# Plans for building a home made furnace



## lazersteve

All,

I'm looking for the best plans for a homemade *electric* furnace. I want to make a video of this project and also need a furnace for my shop. I have one set of plans and most of the materials to complete it. I want to get your feedback before I start. Maybe someone has a better set of plans than I found on the internet. To keep costs down the plans will have to be free. The furnace will be for melting gold and silver.

Thanks in advance,

Steve


----------



## goldsilverpro

Do you want a box furnace or a pot (crucible) furnace? IMHO, the only thing a box furnace is good for is fire assaying. To me, when melting gold or silver, you need to be able to chemically flux the metal, in order to improve the purity. This is very inconvenient (if not impossible) to do in a box furnace. It is very easy to do this in a pot furnace. Also, in a pot furnace, improving purity is probably 10 times more efficient than it is in a torch melt. With a pot furnace, you can also see what's happening.

If you do want a pot furnace (which I think is what you need), why, oh why would you want to go electric? Building a small gas pot furnace is much more simple (and cheaper) to build than an electric furnace. You also don't have corrodeable elements or expensive controllers to worry about. You can use natural gas, propane, etc.


----------



## lazersteve

I'm definitely after the pot furnace. I want to design it around a small crucible that I have. Gas is not not a problem, the only reason I said electric is that is what the plans I have called for. It would be great to have a propane powered pot furnace to melt small amounts of gold and silver. Can I use standard grill burner parts or will I need special high temperature parts? What is the maximum temperature I can expect from a gas powered furnace?

Steve


----------



## jimdoc

Steve,
Have you checked ot backyardmetalcasting.com?

http://www.backyardmetalcasting.com/

http://www.backyardmetalcasting.com/gallery.html

You should be able to get alot of ideas from
some of their setups.
I like this one, as I have 2 boxes of firebricks, and 
the rest looks easy;
http://www.backyardmetalcasting.com/guest_martin.html

Jim


----------



## Anonymous

Hi

I have been collecting plans for different types of furnace / forge types lately.

The one is a coffee type forge says it gets up to 2,000 degrees. (gas)

Also information on the blowers, all home made.

If interested let me know.

I got them scattered around my hard drive as I haven't organized them yet!


----------



## lazersteve

Jim,

I'm going to use castable refractory cement to make mine. I want it as small as possible. I'm building it around a small 50 oz crucible. I would like it to be able to tilt for easy casting.


Steve


----------



## jimdoc

Steve,
Have you seen the one that action mining sells?
It looks like it is made from a small freon type
bottle. Jim


----------



## lazersteve

Dgoldboy,

I'm game! Please send them to me via PM when you locate them. 

Thanks and welcome to the forum,

Steve


----------



## goldsilverpro

Jimdoc,

I like the furnace on your last link. The burner set up is very simple and is very similar to what I used, when I used propane. You just put a piece of burning paper in the chamber and turn on the gas. After a few minutes, you slowly open the air. After a few more minutes, you close the lid and adjust the air and gas until you get about a 2" plume (tail) of flame coming out the exhaust hole in the lid. I used an old upright vacuum cleaner for an air supply.

I hate the way the lid works. I could see myself getting burned. How would you lift the lid without having your arm over the 2200 deg F. chamber? I much prefer a lid that pivots to the side. This can be simply made by welding two short lengths of pipe, one to the lid and the other to the top of the body. A smaller diameter pipe is inserted into these and acts as a pivot pin. Very simple and works as well or better than those common, complicated, lever arm lid raisers that you see on a lot of furnaces.

I would probably use a large diameter piece of pipe (scrap yard) for the body and the lid. I would weld a plate to the bottom. I would use refractory cement instead of bricks. I would weld 4 crossed pieces of rebar inside of the lid ring to hold the cement. To determine the inside diameter of the pipe that is needed, add about 10" to the widest diameter of the largest crucible you will be using. This will give a 3" refractory thickness and a 2" spacing all around between crucible and refractory. The pipe ring is also 3" thick. Some sort of mold must be used to cast the refractory in the chamber. The best is round thick walled tubing made of cardboard. I think they use it for molding round sections of concrete bridges. That way, you can cut the cardboard to remove it. Don't use a metal mold or, you never get it out. When casting the lid, use a tin can to mold the exhaust hole in the center. I prefer at least a 3" lid hole.

Somewhere, in one of my early posts, I went into this in more detail. It is, by far, the simplest furnace to make, maintain, and use that I have seen.


----------



## jimdoc

GSP,
I have the kit that Lionel sells on the backyardmetalcasting site, I just need the refractory. I also would like a smaller one like Steve is looking to make. I have a bunch of empty 134 freon bottles that I plan on trying.
But since I already have 100 firebricks, I am definately going to try to
build that one. You are right about the lid should swivel though. That site is interesting to see how other people have built their equipment on the cheap. You just have to redesign a little to your own liking or needs.
Jim


----------



## goldsilverpro

Are the bricks the light weight, soft, insulating type or the heavy, hard, refractory type? If they are the soft type, you can't use a flame directly on them. You can line them with about 1", or so, of refractory cement.

I always liked to have 2 furnaces. A small one, about a #4 or #6, for only pure metals and a larger one, about a #16, for whatever. A #16 is about the largest that one man can safely handle with only a standard pair of crucible tongs, without breaking the side out of the crucible.


----------



## jimdoc

They are the soft refractory ones.
I can also get the ones that they build
fireplaces with, they are harder, but
I was under the impression that the softer
ones are better for high temps. You are 
talking about handling direct flame though, 
so would the fireplace bricks work? They are
only 75 cents each, the soft ones are a few
bucks each, usually $5-$7, but I got the boxes
cheaper. I probably have enough of each to
build a furnace like the one we are talking of.
I was also under the impression that the harder
ones may pop or explode from the moisture at
very high temps. Jim


----------



## goldsilverpro

I just found about 6 commercial crucible furnaces, for copper, gold, and silver, on the net. All of them used a hard firebrick lining with a 2" insulating (probably soft firebrick) layer underneath it.

Every furnace I made was out of mixed refractory cement. I have never used firebrick. A number of pros have told me never to line a furnace with soft insulating firebrick. They said it wouldn't stand up to the direct flame and, I definitely know that it won't stand up to the fluxing chemicals or molten metals.

On this forum, there are two threads that prove this. In one case, someone was melting and fluxing metal, in an electric box furnace, that somehow escaped into the soft firebrick lining. Everywhere it landed, the flux and metal ate big holes in the soft firebrick. The guy posted photos of it. In another thread, someone was trying to flux melt metal, with a torch, in a dished out area on a soft firebrick. The flux and metal melted down through the firebrick and he had to dig it out.

No matter how good you are, you will always get flux spills in the furnace. Crucibles will wear thin and get holes in them. Melts will foam over, especially when using stuff like standard hydrated borax. Most all furnaces have clean out holes at the bottom for this purpose. 

Soft firebrick is called insulating brick and that's what it is used for - not lining high temp corrosive melting furnaces.


----------



## aflacglobal

AFLAC !!!
:arrow: :arrow: :arrow: :arrow: :arrow: :arrow: :arrow: :arrow:


----------



## aflacglobal

For the ones who might want to make the refractory from the one in the doc. Most of those items are easy to find. Don't let them names fool you. lol


----------



## lazersteve

Great info everyone!

As a side note I want to point out to everyone that refractory dust is not good for you. Be sure to read the MSDS on the refractory material you are working with. Typically a good filter mask is a minimum requirement.

Steve


----------



## Ky.Sam

http://pacificcoast.net/~kerslake/BronzeSite/Studio/MetalCastingFurnace.html Sorry didnt check the original link posting the first time.


----------



## aflacglobal

This is something like i was talking about but smaller and you drop it in from the top. No lid removal. Note the static air pressure i was talking about. The flames just naturally push their way out with ease. Notice the rushing sound, but little push.

:arrow: http://www.youtube.com/watch?v=QNm4Kb0wCsw


----------



## Noxx

Steve, where did you get your refractory cement ? Do you have enough sell me a few pounds ?

Thanks


----------



## Noxx

The «coffee can furnace» is suited for my needs.
http://www.backyardmetalcasting.com/ccfurnace01.html

But buying 50 pounds bags of the required cement is mostly useless.


----------



## lazersteve

Noxx,

PM me and we'll talk about it.

Steve


----------



## Cobraj

Hi all,

One thing I know is Propane, and that is because I work building, repairing and refilling propane tanks and appliances for a propane company. What the pictures are showing is ok but it could have much more info. Like, that should be a high pressure setup. This isn't something you can hook a gas grill line with regulator too a think it will work correctly. I don’t believe this type of furnace needs air supplied force added to the mix. From the pictures it is defeating the purpose of the firebox being in a cylinder shape. Forcing air in is heating the one side of the furnace cherry red while the rest stays much cooler. The idea would be to have the flame swirling around the crucible from top to bottom not heating the crap out of one point that is opposite the burner’s intake. This setup is and has been used many years in things like tar buggies and furnaces like this. I have never seen one that had any other gas or air hooked up to it then Natural Gas or Propane. The trick is to have a starting base for an orifice size, then have an air shutter that will be set and forget it. You need a high pressure regulator not a 12 ounce regulator like on gas appliances. Then you need to figure out what BTU you need, match that with a mixing (burner) tube diameter, then match that with a orifice size and have an air shutter that will handle the highest pressure the regulator can output. Once your setup at the highest pressure the air shutter doesn't need to be moved. If you buy a adjustable high pressure regulator you can adjust the amount of heat as you need it from the highest heat to a keeping the box warm to fire up again low setting. 

If this doesn't make sense please correct me. It is much easier to make then you think. I believe so companies still make everything from the hose to the orifice in a high pressure burner kit. I would have to check it out too; I was planning on making one myself in a month or two. :wink:


----------



## jimdoc

Here is a link on where to get the high pressure
regulator;
http://www.cajunshoppe.com/regulator.htm

It is from a page on backyardmetalcasting;
http://www.backyardmetalcasting.com/propanerig.html

I still need to get one of these also as well as the refractory.
Jim


----------



## Cobraj

Hi Jim,

He has it all on the site GREAT! I think I'll build this one it looks like to strong of a flame but the design info looks good. Thank you! BTW no air line is added in this design I thought someone said that.


----------



## jimdoc

Cobraj,
I think that site is awesome, I have his furnace kit,
but need to finish it. I see he has added some pages 
recently on melting iron;
http://www.backyardmetalcasting.com/harriette01.html
Jim


----------



## Cobraj

HI,

You could use 3/8 copper tubing that is flared 3/8 nuts and buy an adjustable high pressure like on the link, order a 100lb propane cylinder from your local propane dealer (that20lber won't last long and may freeze up). 1/4 to 1/8 adapter, plus the tubing in the specs and your set.


----------



## EVO-AU

Have you trried LINDSAYBOOKS.COM ? They have books on just about everything in the metals hobby runs, plus some designs for building furnaces. Some are electric and some are gas. Very explicit and exremely easy to build. I've built two over many years and not been disappointed. 

EVO-AU


----------



## goldsilverpro

My main complaint about propane is that the tanks freeze up and will eventually shut down. Even a 100# tank can shut down in a couple of hours, in a cold climate, if you are running a large enough furnace. You can tell how much propane is left by observing where the freeze line is.


----------



## Cobraj

Hi,

That is correct. If you use it alot you could get a 420 which is 100 gallon or use [email protected] 100lb tanks. The more area that is exposed to vapor the less of a chance of freezing up. Or you can use a blanket to warm it


----------



## Noxx

Does anyone tried to build one of the furnaces on
http://www.backyardmetalcasting.com ??

I would like to but I'm still looking for refractory cement lol...


----------



## Noxx

Do you guys think that it's possible to melt gold with an electric heating element of 1600 watts with 2300 °F Max element wire operating temperature ?
Thanks


----------



## catfish

Hi Noxx:

I melt all my gold with an electric furnace, 1500 watts, 117 volts AC, and at 2000 degrees. My little furnace will go to 2300 degrees F. in about 20 minutes. 

The only thing is that if you melt large quanities then it takes a little longer. I normally melt the gold for a bout 30 minutes in order to be able to pour it in to a mold. Just be sure the mold is hot. 

Don't make the same mistake I did. I placed my graphite mold in the oven at about 1200 defgrees F. and the damn thing caught on fire. I now heat my mold with a heavy duty heat gun for a few minutes before pouring. It works great.

Before I got my electric oven I used a mapp gas and oxygen torch and now after using this oven for the last couple of years, I would never go back to the torch. Too much sugar for a dime. Also you can keep reusing your melting dishes over and over. Cuts down the cost of doing business. It also requires very little flux to melt the gold. Not to mention the safety factor of an open flame and hot moltened metals, plus the gases they produce.

How is school going?

Hang in there, and please keep my good friend, Alfac straight, if that is even possible, ha-ha.

Catfish


----------



## Noxx

Thanks for the reply catfish.
Is it your home made furnace or you bought it ? Because I'm looking for plans for a small one. Everything I saw on the net is for melting Aluminum or Bronze... I will use a 1600 watt element (115V) rated 2550 degrees F.
Should be enough to melt gold. I don't plan to melt larger quantities of gold at the moment...
Thanks for the input about the graphite mold. I do own one too 

BTW, school is going great. And I do my best to keep Aflac on the straight way ! :lol:


----------



## EVO-AU

Noxx: Havee you tried Lindsay Publishing.com ...They have plans for electric as well as gas. I have built two of their furnaces over the years. You can see them on their website. Lots of other great stuff too. Stuff on metalworking from the 1800's, Fanrastic catalogue. Want to build a potatoe cannon? ? ?

EVO :lol: :lol: :lol:


----------



## Noxx

Thanks EVO but their website isn't working... I think the good website is http://www.lindsaybks.com


----------



## EVO-AU

Thanks Noxx, I get their catalogues regularly and wasn't aware of the website logistic. Appreciate the thought. EVO


----------



## Lou

I have a good connection on high quality refractory for cheap. If you're making an electric furnace, you would very much want to have a good hot face, but very little of it, but a lot of insulating material. Kaowool or a lightweight kiln brick are the best ways to go. If you go with kiln brick, you can avoid a hotface (unless you want to melt platinum and palladium, both those both require molybdenum disilicide heating elements, which are costly, but will give you 1800C). For gold, silver, and copper inquartation, I suggest Kanthal nichrome heating elements which are good to about 1200C. Buy directly from them, or off ebay, they're the same if they're new. 

I've built a few furnaces, some propane or waste-oil fired (these are for casting mainly), and others that are resistance heated (tube furnaces, and box furnace by Thermolyne). You'll find that building your own is easy, and CHEAP when compared to buying new or even used furnaces.

I've never built a resistance furnace before, but I've rebuilt/retrofitted older ones. All you need to build your own are the heating elements (1500W would be more than sufficient for what you're doing), a way to thermostat it (so a thermocouple of some sort, preferably a type S as they last the longest), refractory brick, a variac for controlling power delivery, and general electronics knowledge. 

I post at www.backyardmetalcasting.com forums under the same username, and indeed, there are many good ideas to be had. If you'd like, I can ask some other members there who have built their own versions of the ''Lil' Bertha'' or Gingery based electric furnaces.


----------



## Irons

I built one a number of years ago using a large coffee can for the outside. I wrapped masking tape around the nicrome coils and wrapped that around a cardboard form the dimensions of the inside. There were 3 elements which gave me 3 seperately controllsble heat zones. Once the elements were wired in and the core inserted in the can, I poured refractory cement to fill the space between the core and the can.

Once the cement was dry, I baked it to drive out any moisture and when I powered up the elements, the cardboard core and masking tape burned away and voila, the $20. furnace.

I used it for pulling crystals from a melt and presented a paper at an student ACS meeting. I have a nice certificate on my wall from the American Chemical Society for that project.


----------



## Lou

Neat Irons!

There are some very cool things you can do with crystal pulling. Aside from zone refining, it's a damn good way to get extremely pure material (single crystals). There are even ways to make a whole crystal orient a certain way.


----------



## Irons

It was really rube goldberg apparatus.

I mounted a spindle on an old electric clock mechanism and a bit of string with some Pt wire to hold the seed crystal.

It had to be cheap because none of the faculty would sponsor me because they thought I was nuts, so I had to do it out of pocket.

When it came time to present my paper, they all volunteered to be my sponsor.

I was the only student that didn't have one that year.

I went back to visit 10 years later and they still had the apparatus and crystals on display in the main hall of the Physical Sciences building.


----------



## Noxx

Hello,
I just called some places and I could buy 5L of refractory mix for 30$ (up to 1600°C). Is this a good deal ? And can it be used as a good hot face ?
I already have regular firebricks but I haven't find the lightweight type yet...


----------



## Lou

Regular fire bricks will take a hell of a lot of abuse.

1600C is pretty good, and the price is ok, but it's measured in liters, which would make me think that it is a rammable material rather than dry mix. Sounds like a great deal then, that's probably 50+ pounds and not bad for where you live.


----------



## Noxx

It's not dry mix...

Firebricks will take lot of abuse but do they'll absorb a lot of energy as well ? Does a kiln made with firebricks and refractory mix has a good efficiency ?

Thanks


----------



## Lou

No. You want kiln brick for insulation, they insulate very well and you can cut them with a cheap bread knife. You'll have a tough time cutting a fire brick with most anything.Obviously they are fragile, that is when a hot face refractory comes into play, it takes all the abuse from tongs, crucibles, slag, etc that would ruin your kiln brick. Fire brick is just vitrified fireclay, and in my opinion, is useless outside of the industrial setting, unless you're lining ladles or cupolas for iron melting...


----------



## dixie

A couple of years ago the welders in my area switched over to PROPANE because it was a little cheaper than ACETYLENE. Now they have all switched back because it will not produce the same heat and does not burn as clean.

Why could one not use an old torch set-up with a rosebud tip to heat their furance.

MIke


----------



## Lou

Oxypropane isn't as hot as oxyacetlyene, not by 1000 degrees. It's much cheaper, and much higher pressures can be used (no 15 psi limit), but yep, doesn't get as hot.

But why can't you use an old rosebud? Well, I would think it's because they're not designed to run inside of a furnace, and that they run way too rich without having additional oxygen to lean out the flame. More importantly for me, the oxygen required is really expensive, why not use compressed air and adjust the ratio, or better yet, just use a Reil burner which works and works well.


----------



## zauggart

im new to here and read the post upwards about useing a casting home made furnace . wouldent the air pressure from the fan blow the gold particles and leaf all over the place? 
ian


----------



## Lou

Just use a piece of graphite as a cover to your crucible. I do that for silver powder melts. Also helps to wrap up your powder in coffee filters.


----------



## gotgoldfever

This site has some really cool propane burners for sale. Perfect for a home made furnace.

http://www.hybridburners.com/index.html


----------



## ashir

i want prepare a home made tilting furnance. i wast use waste oil as fuel, have any one idea that i can follow?


----------

