Introduction: How to Make a Small Gas Furnace
Why is it that all the things i make involving heat are small?
There's the coal forge, that was fairly diminutive, but i digress.
by-tor the snow dog asked me if the coal forge got hot enough to do glasswork. ( https://www.instructables.com/id/EG8B14NNJJEYMW0DC9/#CEXLBVSRGSWEZ7BDCQJ ) Basically, it does, but i wouldn't recommend it, because the hot coals will stick to the glass ans it'd be manky, so i decided to make a clean, hot-burning furnace using what i had lying around.
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Step 1: Get the Stuff
The first step is, as always, get the things you'll need.
I used the Refractory glop i sued for the coal forge -i'll keep using this until i find something better, IF i find something better- and a can. The can should hold about half a kilo and, even with the refractory taking up some of the space my torch was still struglling to heat all of it up, so if you want a bigger hotspot, you'll need a bigger can,obviously, and more torches for the heat, but that presents some new problems because you don't want the torches to overheat one another. This can held 540 grams of grapefruit. Because the can has to be emptied first, choose something you'd like to eat. If it's beans, work outside.
Step 2: Make a Hole in the Can
The can needs a hole, through which goes a pipe, into which is inserted the blowtorch. This is a bit like the blast pipe for the coal forge, but instead of blowing air through to fuel a fire, this is where the heat comes from. a chisel and some pliers are all you really need, the hole doesn't have to be precise, just big enough to fit a bit of pipe in. (don't use glavanised steel) Once you've made the hole, cut a length of tube or pipe about 2 inches long. Under no circumstances should the tube obstruct the torch's air holes. If this happens, the fuel mixture will burn too rich and you'll get crabon monoxide poisoning instead of heat. The effects of carbon monoxide are cumulative, each does gets piled on top of the last. The pipe should protrude about half an inch into the can, offset from the top by about 30 degrees. The picture should hepl you determine what it needs to look like.
Step 3: Add the Refractory
This is the easiest step, though it needs you to get your hands dirty. Using a spoon or a knife or your fingers, coat the inside of the can with refractory. Make it fairly smooth, too, this will make sure there are no nasty eddies or swirls inside the can that can do unpredictable things. The refractory should be between 1/4 and 1/2 inches thick. Mine was somewhere between those. Don't obstruct the pipe!
Step 4: Some Quick Notes
For those people who can't get XL refractory clay, there are others, more available and less available. The cheapest one i can think of is Adobe. This is simply a 50-50 mix of sand and clay. (no pebbles or rocks) Mix the sand and clay and apply them immediately, then let them dry completely before firing the adobe. After it's been fired once, it's ready for use.
Anyone living near a ceramic supply house or brickyard should be able to find something that'll do the job.
Step 5: Fire It Up
Once the refractory's ready to be used, use it. As with the coal forge i posted, i recommend that you fire it up without doind any work at least once, just to get a feel for it. Place the torch into the pipe making sure that the burner head of the torch doesn't protrude into the main area of the furnace. For god's sake don't obstruct the airholes. Also, don't even USE your torch if it's in anything other than perfect working order. To light the torch in the furnace, turn on the gas slowly while holding a burning stick, or a bit of rolled up paper with the end on fire in front of the burner. Once it catches, wait a minute or two till it gets up to working tempertaure.
Step 6: Making Stuff
My thanks to Larry Zoeller, of Zoeller forge for giving me the idea for this. The link leads to a similar one he made that geve me the idea to make this.
This furnace was designed and made with glassworking in mind, it's like one of the furnaces i used when i went to The World of Glass in St Helens to try glassblowing. There's no reason not to make small forged items in it, though, like arrowheads, but that might necessitate some small adaptations. There's no question about it getting hot enough, certainly.