Instructables

Build a furnace, create custom molds, cast a piece of jewelry, then mount a custom cut stone

In this instructable I show how I built a furnace - very similar to another design, just scaled down a bit. To view this project and some other pretty cool ones I haven't had time to transcribe over to instructables visit my site mechanicallyinclined.net

I designed a piece of jewelry, made a mold using the lost wax technique, cast the piece of jewelry then set a stone in it. All the materials are easily obtainable. It works with precious metals but if your on a budget and even cheap jewelry from Wal-mart can be melted down and used. It makes an attractive piece that carries a certain homemade charm (no pun intended) without the tacky homemade look. I made a necklace, but the technique can be applied to rings, bracelets, earrings, glasses, small machine parts... really the only limit is your imagination. (although for highly complex designs with many small or detailed surface features you may need to build a centrifuge which I describe near the end)
 
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Step 1: Gather Materials

A list of required materials

Furnace
-1 Quart paint can
-10 LB bag Quickrete
-Butane torch
-1" x 7" pipe
-1/2" diameter steel pipe
-3/4" diameter copper pipe caps
-10 Ga. Steel wire
-Brick (without holes)
-Something to mix the concrete in
-Something to mix the concrete with
-Small piece of cardboard
-Masking tape
-Hand tools
-Dremel (optional)

Molds
-Faster Plaster
-Water
-Source of wax (unscented candles work well)
-Carving tools (exacto knives work well)
-Small wooden blocks
-Heat source (microwave works well)

Casting supplies
Any metal with a melting point under ~2000 Degrees F
Small fire to heat mold, camp stoves work great
Pliers

Finishing Tools & Supplies
-Polishing compound
-Dremel with: Polishing Wheel, Engraving Bits (optional), Diamond Cutting Wheel (to cut stone)
-Fine sandpaper (if casting is rough)
-Claps, rings, fasteners, chains etc... (available at most craft stores such as Michaels or Hobby Lobby)
-Marine grade epoxy (to set stone)
-A box to put finished jewelry in (optional)

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sdfgeoff1 year ago
Just a note, you may want to change your site title from 'Untitled Document' to something a little better.
In the head tag of the page add:

<title>What you want the title to be</title>.

curvy771 year ago
is it possible to place the stone in the mold (loosly) than pore the metal on top, so that the metal forms around the stone? this will eliminate the need for the epoxy.
will it cast aluminum alloy such as t-6 for casting lower recievers for ar 15 assault rifle castings?
......dont understand much of what u said, but i beleive ur asking if it can melt
aluminum t-6 alloys? for some rifle castings? it depends on what was used to
generate this alloy. Hmmmm, this particular one is just aluminum that has

been heat treated and artificialy aged sooooooo, it shouldent be much of a
problem. however depending on size and quantity of what u want to cast u

may need a bigger forge fire. i myself use a fire pit with a metal bottom, started
with wood with coals later added and with a constant current of air generated

by a (small) carpenters blower. the carpenters blower has about 3-5 times
mor force than a hair drier and a wider front. this means more air and more heat.
Hi, Was wondering...what silver were you melting? I was hoping to use coin silver, which is 90% Silver, 10% copper. Would you be able to melt that in this forge? Also, if you could melt it, why wouldn't the crucible, being copper, melt?
melting point for silver is about 1790. which is plenty lower than 2000. so you should have no problem melting the silver part. however i recomend that u put this coin silver in an iron or steel caseing (held by pliers) with holes in it to drip into a crucible. this way u can get pure silver and be rid of the copper. (copper melting point is 1971 F)
curvy772 years ago
can soft clay be substituded for plaster or does it have to be baked clay?
0087adam2 years ago
Hmm i have some modifications to the original design that i will implement in my furnace. Isn't the lime in the concrete explosive at certain high temperatures? I'm also wondering what kind of metal your melting down and if this will go hot enough to melt steel or iron.
Avasar100003 years ago
Is this method sufficient for casting silver?
Would the crucible need to be a different material?
Melting pt. of silver is about 2000 F.if he were to use map gas which will hook to the tourch he has he may be able to melt it,I do know map gas gets a couple of hundred + degrees more than propane.Mapp gas comes in a yellow disposible tank and is available at any home impr.store.
spylock spylock3 years ago
M.P. for silver is 1760 F and using map gas in his setup he shouldnt have any problem melting it.Using a Turbo tourch head will give him an even higher temp though they cost about 3 times as much as the generic tourch head.
so just to get this correct....... the wire that you taped to your desk in the 5th picture is touching the wax carving so that when the plaster dries there will be a hole that the wax can drain out of. right?
And that you can pour metal into.
annaliesa!3 years ago
THe paint can /quickcrete furnace idea is pretty cool in theory- I'm concerned about the chemicals in the quickcrete- I checked out their msds - lots of hazards which could be exacerbated by heating the concrete up to metal melting temperatures. Furnaces are never made with commercial concrete, they are made with special bricks that are designed for high temperatures. The only reason I am concerned is that I've thought about making my own furnace but decided not to because of the hazards. Otherwise a great idea! I LOVE your mold/casting demo!
solarmew3 years ago
i just looked at the Quikrete website and there's like a million different quikretes X.X ... which one is the best to make furnace with?
In the FAQ it says that to repair a fireplace they have quikrete that can withstand up to 300 F, but isn't that kinda low for a furnace?
how would i make a 2 part mold like if i wanted to use my grenade and make a mold of it and fill it with aluminum how would i put those 2 molds together
This is just a basic brief on how to do it 1) get some playdough/ poly clay/ mouldable clay 2) mould clay onto one half of item and let dry/set 3) mould clay onto other half (making sure both sides don't join (talc powder works well) 4) when both sides are dry, remove item 5) hold together and make a hole to pour in liquid wax (hole can be made on previous steps 6) pour in wax 7) remove wax blank and tidy join 8) Add a wax sprue 9) suspend in plaster with sprue poking out of top 10) when plaster is set, put upside down in an oven so wax melts out 11) while mould is still hot, pour in metal
avatardub4 years ago
hey can i make ceramics instead of concrete part ? thanks !
EMC454 years ago
Have to agree with robotmastern. The buffing compound is probably a bit course for the jewelry. Red jeweler's rouge is where it's at. Than hit it with some white rouge and you're in business. AWESOME instructible all the same. I have had in interest in lost wax since the early 90s in high school. You have revitalized it!
 you could find a jewelers polish at your local hardware store and get the metal to be a nice mirror finish, don't use it on stones though it doesn't come off and just gets trapped in any grooves.
I think I'll be building one of these this weekend. The first practical item I wanted to make is an adapter from my CO2 tank to my welder. Without the centrifuge could I cast, say aluminum, and get the detail of the threads on the tank or will I have to make the hole smaller and thread it after casting? I'm trying to avoid spending $100 on the adapter if I can.
Better off casting slightly larger and then using a tap and die set (if you don't own one rent or borrow or just buy one) to cut the the threads.
swighton (author)  seabeepirate4 years ago
I think it is unlikely that you would be able to attain the detail of the threads without a centrifuge. If it was an extremely coarse thread you might possibly (I repeat POSSIBLY) be able to cast it with the "thread" part of the thread slightly wider than it needs to be, then file it to shape. The other worrisome thing would be surface finish of the seals. It might require a bit of finish machining on the o-ring seats to attain a good seal.
Asbestos4 years ago
Another question: (thanks for your previous answer!)

In your materials you list a 1"x7" pipe. I assume that this is the pipe that goes inside the quart can to make it hollow.

But my quart cans are only 5" deep. Are you using can with another dimension?

And a 1" diameter hole seems way too small. From your last picture on Step 2, if that small copper cap is 3/4" in diameter, I'd estimate that your inner hollow is at least 2" in diameter. Would you say that sounds right?

Thanks!

(I'm setting this all up in my workshop right now, and keep getting confused by the various dimensions listed)
Asbestos4 years ago
Question: Is curing the concrete in this way (drying for 2 hours, then the oven, then the blowtorch) better than 24-48 hours drying on its own? Is it just a matter of doing it faster, or is it actually better?

Also, I'm a little confused by the direction the bottom pipe is supposed to go in. In your pictures on step two, it looks like the pipe (and the blowtorch's flame) go straight towards the center of the furnace.
swighton (author)  Asbestos4 years ago
I don't know if allowing it to cure for 24-48 hours on its own gives better results. I would image it reduces your chances of the concrete cracking because of internal stresses from uneven cooling. If i was doing it again I would probably let it cure for two days. In this instance I was in a hurry.

The pipe is supposed to be approximately tangent to the wall of the inner part of the furnace. The idea is to cause the heat to convect around the crucible rather than heat up a spot on the side of the crucible thats touching the blowtorch. My implementation of it sort of failed (e.g. I didn't get the pipe orented properly) and as a result I burned a hole through several crucibles because of the intense heating in one spot. Basically follow what I wrote and tried to explain, not what my picture showed ;)
heavyhadron4 years ago
There are other alternatives to purchasing or making a centrifuge that I have used with varying success to get fairly fine detail in my castings.  The usual disclaimer applies here - there are many ways to hurt yourself doing this.  Use caution, follow shop safety rules, and stay aware of what's going on and you can minimize the dangers present.  I am in no way responsible if you hurt yourself doing this.

     One alternative is to steam cast.  Instead of putting your wax into a foam cup, put it into some sort of metal can (soup can with top and bottom removed works) - this is called the casting flask.  Also, make tubes of wax and weld them onto the back of your wax piece (they are called sprues) at multiple points to allow the metal to flow evenly.  The farther the metal has to go, the less detail you can put into the piece.  Also, at the other end of your sprues, you want to make a small bowl shaped area to hold the metal as it melts (this will act as your crucible now).  But more importantly, this depression (called a "button") holds in extra heat so the metal will stay liquid longer as it flows through the mold.  Pour your plaster around your piece and cure it.  Burn out the wax (heat it in your furnace until about 500 degrees, or until all smoke has stopped coming out.  Place the metal to be cast into the button now and put it back into the furnace.  Let it all get nice and hot, melting the metal in the button, or getting it close.  Then pull the whole thing out and place it on either a firebrick or on some concrete.  Heat the metal up more using a torch - you want it nice and liquid, and you will see patterns swirling around - that means it's hot enough now.
     Now comes the fun part.  Wear some type of gloves while doing this - I use gardening gloves that are soaking wet, stuffed with wet paper towel in the palm - this give me good control and still gives some protection.  While you were waiting for the metal to melt, you have prepared a lid from a pickle jar, or spaghetti sauce jar (metal, threaded lid) by placing a couple of folded paper towels into it and getting it wet.  Take this wet jar lid/paper towel combo and place it on top of your casting flask and melted metal (which is still liquid).  Press down HARD - use your body weight!  You will hear the steam hiss, and hold it down for 30 seconds to 1 minute.  Congrats!  Your piece has now been steam casted!  I like to throw the whole thing into a bucket of water and the plaster just crumbles out, but remove from the plaster and finish as you see fit. 
     A note - it helps to have more metal in your button for steam casting than other methods - the button is a heat battery, basically and the steam will consume part of that.  So to compensate, melt more metal when you cast this way. 

I hope that helps you in you casting fun!  It is certainly the most fun way to cast for me.
mr.space5 years ago
i take it you could use plaster of paris instead of faster plaster?
swighton (author)  mr.space4 years ago
Yes - faster plaster is just a microwavable version of plaster of paris, it allows you to cure the molds quickly in the microwave instead of waiting a day
spylock4 years ago
Lead is deadly,and shouldnt be used for anything,craft or household wise,we dont even use it in plumbing anymore because of the toxic effect and it dosnt take much.
thoraxe5 years ago
hmmm....this could have been better. what you should have did was carve a "sprue" into your wax model, which is basically a small cone whose point touches the model. then you would make the mold around the entire model, leaving the widest part of the cone uncovered. this forms a nice opening for metal to flow into. basically this allows much more intricate shapes to be made without having to have that open casting.
swighton (author)  thoraxe4 years ago
I agree! Though the only way to attain more detail via a sprue is to use it in conjunction with a centrifuge - I made a centrifuge from a bicycle very checaply, I detailed the process for a ring I made using centrifuge casting on my website. You can check out the link here.

http://mechanicallyinclined.net/page_the_ring.html
tjk94 thoraxe5 years ago
Actually if using a clothes hanger to hold the wax well the plaster is drying it wouldn't be that hard to do. Just mold it as usual but completely cover the wax with plaster, melt the wax out then widen the hole from the clothes hanger.
nodrog195 years ago
What did you use for a crucible?
BTW, using plaster instead of cement to insulate the furnace does not work.
sosimonita5 years ago
This post saved me money on classes...thank you
dciocoiu5 years ago
what is Quart paint and can i find it at home depot?
dciocoiu all it is is an empty paint can that held 1 quart of paint in it
chemisti35 years ago
where did you get the epoxy.. i cannot find specifically the clear drying marine grade epoxy... the marine grade epoxy ive seen are white drying... can you give some specs of the glue you used?
dciocoiu5 years ago
What is Quart paint and can i faind it at home depot?
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