Lost wax style casting

Discussion in 'Finishing Techniques' started by johngomm, Mar 29, 2009.

  1. johngomm
    johngomm New Member
    Hi shapies

    I have recently used a white strong flexible model as a melt out material for a bronze casting. Caution: this is not a listed use for the material and due care should be taken to avoid inhalation of fumes. My burn-out was done in an outdoor kiln. I take a bronze casting class at the local city college making objects from wax for casting. The wax is invested in plaster and the wax is burned out in the kiln. The molten bronze is then poured into the negative space left behind.

    The white strong flexible material burned out beautifully and the cast has pretty good detail. Unfortunately I chose too thin a model and put it too high in the casting tree, which meant that the bronze cooled a little before it got there anddidnt completely fill the shape.

    If you are a caster, you'll probably be familiar with these types of problems.
    So if your considering using a piece for lost wax casting, burn out works great (take care of you lungs) and the usual casting considerations apply. I'm going to put small sprews on my model before I print for my next attempt.

    John Gomm
  2. robert
    robert New Member
    Hi John,

    Thanks for the information.

    Could you post some pictures of the results and the process? I am curious on how you did it.


  3. johngomm
    johngomm New Member
    Here's a picture of my first bronze casting attempt with WSF. The plastic melted/burned out of the plaster mold just dandy in the kiln. It is a failed piece due to the thin nature of the object and my mistakes with placement and temperature of the bronze pour. The other objects on the tree came out nicely. They were thicker pieces made from knotted nylon rope. The bronze sprews attached (crudely) are to get the bronze in from the bottom and to let the air out from the top. If I hadn't had alternative paths for the metal to go, it might have been forced through the space more effectively.

    Metal casting can't really be done without a kiln and furnace, so finding local foundry facilities is very beneficial. You could possibly cast lower melting metals with a home furnace, but lifting a crucible filled with yellow-hot molten heavy metals is not a task for the ill equipped. Especially important is thoroughly kilning the plaster mold, as any remaining moisture can flash to steam, causing the mold to explode and splash molten metal in inappropriate directions.
    Here are three fairly watchable videos about it. At the City College, we use plaster of paris/sand molds to encase our wax. Cheaper, but lower quality.

    Attached Files:

  4. BillBedford
    BillBedford New Member
    Does anyone know whether transparent detail will burn out successfully?
  5. WiKKiDWidgets
    WiKKiDWidgets New Member

    Right on! There has been much speculation around the forums about just this. Please post more pics!
  6. johngomm
    johngomm New Member
    Unfortunately, my last few models uploaded to shapeways were too hollowed out and the skin too thin. Me trying to be cheap. Anyway, they couldn't be printed, which meant I missed my pouring window and lost momentum. As soon as I get about 400 other things out the way, I'll remodel my sculptures and get them ready for casting. Don't hold your breath, sorry.

    As for Transparent Detail, I think that's a UV cured epoxy, so probably less amenable to burn out than the thermally fused WSF. Though a hot enough kiln (1000'C) will burn out most things, except clay and metals etc. Again: outdoor kiln only. You don't want to be breathing plastic fumes.

    My feeling after my attempts is that, if the price continues to fall and your model is suitable, getting it directly metal printed by shapeways is probably time and cost effecting over pouring a bronze from a WSF model, unless you do metal pouring as a hobby and are set up for it already. Even then, shapeways looks very attractive, considering all the finishing work you avoid.

    Digression: The pic here is my 3 hand built wax sculptures ready for investment tomorrow then burn out and casting next week. All the red wax is to get the bronze in and the air out. You have to grind all that off at the end. Plus you have to buy extra bronze to account for it. Typically 2x again as much as the model actually needs. Worth it for bigger stuff, but direct printing is better for small objects.
    Last edited: Jul 30, 2009
  7. johngomm
    johngomm New Member
    And here was the WSF model I tried to cast originally, tacked onto the wax for another sculpture

  8. joris
    joris New Member

    It is great to see someone explain lost wax casting to everyone!

    But, as John has warned everyone, do not try this at home! Please be very careful when burning plastics!

  9. Sabine Stonebender
    Sabine Stonebender New Member
    One option I am curious about in relation to this would be whether the stainless material could with stand a rubber mold vulcanizer so that wax versions could then be cast rather than the plastic/metal printed model.
  10. johngomm
    johngomm New Member
    You could take molds from either WSF, resin or metal prints using many molding materials.

    Most metal casters I know use either plaster of Paris or silicone to make master molds for producing multiple waxes, both take molten wax with no heat problems. A flexible material is needed to reproduce undercuts and a release agent is usually necessary, but not always.

    I'm sure you know this, but if you put gates and vents in your master mold, then your multiple waxes will be ready-gated and need minimal work before investing. Experimenting with a practice hand sculpted wax and plaster of paris the cheapest way to get to grips with the process and find out if it fits with your goals.

    Cold-casting from a master mold is also an option you might consider. Metal dust in a resin binder that cures and can take a patina like bronze. See http://www.smooth-on.com/gallery.php?galleryid=312 for a walk through the process.
  11. Sabine Stonebender
    Sabine Stonebender New Member
    Well my plan was to already have my sprues built in to the WSF model. My problem is whether that material can withstand the temperatures involved with vulcanized rubber molding (315-350 deg F) w/o breaking down. I have the press and things already for doing this type of molding so its ideal for me to have models ready to mold from go.Sorry for the lateness of my reply but i forgot to check the reply notification on the thread :blush: