# Making a mold



## Strider (Jun 29, 2009)

Hello again!
I have a question. What is the most suitable material for a mold? Made from metal? Plaster? Clay? These are more or less reusable (maybe not clay), are there any other techniques of making a shape in the mold...like in first sand mold. How do make the shape of object inside sand, like in this case


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## 4metals (Jun 29, 2009)

The easiest way to make a mold is out of a block of graphite, it is easy to carve with an tool that is the equivalent of a flat bottom drill using a drill press.

The method in your picture is (I believe) using the lost wax method. Basically a shape is carved out of wax (soft and easy to carve) and cast into the concrete like vestment to make solid block with the shape of the wax inside. Make sure one side touches the outside of the cast block for the wax to come out and the metal to go into. 

When the vestment cures the entire block is heated in an oven with the hole on the bottom for the wax to melt and drain out, leaving a void inside the vestment exactly the shape of your wax carving. 

Now the molten metal is poured into the mold as in the picture. If repeated castings are required the mold is made to split in half to remove the piece cast, otherwise it is just broken open.

Maybe a caster of jewelry can give a more detailed description.


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## g_axelsson (Jun 29, 2009)

What do you want to cast?

The best mold is depending on what you want to do. Size, material, surface finish shrinkage... there are a lot of factors that goes into type and choice of material for the mold.

The mold on the picture looks like a sand mold and the metal looks like tin or maybe zinc.
A sand mold is made in two pieces, packing the sand around a template, split in two pieces and the template is removed creating a void for the metal.

If you are interested in metal casting and want to know more I recommend a site I think is called backyardcasting. Google is your friend here. They have a lot of information of different techniques.

/Göran


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## Anonymous (Jun 29, 2009)

Casting with green or oil based sand the pattern can be anything form the original part, wood, plaster, auto body filler or a combination of materials. A favorite of mine is RTV ( Room Temperature Vulcanizing Rubbers ).

On the original part you will see a seam, this is called the parting line. Make a box with two halves pinnned so they will join in the same location when joined, fill the bottom half of the box with modeling clay then insert your part to the parting line or as near as you can, trim any excess clay away for the parting line.

Affix the top half of the box onto the pins, seal the cracks with modeling clay, using a rounded dowel ( acorn nut ) make some insertions into the clay around the part, you do not need more than four insertions. 

Spray on some mold release onto the part, mix up the RTV, keeping bubbles to a minimum, then pour in the RTV to the top half of the box let this cure, once this has cured pull the bottom half of the box off and remove all the clay.

Using RTV on large parts the air bubbles come to the top and do not create a problem, to remove the bubbles you have to vacuum the container of freshly mixed RTV. Another method is to insert the box inside an old pressure cooker and pressurize to 15 lbs this will compress the bubbles.

Put the box together sealing the cracks with clay then repeat, spray mold release, pour enough RTV to fill the box, once cured remove the part, now you have an exact replica inside this cavity which you fill with wax. The wax copy is set inside plaster, the wax melted out then replaced with molten metal of your choice.

Now that both halves are poured and cured with the part removed, you will see that you now have a male/female registration marks where you made the insertions into the clay. These registration marks are important in aligning the mold halves back together.

The eagle pattern in the attached file, was made first in RTV, using one half of the RTV mold poured in auto body filler then attached the half part to wood to finish the bookend pattern.

Sand Casting.

In this first link you will see that I have altered the fishing weight mold using auto body filler, the original part was die cast.
http://i235.photobucket.com/albums/ee193/gustavus1_photos/Foundry_1/three.jpg

The first half of the foundry box has been tamped with an oil base sand, the white powder is called parting powder.
http://i235.photobucket.com/albums/ee193/gustavus1_photos/Foundry_1/five.jpg

Patterns removed waiting to have the flask put together for receiving the molten metal
http://i235.photobucket.com/albums/ee193/gustavus1_photos/Foundry_1/six.jpg

Metal poured and cooled, parts still attached waiting to be cut free and finished.
http://i235.photobucket.com/albums/ee193/gustavus1_photos/Foundry_1/eight.jpg

The spoon is used to cut gates, the straw to blow loose sand from the mold cavities, the knife to ward of the curious.
http://i235.photobucket.com/albums/ee193/gustavus1_photos/Foundry_1/nine.jpg

When you hobby pays returns you can buy toys to make the job easier, my pneumatic tamper.
http://i235.photobucket.com/albums/ee193/gustavus1_photos/Foundry_1/four.jpg


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## Strider (Jun 29, 2009)

I would like to cast aluminum, I have plenty of it...I wouldn't want anything complicated, just maybe a edelweiss flower, or something else...so basically I need to make a wax model out of it, then put into wet sand...or should i make a clay model, let it dry and then make another clay mold? I could just carve it fromm wood and then into clay or sand.

I heard something about lost foam, that you just pour metal inside the mold, with the foam inside, and it evaporates? why can't you do that with wax?

What is that eagle representing?


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## jimdoc (Jun 29, 2009)

Check this site;
http://backyardmetalcasting.com/


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## Anonymous (Jun 29, 2009)

The eagle is the Case Tractor mascot, here is the full story of Abe from Yesterdays Tractors http://www.ytmag.com/articles/artint51.htm

Aluminum is an easy metal to cast, bu cautioned using green sand that has a moisture content. To much water can cause steam explosions when the over moist sand comes into contact with molten metal. Be sure to wear safety gear and goggles.

Avoid using extruded aluminum ( window and door frames ), pop and beer cans. Use only cast aluminum such as that used for engine cylinder heads and blocks, cast automotive rimes, hydraulic pumps.


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## Strider (Jun 29, 2009)

I saw molted metal pop like volcano...wouldn't wanna get a drop of that on my skin.

I have 3-4 aluminum plates, used to cool down laptops, I guess that it is pure


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## Lou (Jul 1, 2009)

4metals,

That was a greensand casting--bentonite, water, and sand with perhaps some other additives like hardwood flour to improve peel. Lost wax casting is as you simply described, and something I love to do!! 


Neat work Gustavus, I like you more and more!! I use petrobond for my aluminum and light bronze and brass. Don't do much cast iron since my sand is fine lacks the porosity for hotter casts.


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## Anonymous (Jul 2, 2009)

Thanks for your kind words Lou. I have been using Petrobond from the beginning of my hobby for most of my castings. I have been experimenting with lost wax using a commercial plaster formula that you beat a lot of air into, it's lighter than popcorn when dry.

Last year I played with Expandable Polystyrene Beads used in commercial foundry's for the lost foam process. The beads have a bit of butane inside which causes them to expand inside the pattern mold when steamed. The problem I experienced was I did not have enough steam ports in the mold and I could not achieve a fully expanded pattern.

FYI: The duck and goose decoy guys use a similar bead only courser, they boil the mold in hot water to expand the beads. The polystyrene beads used in decoys have a different chemical composition and do not burn out cleanly when the metal is poured in.

I have an ongoing love affair with the Ford flathead V8, and would like to cast some Tri-Power intake manifolds in aluminum. There is a core sand available that you cure with CO2.

These blokes from Australia have inspired me in a big way, they have made the patterns to cast a Austin Healey Alloy Engine.
http://www.dmdaustralia.com.au/block.html


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## Strider (Jul 3, 2009)

very cool...I saw a guy making an aluminum skull with lost foam technique...very good it turned out...

I found a clay technique, with two cups, the clay is reusable, it is, I guess, used by gold and silversmiths...just the thing I was looking for, small but important


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