myfordboy's furnace

After making quite a few castings using just a large propane torch and a pile of fire bricks I thought it was time to make a proper furnace. The torch and fire bricks works ok, but is a pain to set up and wastes a lot of expensive gas.
I looked around for a suitable sized steel dustbin ( trash can)  but couldn't find one suitable at the time, so decided to roll my own.

This is how my furnace was made.

I bought a small sheet of 0.5mm steel from the local DIY store and some 25mm x 25mm steel box section. The sheet steel was cut to size and rolled to form the body and the box section added to form the legs. One of the legs is longer than the others and extends to the top of the furnace.
50mm x  6mm galv screws and nuts were used to join the ends of the sheet together, passing the screws through the long leg and into the steel casing. There were left full length on the inside as this will help hold the refactory in place.
 A hole was made for the tuyere and a disc of MDF cut to be a snug fit on the inside of the casing. Two further pieces of MDF were cut and holes made in them to suit the outside diameter of the casing. These 2 formers were placed as shown below to keep the casing in shape when the refactory is added. The disc has a sheet of plastic laid on top to prevent the refactory sticking to it.  

The disc in the photo is resting on top of some wooden packing equal to the height of the plastic paint can which will be used for the inside former, less the thickness of the disc. The 20mm dia white plastic tube you can see was to form a trough and escape hole for any metal spills but this has proved to be too small. 

Update 22/07/14
If I were to make another furnace I would not bother with the drain hole but add another inlet in the side for a blower. See the details of my blower at the bottom of the page. This has speeded up melt time as well as using less gas.
The Refactory.
From a garden center I bought a 100Lt bag of  Perlite and from a stove center, two 12.5 Kg tubs of Fire Cement. After the job was finished I had half a bag of the perlite and about 1/4 tub of fire cement left.
The mix is 4 parts of Perlte to 1 part Fire Cement by volume. It is not that easy to mix so and I found the best way was to add a little water to the fire cement and mix in a bucket using your hands ( wear rubber gloves). Any water added has to be evaporated before the furnace can be used so as little as possible was used but enough to make the mix workable.

At the bottom, some galvanised steel wire was tied between the protruding screws inside the casing to help key the refactory to the furnace, like the reinforcing bars that are used that in concrete.

The mix was then added .........

.....and smoothed to a nice finish.

This now has to be left to dry. It could take a few days depending on the air temperature in your part of the world. When it was dry enough to handle it was turned over and the disc removed.

For the inside former I used 5Lt + 10% extra free, plastic paint can. A further piece of the metal sheet was bent and added to the outside to make a bracket which will later hold the burner. A tube of silicone was used as the former for the tuyere. The screws were again left long on the inside of the casing.

Another mix of refactory was then added around the former .This was then left to dry naturally for a few days until I felt the former could be removed. Once it was removed a 60 watt light bulb was suspended inside to speed up the drying process. Next I dried it further by putting it inside the kitchen oven. It just fitted. Since the furnace was made we have had a new oven and I don't think my wife would let me do this with the new one!
You can see in the photo below I also added a ring and rods to give extra support to the bottom.

The lid was made in the same way as described to the dimensions shown in the drawing.

The Burner
I already had a Sievert propane torch set which has an economy setting, the main flame can be shut off and a smaller flame kept going. I made a new necktube to fit it using a jet from one of the nozzles I had. It is not essential  to use a torch handle, a simple gas tap would do the job. I use an adjustable regulator set at 2 Bar (28psi) and this incorporates a hose protection valve which cuts off the gas if the hose should fail.

 A hose clip determines the length of tube that goes inside the furnace.

                                         Close up of the jet.

To hold the burner in place the bracket shown below was added, the holes are a loose fit on the burner tube. The burner tube is not sealed into the large hole in the furnace (this is called the Tuyere) This allows air to be admitted around the burner.

The furnace was heated up slowly several times to prevent cracks before being put into service.

The Kasenit Furnace
If you are following my metalcasting videos you may have spotted I am using a different furnace in  Part 29
This is a commercial furnace that was recently given to me. It was in a rusty condition but a clean up an a coat of heatproof black paint smartened it up. It was originally made for town gas but the previous owner had changed the jet and it now runs on propane. 
By coincidence the internal dimensions are identical to my home made one.
I was interested to see how it's performed compared. 
The main difference in the design is the vertical air inlet to the right of the burner, and the design of the burner itself which screws into the side. There is no hole in the bottom.


Well I have to report there is no noticeable difference in performance. I have not measured the gas consumption of the home built furnace but I have recorded it for this one.
I was surprised how little I used. I weighed the gas bottle before and after the melt and found 0.3 Kg had been used. From this I got 3.88 Kg of metal after the dross had been removed.  

The advantage of the Kasenit furnace is that the refectory will be good for melting brass and bronze if I ever need to. The homemade one with the perlite lining is not designed for the increased temperature though ideal for aluminium melting.

Update 16/07/14

For a year or so I have been using a clay/graphite crucible in place of the home made stainless steel ones. The reason for the change is the stainless steel storage containers don't seem so easy to get now and they are thinner. This meant I could only get about 3 melts from one before it sprung a leak.
As expected the time taken to melt the metal is now longer. With a stainless crucible the heat from the burner is transfered  easily through the metal but with the graphite one the whole furnace needs to brought up to temperature.
I have been using the burner supplied with the Kasenit furnace without any thought but one day I had my hot air gun handy during a melt and blew some air into the vertical slot next to the burner. It seemed to make the burn more fierce but it did not reduce the melt time.
Then I thought I would try my home made burner with the blower and it was a big improvement. 

The blower was taken from a hot air gun

How the blower was made

Temporary set up to evaluate blower

Finished burner with blower

Flame pattern with new burner

 This is the Amal burner on the same pressure setting, 2 Bar

New burner design.
I have simplified the burner design to use plumbing fittings and no jet is now needed. Easily made in a hour or less. 

The video above shows the construction.
Here are the dimensions:
15mm copper tube 80mm long
20mm steel conduit 225mm long
Hole for the gas jet is 1mm dia.
I tried the burner with  the 20mm steel tube and also a 22mm stainless tube.
Both worked equally well, I used the 22mm one in the end as it fits the hole already in the furnace.

Check out my other pages on furnace and burner building


  1. Hey There,
    I don't know what kind of stainless steel pots
    you've got over there, but I've tried everything
    between 1/4" walled SS pipe to malt mixing cups
    and melting scrap and alum. cans has ate out the
    wall on every one of them in the first two burns.

  2. Hey Grandpa Bill, that sort of thing happens when you're got too much air entering your furnace. Ideally you just want only as much air as is necessary to support combustion, any extra just cools down the furnace and oxidizes whatever's inside. So, cover your drain hole and plug up any extra space around the outside of your burner tube and your crucibles will probably last a lot longer.

  3. Is there a reason that the hole on the lid is offset? How many melts do you get out of that propane tank?

    I love the videos and watched most of the metal casting ones yesterday. This is an area that I hope to get in to very soon.

  4. MyfordBoy, I am also interested in what you are using for a crucible. I see in one of your YouTube videos you say it's a "steel kitchen container". I am presuming you mean the ones that come as a 4 or 5 part multi-size set with lids, for putting things like flour and sugar in? Is it stainless steel? I am also presuming you use stainless hardware, and the two "tabs" look to be flat iron bar. Thanks for all the information you've posted, and the thoroughness of your videos is appreciated.

  5. @Grg I can position the lid so the hole is in different places to get the best burn.

    @Ian The crucibles are like you suggest. Two metal plates are added for handling.

  6. sorry I do not understand a thing but the white tube and passing just to the lower floor?

  7. The tube was to form a channel and hole in the bottom of the furnace to allow and spilt metal to escape. The hole proved too small but a suitable size is shown on the plan.

  8. cement for fire must be at least 8 hours or quick drying?

    1. It takes much longer to dry out. Depending on where you live. I left it for a few days before adding the light bulb and oven treatment. Slowly is the way to go.

    2. Hello. After you made the Foundry and the burner tube i noticed on the outside of the furnice you added a piece of bent metal (picture 6 of 15) where you put the caulk tube in. What i am asking is how did you get the burner tube that is 3/4 inch OD to fit Snugly in the larger tuyere hole which is 2.00 inches in diameter. I also noticed on the completed Furnace refering to picture 13 of 15 you have the Burner tube inserted and it looks to me you added something to make the 3/4 burner pipe fit snuggly. Can you please Help!

  9. there was a question above about how many "melts" you can get out of a standard propane bottle, im curious too!

  10. I did wiegh the gas bottle once and compared it with the quatity of metal melted but I can't remember the results exactly, I think it was 5Kg metal for 1Kg gas. Next time I fire up I'll record the result.

    1. sweet thank you, iv been looking at this for weeks now and i want to get into it. here was my first attempt when i got too bored the day i decided to try casting, feel free to point and laugh :)
      i had an old coffee can with empty soda cans in it over w wood fire (pine, birch, pecan, sweet gum) the cans would get soft but not melt, so to make them melt i used spray paint (about 2/3 the bottle) to heat it up more. my make shift crucible supported by hand ( 3 pairs of gloves soaked in water) poured out 2 0z ish of liquid metal into a shot glass. after a few days my fingers were well enough to play on my computer i find your videos and this blog (should have done that first) now armed with information iv played with it some more (metal tongs after that first time) and more and more. its destructive creation and i cant get enough of it!

    2. I did a lot of casting before I built my furnace using a large (85kw output) propane torch and stainless stew pot. It is quite possible to melt the just same as with a proper furnace but the gas consumption is extreenly high and its not as safe or convenient to use. You could try a charcoal furnace with a simple blower. There are designs on the web for these. Please work safely, no more burn fingers.

  11. Thank you for your contribution...I want to use your plans to build this. Very well explained, but what do you mean when you use the word "former"? Are you using it to differentiate between two points, former and latter, or are you using it as a verb, as in to form something?

    And are you using two "formers" the outside being the sheet metal casing, and the inside being the paint can? And the two formers are basically used to shape the refactory (fire cement and perlite)?

    I just want to clarify because I am pretty new to this whole thing. I saw a foundry online for sale, the guy wanted like six hundred for it and that is crazy! So I want to build my own instead.

  12. From the Oxford dictionary of English
    "A person or thing that forms something: a tool, mould or other device used to form articles or shape materials."
    The paint can is the former, used to shape the refactory. The outside sheet metal is the outside former but is left in place.

  13. your videos are quite explaining the procces but can stailess steel bucket hold molten iron and

    1. No, it's only suitable for aluminium. You would need a regular foundry crucible.

  14. Two questions (and thanks for this information):

    1. I looked at the gas jet drawings and googled "Sievert propane torch" and it appears to be a "repurposed" blow torch with just the stainless steel pipe added. First, is this an accurate interpretation, and if so, what is the purpose of adding the long pipe? Why would you not put the business end of the torch as as close to the interior of the furnace as possible?

    2. Do you think using an aquarium pump or blow dryer or some such (low pressure) forced air source would increase the heat output or is the design of the torch such that it sucks in all the air it can use anyway?

    I have been playing with smelting lead using an outdoor cooking grill and a MAP gas torch, and am really interested now in building this and expanding my "foundry capabilities". Thanks for the information! It is greatly appreciated!

    And TIA for the two questions (actually, I guess at least three questions:)...


  15. After watching the video, I see you *replaced* the burner on the torch, so question #1 becomes "Why?". Why not just use the burner that came on the torch and make the furnace bracket so that it could hold it in place?

    Thanks again!


    1. Hi Allen
      You need to get the tip of the burner into the furnace. If you just used the supplied burner it would be too far inside and would not be able to take in the air. I only used the torch becace i have it. A simple gas tap would serve but the torch has an economy setting, there are 2 control knobs, so i can turn of the full gas supply when adding more metal and still keep a small flame going.
      Some burner designs use forced air as you suggest but its not necessay for melting aluminium. My design is economical with the gas.

  16. For drying out in the oven.. It's best to ask for forgiveness than permission...


  17. myfordboy,
    Over here we use the "Webster's Dictionary" and very rarely at that. I was wondering if you could omit the oven process. My wife would kill me if I tried that. Also, what is the purpose of the burner hole being offset?
    One last thing,could you elaborate on the pre-heat cycles you used to cure your furnace, duration, temp, cycles.

    1. The burner hole is offset and tangent to the furnace so that the flame swirls around the crucible.
      The refactory is dried slowly to prevent cracking, I can't recall the exact times but a 100w lamp was hung inside for a couple of days initially. If your wife doesn't understand you (!) and won't allow use of the oven you would have to apply heat slowly and gradually build up to a full heat.

    2. Hi myfordboy,

      first of all thanks for sharing your knowledge and experiences!
      I felt inspired to give this adventure a try too and am currently
      at the shopping stage.
      I plan on using an old cut off porpane tank as a solid chassis
      (approx 30cm=12" outside diameter) which should come down to pretty much the same dimensions you show in your drawing.
      Doing the math for the refractory ingredients and supplies I was only wondering about the amount of perlite:
      The outer dimensions of 11.25" diameter and 14.5" height takes me to about 1441 cubic inches (not considering the void space of chamber and hole in the lid) which should come down to about just a little less than 24 liters.
      You mentioned that you had about half of a 100lt bag of perlite left after the job was done so I was wondering where all that perlite went.
      Are you sure that was a 100lt bag or could that have been a 50 lt bag?

      Anyway - great projects, brilliant documentation and fantastic results!

      ...can't wait to chop up an ols cylinder head and get going myself...

      Looking forward to read about any new projects on your side - pleas keep it up this way!

      Beast regards


    3. Piter. I have checked and it was 100lt.There may be a bit more than half left but it defiantly used more than 24lt. If there is a 50lt bag that should do it.

  18. Thanks for all of your excellent video's! I have been watching, and re-watching them for months and can't wait to get my own furnace going. Your mould making skills are also amazing!


  19. Thanks for all the work you are sharing.

    are you going to use the perlite cement mix for the brass work? or will you use something else. i have seen others say that the perlite will melt at the temps needed for brass.


  20. Dave, No I won't use the Perlite mix for brass. As you say I don't belive the perlite or the fire cement would last very long at the higher temperature. The mix has proved exeptional though for aluminium, I have done hundreds of melts with it and it still looks almost as new.
    I have recently been given a Kasenit furnace and have just refurbished it but haven't actually melted in it yet. This will be my brass furnace. I hope to try it at the weekend.

  21. thanks mr myfordboy for passing on your knowledge, after finally building a furnace i managed to melt enough alum to get a couple of kilo ingots, it did take a good half hour per melt but i reckon i can fine tune it as time goes by, it'll be trial and error with gas and air mix, ventilation on the furnace and such like. this has taken me a good 4 months to get it all sorted as money is short and i'm also trying to convert my wood lathe to a metal lathe, i'm getting there so all is cool. so thanks again and keep up the superb work on the blog. ttfn from tetley

  22. Been watching lots of your video's and they are great.

    I want to build my own furnace for melting aluminium.

    Plan so far looks like using a 13kg sized gas bottle for the outer shell.

    Perlite and fireclay for the inner.

    I was wondering. Would an inner stainless steel or similar liner work?
    With the perlite between to insulate it?

    Ive not seen anyone do this. Would it take too much time to heat up? Must be a reason why its not done.

    Thanks. DRJ.

    1. Hi DJR
      The stainless steel would get holes in it from the burner.My stainless crucibles eventualy get pin holes and have to be replaced.
      Some builders use a seperate hot face of half an inch of a refactory material.

  23. So do the perlite mix as i planned then add 1/2" of pure fireclay for the inner wall?

    Or do the perlite mix, Add the metal ring inside then 1/2" of fireclay on that? Or will that just crumble and fall off?

    Just seen 25kg of rammable refractory on ebay just over £40 ready to use 1600C.

    Be a bit of a pain if i decide i need to alter the size for any reason and have to break it out though.

    Been scouring the kitchen isles at the supermarket looking for a decent thick walled stainless container.

    I dont want to spend too much, Just in case its a one off.

    Thanks for the help.


    1. DRJ
      Forget the metal ring. My furnace just as the perlite and fire cement mix and just a thin coat of fire cement on the inside just to smooth off the finish a bit. No problem for melting aluminium, has withstood hundreds of melts.

  24. Me again, What a minefield. I notice you use cement where others seem to say fireclay.

    Fireclay seems to be cheaper. Is this an option? Or is there a reason you used cement?

    Thanks for your time.


  25. DRJ
    It's not cement like you would use to make concrete but fire cement, used to seal and repair flues and fireplaces.

  26. Hi Myfordboy
    Fantastic source of information, I am at present construction a furnace to your design but would appreciate advice regarding the ramming of the fire clay and perlite ,Should the refectory be rammed with a large amount of force making the mix dense or just applied so that it fills all the gaps? I have the opportunity to dome the inside of the furnace lid , do you think this would help reflect the heat source , or possibly be detrimental to the heating process .

    Thanks in advance


  27. Keith,
    To get it to mix I added a little water to the firecement so it was wet enough to coat the perlite, so it did not need ramming. It was like laying concrete. Some builders use poystyrene beads which burn away after fireing.I don't think there is any advantage in domeing the lid. The refactory is more of an insulator than reflective.
    I have a layer of ceramic blanket on my base now and that reflects a lot of heat.

  28. Will fireplace refractory cement work?will a 500,000 btu torch melt copper?Will 100% natural clay kitty litter work for the greensand?

    1. Kitty litter is fine but the fireplace cement will not be suitable for the temperature required for copper. The burner though should have plenty of heat.

  29. Thanks for your quick response on kitty litter and 500,000 Btu torch do you have any suggestions on what I could use to build a foundry just like yours but hold up to copper melting and what kind of crucible to the way the torch is just a fleet farm grass burner torch that says on the package it will burn that hot

  30. You need a commercial refactory to line the furnace but I understand that copper is very difficult to cast. Brass or bronze is easier.

  31. Could you please explain why copper is so hard to cast and what I will need to make a successful cast all info given is appreciated highly thanks

    1. I have only cast copper and brass so cannot advise but here is something you could read.

  32. Could you please give me names of refractory cements to look for and possibly store that sell it in the USA or a good brand to look for and will your stainless crucible hold up to copper melting thanks I appreciate all the help you've given me so far just need these questions answered to starts casting so please help thanks

    1. I am in the UK so can't realy advise on a US supplier but I belive refactory may be available from Ebay sellers. A graphite crucible would be best for copper. A stainless one would not last very long.

  33. Few delays. But im almost ready. I think?

    100L Perlite. 25kg of KOS Fire Cement. 15kg Gas Bottle (Empty).

    How do you measure the fire cement and perlite? I imagine this will be hard work to mix properly and will need to do it in small chunks.

    Any idea how i can build it so that i can alter the internal dimension
    for different sizes of crucible?

    Or is that going to be difficult? Will a 2" thick brick of these materials be too weak?

    Many Thanks for your help.


  34. @DJR
    I used a small plastic tub and filled it with perlite. Tip 4 measures into a bucket. Add 1 measure firecement. Add a little water and mix as mentioned in the instructions above.
    I can't see how you can make an adjustable size furnace. 2" refactory is fine. There should be about an inch around the crucible wall minimum.

  35. Not too sure myself about the adjustable part.

    Just an idea. Its 12" across and 15" deep without the lid.

    My trial stainless crucible is just under 4"

    So not a huge way off the size of yours. I was thinking if i made
    a 2" layer on the wall of the cylinder and then 2" bricks that can
    be inserted or removed.

    Maybe thats too much for a 1st attempt.

    Just noticed your top exit hole is 4". I didnt cut mine that big.
    Looks like i may need to alter that.

    How much of a difference does the bottom vent hole make to the burn?
    Too big/too small?

    Is it worth making a small vent door for it? Spring operated so anything falling on it will open it or maybe a wire operated one?

    I had a vision of measuring the clay and not being able to get it all out of the tub making a mess and not the right ratio.

    So eager to start mixing and filling it up. But resisting that urge until all the holes are made. And trial fitted it all.

    Thanks for your time.


  36. @DJR
    I wouldn't wory about the adjustabe part. I have used a range of stainless crucibles without problems. The hole at the bottom was just to let metal escape is your crucible gets a leak. I made mine too small and it filled up with metal and is now blocked, makes no difference to the operation. The kasenit furnace mentioned in the description has no hole. I put a lining of ceramic insulation on the bottom now, if I get a spill I can tip up the furnace and let it out whilst still hot, Take care though!
    I expect you were aware of the dangers of cuttin up a gas bottle but mention it so others can take note.

  37. Yeah the bottle had been standing for 24 hours with a peg holding the valve open. Then i removed the valve and its been filled with water for a week.

    Emptied it and refilled twice more, Then left upside down for 48 hours.

    Only then did i take the grinder to it. Even thought its cut open and outside, I still get the odd whiff of gas. But i read the smell stains the metal and lasts for ages.

    Finding containers the right size is a pain.

    Possible i may made them out of cardboard and fill with sand to help it stay in shape?

    Is a 3" top hole too small?

    Thanks. DRJ

    1. @DJR
      I would think the cardbord would work. How about wrapping in clingfilm for a smooth surface finish?
      My hole is 4",I would enlarge yours if possible.

  38. thanks it is a big help. i face problems using printer but you helped me out. thanx
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  44. Hi
    Thanks for your site, I've enjoyed a lot of hours watching the videos and learning about casting/machining. I've even put some of it into practice!
    I have made your simplified gas burner to use in a furnace I built a few years ago and have used with charcoal. I am having trouble with the burner blowing itself out at rather low flame strength. I saw you need a flare to use it outside of the furnace - would a flare help with this problem inside the furnace? Also, the tuyere in the furnace is 50mm diameter and the burner 22mm diameter. Should I close off the tuyere around the burner? I ask because I saw you have a furnace with an extra air inlet. I have tried with it roughly blocked up, I thought this maybe made the flame go out easier.

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  46. Hi,

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