Introduction: How to Make the Mini Metal Foundry

Picture of How to Make the Mini Metal Foundry

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

Picture of 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

Picture of 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

Picture of 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

Picture of 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

Picture of 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

Picture of 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

Picture of 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

Picture of 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


Archetype44 (author)2016-12-05

I made the foundry, but I could not find a 1-3/8" hole saw anywhere. I used a 1" one instead because when I found a 1-3/8" one, they were very expensive ($50-$70). I also didn't have a hair dryer lying around so I used an air pump from a queen size mattress. Will this affect the performance? The cans already don't melt well and I'm wondering if I should get a better source of air or drill another 1" hole and add a second air pump. Any thoughts on what should I do?

JonasB55 (author)Archetype442017-11-16

i assume don't melt well means they melt slow? Tons of ideas:

Are you insulated properly? Try wrapping the foundry in non flammable insulation.

Are you blowing the heat out of the foundry? The gaps in your lid, angle of the flame and most of all the airspeed from the fan.

Are you adding enough heat? The preassure of your tank and capacitry of your regulator.

bigredlevy made it! (author)2017-07-17

I have been working on this for several weeks now. AU$140 spent on making charcoal furnace, steel crucible, crucible tongs and dross scoop, pavers and sand bed (for safety in case of spill), muffin tin for casting ingots, BBQ briquettes, and fire lighters.

Furnace refractory mixture; plaster of paris, sand, water mixed in ratio 1:1:0.7 by volume. 15L galvanised bucket used as body, with 9L plastic bucket used as internal former. 2.5kg plaster of paris required for body, and an additional 1kg for the lid. Lid was reinforced with steel wire tangled in a doughnut shape and pressed into mixture.

Steel crucible made from 80x80mm square tube 3mm wall thickness. 3mm plate welded to base with double seam. 3mm lip welded to top of crucible to grip with tongs, and provide pouring spout.

Crucible tongs made from sections of 80x80mm square tube, 3mm plate, and 12mm re-bar.

Dross scoop made from half section of 30mm pipe welded to 12mm re-bar.

First melt yielded 1.7kg aluminium cast in ingots, with one test piece cast as polystyrene lost foam casting. Raw material was 2 full garbage bags of aluminium cans (unsure of exact number or starting weight).

LloydR13 (author)bigredlevy2017-11-04

Gday mate, Im assuming you'd be an Aussie or Kiwi with ref to Bunnings and mm. Well done and on your setup, pretty close to old mate King of Random? Im not far from making my setup but going with gas and using steel wool (stainless) to reinforce the structure. Nice work on the crucible and tongs, are you a rod burner by trade? Also, you mention poop scoop, got and piccies of that? Cheers.

ClintC12 made it! (author)2017-09-16

So I built this, and made a crucible out of schedule 40 3" pipe with a
1/4" metal plate bottom. First firing to melt lead, I melted the lead,
but also melted a whole in the side of the nearly 1/4" metal pipe! I
know the the fire is too hot, any advice on how to regulate the temp

ClintC12 (author)2017-09-12

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

TheMrCode (author)2017-03-30

whered u get the buckets

TheMrCode (author)TheMrCode2017-03-30

so i looked it up and im finding galvanized steel is that ok to use?

1piercedguy (author)TheMrCode2017-09-11

No galvanized steel puts off toxic fumes when heated

PatrickE65 (author)TheMrCode2017-04-23

galvanized steel lets off toxic fumes when hot enough

TheMrCode (author)PatrickE652017-04-24


BunnyN2 (author)2017-01-31

Did you use anything to blow air in the air supply pipe?

HarmonyC2 (author)BunnyN22017-07-29

in his later videos he shows a weird setup of hooking up a blowdryer to it

mizvixi (author)HarmonyC22017-09-10

I had instructions for making a foundry out of a clay flowerpot that used an old dishwasher blower motor to blow air. I was thinking of using a shop vac or a good old vacuum cleaner like a Kirby that gives you the option of blowing air out the back or exhaust. I'd be concerned about using a blow dryer. I don't think blow dryers are made to be turned on for too long, and it seems like you could start a fire risk getting shocked.

paolobertoncin (author)2017-08-08

wow great job thank you

X-Ray2033 (author)2017-04-05

Still working on getting the things I need for this! The thing is I'm Australian and none of the hardware stores around me has plaster of Paris in larger quantities than 2kg... anyone got any suggestions on what I could do? Is there a substitute for plaster of Paris I can use that will weild the same results?

uwotm89 (author)X-Ray20332017-04-16

They have 2.5kg plaster of paris at Bunnings. It costs $8.09 which is better value than their 3kg one.

bigredlevy (author)uwotm892017-07-17

You need 2 bags. I used ~3.5 kg total for lid and body of furnace.

trainkid93 (author)2017-07-11

Hey guys, I've got a question for those who have built this. I know that in the pictures, TKofR used a 25 lb bag of plaster. If you start with a full bag, about how much is actually used including building the lid? I don't want to end up having a lot of plaster left over thats not going to used.

ThankGod SylvesterO (author)2017-05-30

Nice steps. But my question is can this furnace be used to melt gold and silver or can it produce that temperature of needed to melt gold or silver. Thanks for i await your candid responds..

skyholzinger (author)2017-05-19

I cast my foundry a week and ago and the insides still feel damp. Has anyone had this experience? I'm nervous to fire it up because the moisture may crack it.

TheMrCode (author)2017-05-06


L_inden (author)2017-03-21

Is play sand preferred or could I use regularly sand from say the beach?

PatrickE65 (author)L_inden2017-04-23

stay away from beach sand. Too many variables. Try to stick with non-silica playsand

Mazaya (author)2017-02-11

How much kg plaster of Paris do i need ?

Readitoveragain (author)Mazaya2017-03-20

900 around

JunoB2 (author)2017-02-07

I used the mixture suggested and i was very disappointed the next morning to find that i had been hit by a major major cold snap which caused the temperature in the house to be less than ideal in the house and my plaster took two extra days to set. on top of it now the plaster has a micro fracture in the plaster barrier. will this cause my forge to fail?

paolobertoncin (author)2017-01-31

Great work!!

Chandler slowik made it! (author)2016-11-25

I made it. You should use vaseline on the side ot the lid and bucket to make it come out a lot easier. Good luck

Just wondering how do you store it? I was advised it can't be stored outside in cold/wet weather? If so how do you get around this?

SeanF86 (author)2017-01-07

Followed the instructions to make the furnace and the lid - perfect - ours looks just like the video sans the paint job.

real challenge is the crucible - can't find any cheap fire
extinguishers (not dropping $20 for a new one) and it seems that no one
in my area has steel pipe in the 3" diameter range - it's all plastic in
this area.

Checked around eBay and it seems that the
A4 Salamander is the best bet - about the same dimensions as the home
made one and has an inside diameter big enough to fit a soda can.

is with the graphite crucibles is that apparently you have to preheat
them before use "avoiding local impingement of flame."

Any suggestions?

I've seen empty propane canisters used - you should be able to get one from basically anyone who going camping much. I found a video showing how to cut them safely:

DavidW21905 (author)SeanF862017-01-17

He wasn't saying you can only use a fire extinguisher, What you should search on amazon is a lead graphite crucible it is $30 but it will last 20 times as long as a fire extinguisher and a fire extinguisher wont be any cheaper. That is what the king of random uses and i use it too and it works great

ecogeeco made it! (author)2017-01-10

Awesome! I saw this when you first posted in 2015 and wanted to make one. It took around 3 hours to make it (all but the lid that we plan to make asap. I fired it up and made my first ingot tonight! Thank you for sharing! One thing to note for all the people that want to make one. Check to make sure that the extinguisher that you want to cut IS STEEL as the first one i used was aluminium and it melting really fast. live and learn I guess.

Davehacke (author)ecogeeco2017-01-16

I saw one on Pinterest where they made the crushable basically the same way as the furnace using 2 different drink cups as a mold

SamuelM164 (author)2016-10-16

I did everything in the video, I fired it up and it worked all right. But now the walls are cracked and prone to chipping off chunks if I look at them funny. How do I repair it?

benlathwell (author)SamuelM1642017-01-16

The king of random made a new video on it. If you haven't seen it yet, put grade #3 steel wool in the bucket while pouring the mix. It reinforces the walls and makes them less prone to cracking.

joshuamensch (author)2016-12-15

has any one tried wood pellets if so can you comment with your results

MattC43 (author)2016-05-21

After doing the charcoal version I quickly realized the need for the propane torch to heat this thing. Now my problem is that I get a hole in my crucible every time I fire it up. I've tried 1 extinguisher, 2 propane tanks and a stainless steel camping cup. Any ideas??

Chandler slowik (author)MattC432016-11-25

Invest into getting a real crusible on a site like Amazon. Good luck.

Kodsterrrrrrr890 (author)MattC432016-10-18

Get a graphite crucible, they are like immune to anything

MrS26 (author)MattC432016-06-01

If you dont mind spending a little extra money you can buy a graphite crucible online ive got one myself it works great

XFrodoBagginsX (author)MrS262016-09-14

ell i used a graphite crucible for a coal furnace and it got holes in it after the second burn, i guess the direct contact with the coal is oxidising the crucible very fast, i thought about a steelpipe around the crucible. any other advice ?

smay05 (author)MrS262016-06-26

If you don't mind me asking, where did you get your crucible from. I have been looking on ebay but don't know which one I can trust

lowdownkilla (author)smay052016-09-04

I went to a local plumbers shop and bought a 4 inch diameter pipe that is about 6 inches long and threaded on the both ends. Then I bought an end cap for it. It was kind of expensive, but I am doing a 6 gallon bucket and had the room to make it a little bigger.

MrS26 (author)smay052016-06-30

You can get one from amazon, heres a link

MrS26 (author)smay052016-06-30

You can get one from amazon, heres a link

CS23 (author)MattC432016-07-05

use a steel crucible or a carbon rod one.

Chuzzlepuff (author)2016-10-06

hello all! after skimming through the comments it has become quite apparent that spending the extra time and money to get better refractory materials will make a better crucible that this PoP design... however, with me being an amatuer science hobbyist and doing a wide variety of different and unrelated things, i will likely only use this crucible a handful of times... do ya think it's safe enough to just use the PoP design? its simple, quick to make...and i allready have all the materials on hand. the only changes i'm gonna make are to reinforce the plaster with some chicken wire and steel well as use my air compressor as the air source (you can conveniently adjust the output of the nozzle). for the liquid retaining cup i'm gonna use one of the tall blue propane tanks, and arc weld a pivot handle onto the cup half. is the alloy in arc welder electrodes comparable in melting point to steel? that is so the handle won't melt

lowdownkilla (author)2016-09-04

I got the 6 gallon bucket and 10 quart plastic bucket, 4inch pipe with cap etc.. everything from your video.

The only difference is I am using play sand and plaster of paris. I am not sure what the exact mix I need. With the 6 gallon bucket, the displacement of mix I need is about 15 quarts like you said in your video. So what is the mix I need. 1/2 sand, 1/2 plaster of paris, 1/4 water? Do I need to included the water in the three part mix to add up to the 15 qt displacement? Or do I just mix the dry materials to the 15 qt and then just add water on top of that? 7.5 quarts each of plaster of paris and play sand?

About This Instructable




Bio: Random Weekend Projects
More by The King of Random:5 Ways to Start a Fire, Using Water How to make a Batarang like "The Dark Knight"How to Make Ninja Stress Balls
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