low-temp melt castings basics

If the pieces are small and you want to try something really retro you can make mold cavities in cuttlefish bone after sanding the flat side of the pieces of bone smooth. You can carve the mold cavity or if you have a pattern piece just squeeze or pound it into the bone.

Here's a link:

I had an old timer jeweler show this to me when I was a kid. He demonstrated the technique by casting a pair of silver ear rings.

It might just satisfy your needs, and the cuttlefish bone IS still available:

Or, try your local pet shop. IIRC parrots and similar birds like to chew on it.

HTH,

Jeff

Hmm, that's definitely low tech! Thanks for the idea--I'll check the pet shop, but I think I need bigger pieces than I've seen in this material. I'm thinking of medallions about 2" to 2-1/2 inches in diameter.

k

Wood will work but you indeed have the problem with the tree sap. That can be cured by putting the mold in an oven and cooking it for a while to get the moisture out of the wood. Another is to use plaster or pour stone. This also needs to have the moisture cooked out of it before usage or you will have shattered molds. Note that plaster will degrade with high temps as the water is driven out of the chemical bond with the plaster itself.

-- Why isn't there an Ozone Hole at the NORTH Pole?

Go to Home Depot and get some casting plaster. You will need to heat it to drive the moisture out. Not just the non-bound water, but also the water that caused the plaster to set. This makes it weak. So you might try putting the piece on top of some waxed paper , then brushing plaster on it so you don't have air bubbles on the surface of your piece. Then put some chicken wire over the plaster and add more plaster. Let all that set. Then turn over and remove your pattern. Heat to about 400 degrees F ( I am guessing at the temp ) and then puor the metal while the mold is still hot.

You might also try buying some silicon rubber caulking compound while you are at Home Depot. It ought to work for one or two pieces. They make silicon rubber that is more heat resistant, but I am not sure where you would find it.

Dan

Art supply store should have the soapstone. A flea market might also (bed-warming stones, used griddles), as might a kitchen supply store (griddles, but not cheap). Ideally, find a broken soapstone stove in a junkyard.

Toss your wood mold in an oven for a while, or just do a few pours in it and remelt them to get the surface moisture out.

There may be a problem with your sand-casting technique or sand mix if it's "distorting when you pour in the metal"

Here a web page with some links on making a backyard furnace and some links to a bad casting and a good casting pour and her mistakes and the fixes.

Jack

Silicone molds may be suitable for this, although a bit much for just one-sided castings.

Plaster, cast around a greased pattern and baked in the oven (at 500°F for an hour or three) will hold up to all white metals. Better still, if your mold fails, you can grind it up and viola, Plaster of Paris ready to use again!

Wood will only work for solder (basically pewter), the cellulose and etc. decomposes (burns) much above 400 or 500°F, releasing gas.

What was wrong with your sand casting? Sand, properly bonded and tempered, will do anything from mercury (heh, well, if you cooled your mold with dry ice first) to steel and beyond. If it can be melted and poured, chances are it's been put in a sand mold of some sort at some time.

Greensand can be made very simply from sand with a little clay and water to make it sticky, if you don't know how it should feel it will take a lot of adjustment to get the right mixture but it's the simplest, easiest to use, and oldest (i.e. ancient) route.

Silicones are available which withstand up to 800°F, these are a bit expensive; a cooler-rated one can be used, although you get shorter life out of it.

Tim

-- "California is the breakfast state: fruits, nuts and flakes." Website:

Good ideas from lots of people--thanks.

To answer a few questions, the sand probably didn't work because of my technique, as was suggested (I was pouring directly into the mold, when I should have probably made a trough to let the metal run into the mold instead of splashing down). But since I was pressing a clay model into the sand and it broke on the first try (the disk had cupped because of uneven drying), I was looking for something a bit more sustainable in terms of mass production. Maybe I'll carve a model from wood and use it to press into the sand for another go.

The wood mold did get better after I dried it in the oven, and repetition was showing improvement, but also the wood was burning more each time, so again mass production was not looking promising.

I saw a piece of soapstone at one art supply (out of many visited) but only a very large hunk, and more than I was hoping to spend (as always, I should probably just get real and face the fact that I'll have to spend to get good results).

It was suggested to me that plain plaster would not cut it--maybe I should have tried it, hell it's cheap.

Another question re: soapstone: Just how easy is it to work this stuff? If I buy the big chunk, can I chisel off nice, clean faces, or can I cut it with a saw (hacksaw or other)? I'd like to have at least one flat side, preferably two, to make it easy to have a level mold to pour into. I realize the point is that this stuf is soft and easy to carve, but how soft is soft when we're talking stone? I'm used to wood, but haven't tried the hard stuff.

Thanks again, and please keep the advice coming--if nothing else, it's making me feel less foolish for my early failures.

k

some more links to some home foundry sites

links are at the bottom of this page(2nd section up from the bottom)

Take a look at RTV silicone molds. For small projects, Micro-Mark carries a good line of supplies.

Perhaps more to the point, they also carry a couple of excellent books on the process. From your description of your experiences, I'd say what you need now is a good book.

--RC

I used to cast pewter in 2 part silicone also. Works well. Ney smelting and refining in NY used to have the best prices for pewter. Karl

Contact a dental supply house and buy some investment for casting. It mixes up like Plaster of Paris, but will stand very high temps. The rubber material, wax also works, is mainly to make a master mold to pour the investment into. This is what is used to cast gold crowns and dental bridges. It isn't all that expensive, although I haven't bought any for over 20 years. Bugs

For mass-, but still low-tech, production, you can use vulcanised rubber moulds yourself. I think Rio Grande have the supplies needed. You make your master, sandwich it in rubber slabs, squeeze and heat to vulcanise, then slice it open and cut sprues and runners . This is good for any of the low-melting point white metal alloys up to pewter, and will give several hundred good castings before "dying". Mike in BC

For sandcasting, you don't put the piece into the sand but rather put the sand into the mold with the piece on the bottom. Then pack the sand well and you should be set. Splashing the metal in does tend to destroy the mold rather rapidly as the metal is rather heavy and erodes where it hits. If you have to splash, use a thin stream and don't allow a large drop of the metal.

-- Why isn't there an Ozone Hole at the NORTH Pole?

Plain plaster will work! You can buy casting plaster at Home Depot in

25 lb bags.

Soapstone is easy to work, but dulls tools fairly rapidly. The local highschool art classes use wood working tools to do scuptures out of soapstone. Not as well known is the fact that you can use soapstone powder somewhat like powdered metal. Mold it and compress it, then sinter it. It is how the better vacuum tube sockets were made.

Dan

Hey, that's cool. How much pressure to compress and how much heat to sinter, would you think? In other words, do you think it's something that an HSM could do?

Bob

Good to know, Thanks!

I got my plaster today, so I'll give it a try and if it doesn't turn out well I'll go buy the big hunk o' soapstone.

k