How to Make the Mini Metal Foundry

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About: Random Weekend Projects

How to make a simple backyard foundry for less than $20, for melting pop cans, and casting aluminum.

Step 1: Watch the Video

WARNING: Charcoal foundries can reach temperatures in excess of 1,000ºC, which is well above the melting point of hobbyists. This project should only be attempted with adequate knowledge and training, proper protective safety gear, and in a fire resistant area with adequate ventilation. The sparks flying from the foundry can ignite fires, and the fumes from burning dross can be toxic. Use caution and common sense. Use of this video content is at your own risk.

Step 2: The Mini Metal Foundry

In this project you’ll see how to use equal parts of sand and plaster, to make a simple backyard foundry, that’s powerful enough to melt scrap metal in seconds, but still pleasant enough keep around for decoration.

Step 3: Things You'll Need

Start this project with a big bag of play sand, and some plaster of paris. Both of which you can find at your local hardware store, for under $20.

You’ll also need a 10 quart steel bucket, and a tablecloth to cover anything important, because chances are this is going to get a bit messy.

A 2.5 quart bucket can be used for measuring the ingredients, but it also serves a more important purpose that you’ll see in just a second.

The recipe for this makeshift refractory lining, is 1-3/4 buckets full (21 cups) of plaster of paris, 1-3/4 buckets full (21 cups) of sand. And 1-1/4 buckets, filled (15 cups) with water.

Step 4: Refractory Mix

The moment the water touches the dry mix, the clock starts ticking. You’ve only got about 15 minutes before it all hardens up. So get busy mixing everything together.

It’s really important to get all the dry powder wet, and work out any lumps as quickly as possible.

After mixing for a couple of minutes, it should be fairly runny, and roughly all the same color. When you’re convinced there aren’t any clumps of powder left in the bucket, the refractory mix is ready for pouring.

Carefully transfer it to the steel bucket as slowly as practical, to minimize the splattering. There should be just enough fluid to fill the bucket about 3” from the top. Now bring back the plastic measuring bucket, and use it to form the center of the foundry.

Fill the bucket with water, to give it a bit of weight, but anything like sand or rocks will work as well. As you push the bucket into the center, the mixture rises upward, but it won’t spill out.

Before the mix is starts to firm up, try working the bucket up and down a few times, to help level it before it sets. Now hold still for 2 to 3 minutes. This will give the plaster just enough time to harden, so the bucket stays in place, even when you let go.

Time for a little cleanup.

Step 5: Clean Up

Everything will still need about an hour to really harden up, but the plaster’s still soft enough that you can clean and shape it to look really good. And while you’re here we may as well wipe the bucket down as well.

Dampen a rag and gently drag it around the top, the surface cleans up pretty nicely, and gets a cool texture in the process. When it looks the way you want it too, simply leave it for about an hour.

While you’re waiting, turn an old steel fire extinguisher, into a custom crucible.

Step 6: Making the Crucible

You can tell it’s made from steel because a magnet sticks to it. And magnets won’t do that to aluminum.

Depressurize the tank and unscrew the valve from the top, to make it safe and easy to cut in half with a hacksaw. Which should happen in less than a minute.

The bottom part of the extinguisher is what you want for the crucible, because it’s basically a steel cup 3” in diameter, and 5” tall. That’s going to be perfect for your custom backyard foundry.

Step 7: Making It Professional

At this point, the plaster should be pretty well set, so dump the water from the bucket, then use something like a pair of channel locks, to grip one edge of the pail, and pull gently toward the center.

Grip it with both hands and give it a bit of a twist, you can see the whole bucket pops loose, and pulls right out. This just created an amazingly smooth surface, which gives this makeshift foundry, a surprisingly professional look.

The only features you are missing now, are an air supply port, and a lid, so make those next.

Step 8: Lid & Supply Port

A 1-3/8” (35mm) hole saw is the perfect size for accommodating this 1” steel tubing, and if you center the metal cutting blade with the top line on the bucket, you can carefully begin cutting through the metal wall.

Once through the metal, it’s easy to burrow down at about a 30º angle because the plaster hasn’t fully cured, and cuts away like butter.

Now you have a tight, downward sloping hole, that the blower tube fits perfectly into, and it’s strategically placed, a few inches up from the bottom. This way, if a crucible fails, and dumps molten metal into the foundry, it will stay in the foundry, instead of dangerously flowing out of the pipe.

The blower tube is really easy to make. Start with a 1” steel pipe. This is the “business end” that will sit next to the hot coals in the foundry. You’re also going to need a 1" PVC coupling (Slip x FIPT), as well as some 1” PVC pipe.

You can see the threads on one half the coupling screw onto the steel pipe, and the slip adaptor on the other end, simply pushes onto the PVC tube. It’s that easy.

Now go one step further and make a lid to help retain the heat.

Get a couple of 4” U-bolts from the hardware store and stand them upright in a 5 quart, bigmouth bucket, filled with a half-measure of our insulating mix. (10 cups plaster, 10 cups sand ,7 cups water).

After an hour, the plaster should have set, and the whole thing pops free from the bucket, giving you a nice little custom lid for the foundry.

It still needs a vent hole for relieving pressure buildup, and you could just form one when you’re casting it, or you could try drilling one with a 3” hole cutting saw like this.

With the hole in the center, you can see you end up with a nice thick lid, that kind of looks like a giant white donut. This design works great for venting pressure, and gives you the option to melt metal as well, without even having to take the lid off the furnace.

Step 9: Finishing Touches and First Firing

Pick up a can of “Burnished Amber” spray paint, and give the foundry a couple of coatings to make it look a little more attractive.

When you get it fired up, the mini foundry gets so hot on the inside, that it will melt soda cans within seconds and fill a crucible with liquid aluminum. Look for how to do that, in another project video.

With this homemade furnace, you have the power to liquify aluminum in the backyard, and cast just about any object you can think of.

The best part is, when you’re not melting scrap metals, rather than taking up space and looking terrible, you can drop in a plant, and instantly transform it, into fashionable home decor.

Step 10: How to Melt Soda Cans

With this transforming “Flowerpot Foundry”, there’s certainly “more than meets the eye”. And by the way, if you run out of soda cans to melt, you could try using it as a blacksmithing forge, or even a bbq, for summertime grilling. After all, it is fueled by charcoal briquettes.

Well now you know, how to use commonly available materials, to build the mini metal foundry. Powerful enough to melt metal in seconds, but still pleasant enough keep around for decoration.

Well that’s it for now. If you liked this project, perhaps you’ll like some of my others. Check them out at www.thekingofrandom.com.

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385 Discussions

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GarthKH

Question 4 weeks ago

I am wanting to cast aluminium disks and plates to be used in lathe projects and this foundry looks simple to build and use. I see various comments on the internet not to use sand and plaster of paris but rather use perlite recipes etc. They are saying that the refactory material of sand and POP cracks and breaks up. Can users here tell me how their foundries are standing up to use?

Can anyone who has built this project tell me what is the max temp they have achieved? Looking for foundry to heat up and melt copper. Any ideas would help. Thank you

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Zaachariajack.hayes.35574

Reply 5 months ago

We had a foundry using propane and a fan; we were able to cast propeller bronze but when we dropped a copper penny into it, the penny stayed a penny floating in the bronze. I currently work with warm glass which has a working point similar to copper; I use a special kiln designed to be used in a microwave oven - I am going to test it for copper (I have about 500 copper pennies all 'wheat-straw' worth face value). If I remember, I will post results here.

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PhysicistChrisZaacharia

Reply 4 months ago

Penny composition have changed a lot of the years. There is awhile (but I don't remember the years) that pennies were nickel plated, which has as much higher melting point (like 2600 F ish rather than 1900 F ish for copper ) so it is possible to get a melted core with a soft nickle skin. It will stay in shape and form until it is moved around a bit, and then it will collapse and melt.

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Jack A LopezTimothy Reilly

Answer 5 months ago

I dunno. Maker Casual?
;-P

Gloves are a good idea, since you will have to manipulate things that are hot.

Safety glasses are a good idea too, since this thing might occasionally be throwing hot sparks.

The picture in Step 9, the picture of Grant pouring molten aluminum into the sand mold, gives us some clues also. I mean, if you look at that picture, paying attention to the clothing he is wearing.

Also you can watch the video, linked in Step 10, again paying attention to clothing.

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Timothy Reilly

Question 4 months ago

could someone please tell me if I can make a mold out of a mixture of plaster of paris and sand and water?

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Timothy Reilly

Question 4 months ago

does anyone know if it is okay to use a plaster of paris, sand, and water mixture for a mold.

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DavidJ468

5 months ago

Not much info on the melted cans. I found years ago that if you melt aluminium in steel and leave it to soak - the ally absorbs metal and goes stiff and unworkable. So its should be ok in the crucible itself but not the metal container - unless you melt alvailble ally at once in the container then cast once its melted. Neat little furnace and a assume you dont have the problems with charcol / coal as with LPG gas regarding hydrogen bubbles forming in the ally when you machine it {due to water I understand}.

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code3gamingofficial01

11 months ago

If there's something that is more heat resistant and stronger than Plaster of Paris? Please let me know.

2 replies
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Zaachariacode3gamingofficial01

Reply 5 months ago

I use Cast-a-Lot to melt glass - it can be used more than once. Glass has a working point as low as 1850 F but I cast at about 2k F to get interesting convection currents - i suppose I really should do a 'structible sometime soon.

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n4mwdcode3gamingofficial01

Reply 7 months ago

Dry joint compound would be my first guess. Its also used for the slurry when making lost wax castings.

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Timothy Reilly

Question 6 months ago

what should I wear while using the foundry to melt metal?

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ClintC12

1 year ago

Does anyone know if you set the crucible on top of the coals, or just put the coals around the crucible?

1 reply
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Timothy ReillyClintC12

Reply 6 months ago

It says in the video at the end to put five coals on the bottom of the foundry then to put the crucible on them and then to surround the crucible with more coals.

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Timothy Reilly

Question 6 months ago on Step 1

is it okay if I were to use plaster of paris, sand, and water to make a mold?

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Timothy Reilly

Question 6 months ago on Step 10

what does the heat resistence of the pvc pipe have to be?