Lost Wax Casting
There is always something else to try. I needed to make an marine exhaust manifold for my diesel engine and after looking at other manifolds with all of their curved shapes, it seamed like wax was the way to go. Normal paraffin wax available from the hobby store is not suited for casting because it was not hard enough to easily cut or machine. The answer to soft spongy wax is to purchase Machinable Wax. Machineable wax can also be used for temporarily potting electronics to make them waterproof. You can see how to make Machineable Wax on "Water Proofing" page.
(1) To make the wax pipe for the manifold I leveled a sheet of aluminum and clamped some scraps of aluminum to form 3/8 inches walls. A large cookie sheet or baking pan would have done equally as well. I then greased it up with either dish soap or petroleum jelly. Both of these worked well as release agents. You need to grease the PCV pipe that will be used to form the wax pipe too.
(2) Be careful not to get the mixture too hot. I finally got use my fire extinguisher when the mixture burst into flames as I was pouring it out. Wish I had that photo! Once on the aluminum it quickly cools enough to be handled with gloves. The edges can be cut free with a knife and the sheet pulled free.
(3) With help from my lovely assistant we wrapped it around a PVC pipe, trimmed it to fix, and wrapped it up with masking tape so it could cool. Once it has cooled the seam down the length of the pipe can be fused together with a hot knife blade.
(4) Shaping wax into a pipe can be done by cutting apart a PVC pipe, making a plaster cast, casting the "Plastic-Wax" and then fusing the part together. So it could be done to make a manifold, but it was taking way too long and I could not get the wax thickness as uniform as I would have liked. Some places were 3/16 of an inch and others were 1/4 inch. So I abounded the lost wax approach and redesigned my manifold to try it with lost foam.
While I was playing with my batch of machinable wax I cast a 4 inch cylinder and turned it down to make patterns for casting. (5) The machinable wax turns beautifully in a lathe. It acts just like aluminum, except the tool never needs sharpening. (6) The wax can also be cut freehand with something a simple as a knife. Care must be taken to only use light pressure as the chuck has a tenuous grip on the part. Wrapping the cylinder with duct tape helps give the jaws more gripping power.
(7) (8) I tested the wax parts in a split plaster mold. I read somewhere that Pam or other non-stick cooking spray makes a good release agent so I gave it a try. It's not true! The plaster stuck to wax like glue. Petroleum jelly would have been much better. However once I dried the mold for a few days it did split open cleanly and release the wax parts.
(9) However I used paraffin wax for the spur and runners and when I dried the plaster, I melted the paraffin wax and it soaked into the plaster. If I had fired the plaster I would have burned the wax out completely but instead I tried casting the aluminum as it was. The result was that the alumimn burned off the pariffin causing the plaster to crack, aluminum to blow back out of the spur, and large voids to form in the casting. The would have worked had I either burned out the paraffin or had I made the sprues and runners from machineable wax.
(10) Turns out this machineable wax stuff is great for decorating pumpkins too. We make a plaster cast of Randi's face while she bit into an orange half. Then make a plastic wax casting from the plaster, glued it into a pumpkin and painted it orange. The high melting point of the machineable wax kept the candle from melting the casting.