I have a little bit of experience... nothing major.
These days, the tin based solder you can buy for doing plumbing is lead free, has similar melt to lead based solder (can be melted in a pot, for instance), and has good flow. (Its intended to flow into very tiny spaces.) It is kinda pricy though, but still cheaper in bulk than actual whitemetal alloy for miniatures. It has brilliant white luster.
Just be aware that it *is* 99% tin, and that the vapor released from melting is toxic. Use a vent hood, or do this outside.
It needs a hotter temperature than normal whitemetal, which is some 60% tin, and 40% bismuth, IIRC.
A good metal pot with an actual thermostat should be able to get hot enough.
Which then brings us to mold material: to cast with solder or whitemetal, you will need a high temperature silicone rubber mold. There are many commercially available mold building compounds available for purchase, but here is what I personally would suggest, since you will probably be making 3 or 4 part molds. (Space marines, et al.)
Pay the extra for 2 part mold mix, preferably the "putty" kind. 2 part mixes, unlike RTV preparations, don't need to breathe to cure. This let's you make very thick walls in a single session, and makes for sturdier casting molds. Try to get high temp silicone if you can: it's usally sold for making novelty candy molds, on the cheap end. Try there first.
If you find that your mold material can't handle hot solder or hot whitemetal, then you can gently abrade the inside of the thick mold wall with sand paper, and apply a thin (THIN!) Layer of automotive RTV silicone gasket maker, then re-mold your plug against that, and let it cure. Red high temp gasket maker *WILL* hold up to hot 99% tin solder. I know. I've done it. It has issues in that, since it is rtv, will take FOREVER to cure if applied thickly, if at all, --and, because of how goopy and "boogery" it is, it is difficult to make molds that don't have voids. So, only get it as a last resort, and if you find you need the heat resistance it offers, only use a very thin rind of it inside a sturdier, already made mold wall.
(Rtv silicones don't "dry". They "react" with water vapor in the air, and release acetic acid, which is why it smells like vinegar. Thick applications create "rinds" that are hydrophobic, preventing more water vapor from easily getting to the center of the mass, and retarding or stopping the curing process. Rtv silicones should never be applied thickly. For thick walls, always use 2 part silicone mixes, which cure similarly to epoxy resins. They are more expensive, but worth it.)
For making the actual mold walls, get yourself some legos. These will become part of your casting kit.
For a 3 part mold, Assemble the legos into a rectangle, so that all the insides of the rectangle are smooth. Then, apply a strip of duct tape to one side of the rectangle. Make sure the rectangle is deep enough to deal with all of the mold compound.
Place the rectangle of legos with the duct tape covering up one full side of said rectangle onto a flat working surface, so that the smooth side of the duct tape is facing down on the table, the sticky side is up, and so that the rectangle now looks like a short, fat chimney.
Mix some of the 2 part mold builder. Again, try to get the silly putty like kneadable kind if you can.
Press or pour the compound into the chimney, and either jostle it gently or squish it down really good. (Depending on what you bought.) Now, spray the item with silicone mold release, and dry it with a hair dryer. If you are using the pourable mold builder, this gives the wall a little time to firm up before we put the item into it. If using the putty kind, work fast.
Once the plug has been sprayed with release and dried, press it into the mold maker, being sure not to allow any part of the item to be submerged in the compound. Eg, if the space marine has a base, and spread legs, make sure that you put him facing down into the mold maker, and that it does not cover his legs. We need to be able to get him back out of the mold later!
Wait for the mold compound to firm up more, or, if using putty type maker, work immediately-- then wet your finger, and smooth out the top of the mold making compound. Take 2 large lego bricks, and put them "knobby side" down into the mold maker, and press the knobs all the way down. This will make impressions in that part of the mold, so that it will be easier to put all the parts together again for casting, and have them all lined up. Put one brick on each part you intend to make another part to the mold on.
Cover with cling wrap, and do something else for at least 4 hours. Better still is the next day.
When that course of the mold is cured, remove the clingwrap and the 2 notch making lego bricks gently. Lightly spray the mold with mold release, then let dry.
Now, decide which part you want to mold next. Over that part, put another strip of duct tape down. This time, stand the mold up so that the part you poured/pressed the last time is now vertical, and the new strip of duct tape forms a wall, covering the bottom portion of the remaining window. Mix more medium, and pour or press into the mold. Like last time, wait a little bit, then smooth the surface, and press a lego brick into the flashing area knobby side down.
Cover with clingwrap, wait at least 4 hours.
remove cling wrap and the lego brick. Spray again with mold release, and let dry.
Reposition the mold so that the first part is facing down again, and the lego rectangle looks like a chimney again. Half the chimney should be plugged with rubber mold, and covered with duct tape. Into the remaining section, pour or press mixed compound. Cover with cling wrap, let stand at least 4 hours.
After all the parts are cured, peel the duct tape off, and carefully disassemble the lego brick chimney. You should have a rectangular "block" of mold sections, perfectly stuck together, with the plug burried deep inside.
Carefully peel the sections of the mold apart. The mold release you sprayed at each stage of molding will allow the sections to peel away from each other, and off the plug. Remove the plug, and put it away.
Cut sprue holes (fill and vent) into the mold sections, so that the hot metal can flow into the mold when you cast. You will need an agitator of some kind if you want really fine details in the casting, otherwise the metal will not flow well. Professional casters use a "spincaster", which basically centrifuges the metal into the mold. Poor people like us can make do with an orbital vibrating sander that has been stripped of it's sand paper, and covered with double stick tape, put in a retainer frame.
When you want to cast, clamp the rubber sections of mold together with something like plumber's strapping, or with some other good quality clamp that can effective hold all 3 sections together, then stick it to the double stick tape with the fill sprue holes facing up. Turn on the sander to agitate the mold, then slowly and gently fill the mold with the metal.
Wait a good 5 minutes after pouring to turn off the sander, unclamp, and unmold.
With any luck, it should have molded properly, and be a good cast. If not, plunk it back into the melting pot and try again. "Flashing", where metal seeps between the mold sections, is normal. Cut that off with a good hobby knife.
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Topic: Miniature Casting (Read 4133 times)