I've seen these guys at work.
    They have a wire frame, so the model doesn't fall apart. Clay does shrink, so cracks appear during drying, but they fill that with something they call "engobe", which is nothing but clay and water. Once the surface is perfect and dry - that may take several weeks - they spray paint it, then install head lamps, mirrors, a windscreen etc. And you'd swear it was a real car until you knock on it.
     
  3. wet feet
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    wet feet Senior Member

    We seem to have some difference of understanding about the relative qualities of the clay that comes straight from the ground and the material used in automotive styling.The automotive styling clay can be softened by warming and does not crack or dry out as there are usually waxes incorporated in the formulation.It can hold very fine detail and with the right surface preparation a very satisfactory mould can be made.The material costs a lot more than the clay you can dig from the ground and the people who have the ability to work with it to a high level of accuracy and fairness earn a fairly substantial amount.A few clues can be found at http://www.styling-clay.co.uk/styling-clay.A good modeller can produce a convincing styling model and cover the last minute changes with Dynoc film in a very short time.It will convince almost anybody that it is a real vehicle.Perhaps they do things differently in Italy.
    If you want to take the cheap route and if you have the time and talent,mineral clay or even wire and plaster will suffice for a mould.
     
  4. peter radclyffe
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    peter radclyffe Senior Member

    i dont doubt its capabilities,its the cost and time thats against it
     
  5. Steve W
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    Steve W Senior Member

    WF,thats the type of clay i was refering to in post #12, we use it in the composite industries for fillets, blending in seams, nd small temporary repairs in molds,its great stuff but not a cheap way to make a whole mold.
    Steve.
     
  6. DCockey
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    DCockey Senior Member

    Going from a clay model to a fiberglass shell by "splashing" the clay model to create a female mold has been standard practice in the auto industry for decades. Many of the experiemental and prototype cars and trucks seen at auto shows have fiberglass bodies made by the process.

    The models are not solid clay. Rather they are built over a metal and wood armature with open-cell foam providing the substructure. The clay is not more than a couple of inches thick, and usually considerably thinner. While hand sculpting is still used today to finish clay models most of the roughing out is done with a mill. If a CAD model exists of the surface then the model may be milled close enough that only smoothing of the cutter marks is needed.

    Many of the clay modelers in the auto industry have college degrees in art. The tools they use are from diverse sources, ranging from scapel-like knives to "shurforms" to wires held taut by a small frame to simple scrapers made from sheet metal. Milling is done with a 3 or 5 axis CNC mill and a coarse ball cutter.

    Clay models, both scale and full size, are used for wind tunnel testing. Most of my hands-on experience with clay models was making modifications between runs of a wind tunnel test. The results were functional but I would never make a studio modeler.

    Chavant is a major (only?) supplier of clay to the auto industry in the US, and the clay used is oil base and contains sulfer. http://www.chavant.com It is firm at room temperature though a finger nail easily makes an impression and pressure with a finge type can leave a mark. The clay can be milled and scraped at room temperature. Warm it slightly and it softens so that it much easier to move with hand pressure, and it can also be extruded when warm. My former employer used restaurant "bun warmers" to keep the clay at a working temperature. The clay is re-used though it eventually needs to have more oil added.

    It should be quite feasible to make a male pattern of a small boat or canoe as the basis for creating a female mold. First step would be build an armature and cover it with rigid open cell foam. Roughly shape the foam so that it's surface is a half inch or so inside of the desired finish surface. Then pack modeling clay over the surface so that it protrudes past the finish surface. Then trim and scrape the clay back to the desired shape, and finish with careful scrapping.

    The major advantages of clay are that it can easily be worked by hand, and it is almost as easy to add material as to remove it. So it's great for revising a shape.
     
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  7. m3mm0s rib
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    m3mm0s rib Senior Member

    Speak for construction and clay molds Can someone tell me about the amount and cost to construct a model 9m Thanks
     
  8. gonzo
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    gonzo Senior Member

    A model of what?
     
  9. gonzo
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    gonzo Senior Member

  10. m3mm0s rib
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    m3mm0s rib Senior Member

    I'm talking about model like what I do not think I construct the clay will cost less wrong;
     
  11. DCockey
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    DCockey Senior Member

    The amount of clay would depend on the surface area of the model. Multiply the surface area of the model by an average thickness of perhaps 4 cm to estimate the volume. Then multiply the volume by the density of the clay to obtain the weight/mass of clay needed.

    Cost would depend on the price the clay supplier charges. My guess is the cost for a 9 m long model would be surprisingly high compared to creating the model from foam. Clay may be best used for small parts in a situation where the clay can be reused. Also, if clay is used for a plug to make a mold, only one mold can be made and then the clay will need to be re-modeled.
     
  12. m3mm0s rib
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    m3mm0s rib Senior Member

    My friend took a quick look at some material from the spot and sent a surprise I see that prices are slightly ahead of Europe now understand why their cost is your major
     
  13. Steve W
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    Steve W Senior Member

    Most are going to use clay for a plug rather than a mold, and for this use there are many less expensive options.
    Steve.
     
  14. m3mm0s rib
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    m3mm0s rib Senior Member

    From experience I tell you that wood is probably the cheapest material construction and immediately after the polystyrene
     

  15. pistnbroke
    Joined: Jan 2009
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    Location: Noosa.Australia where god kissed the earth.

    pistnbroke I try

    the cheapest canoe mold I ever made was 4 sheets of 3m x 1m tin shed siding with a wide 1cm profile ( about 4 across the width) . scerew the 4 together to make 6 x 2 then pull the front together and screw. Put a transom in the back and screw ..external U frame to hold the centre apart ....tape over any bits you not happy with ...spray with canola oil ...glass the inside ...undo the screws..tin falls off and fit wooden edges job done ...
    Waste of time ..too heavy ..too expensive ..should have used ply stitch and glue ...still you lean dont you ( got the idea from Aborigonal Canoe buildig)
     
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