My first Furnace


Click on any image to see a full size picture.

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First flare the gas from your chosen propane tank.
Getting an empty one in the first place helps greatly.

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Once its empty, unscrew the valve from the top & steam it out.

I did this by putting a pint of water into the tank and I heated the underside with my burner to boil the water off.

This removes any residual propane.
It doesn’t smell too nice though.

Now cut the top off with an angle grinder or hacksaw.

Cut a hole in the side for a burner & one in the top for an exhaust.

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Burn a hole in the bottom.
This is to allow an escape route for molten aluminium if the crucible fails.

I welded up the crucible from scrap hydraulic pipe at my college welding course.

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Now find something that when inserted into the tank will give you a clearance of 2 to 3 inches.

The coffee cans I chose were not broad enough so I wrapped cardboard around them to reach my desired diameter.

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The finished ‘form’.
I didn’t trim off the excess cardboard as I wanted something to get a grip of later to pull the form out.

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A quick test fit of the form.

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I’ve now inserted a pipe through the burner hole to guage where to level the floor of the furnace.

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As you can see…

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… I’ve guesstimated the burner hole a little low. I’ve left myself a bit short of space for a layer of refractory in the bottom of the tank.

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Make a T-piece of wood…

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… so that the top part is the width of the form & the bottom part is just long enough to make the surface of the top part level with where you want the floor of your furnace.

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You will need

Building sand
Perlite
Fireclay
Portland cement (not shown)

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I have used 4 litres of Perlite to 2 litres of sand,
2 litres of fireclay & 2 litres of cement.

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I mixed it with water applied with a sprinkler until I could created a ball of mixture which would not fall apart on its own.

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Fill the bottom of the tank by hand & tamp the mixture around the wooden form.

Insert the main form & ram the mixture around the form using a suitable piece of wood.

Sadly, I made far too little mixture & I only managed to fill the tank less than half way. It was getting late & I had to call it quits for the night.

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The next day, I mixed up another batch with the remaining 5 litres of perlite.

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It still wasn’t quite enough. To hell with it. I’ll just make the insulation in the lid deep enough to fill the gap.

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I waited till the next day to pull the form. I cut holes in the top of the form to give me something to hold onto whilst pulling it out.

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Here’s the uncured refractory. You can see the wooden form at the bottom. When it burns out it will leave an escape channel.

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I filled the furnace half way with good quality charcoal & lit it up. I hadn’t made the lid by this point so I just used some insulating bricks.

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After the charcoal burnt out I inserted the propane burner.

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It looked hot enough to melt so I put in my crucible & a small piece of scrap aluminium which melted readily.

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I had prepared a simple mould by shoving a socket extension bar into a tin of oil bonded sand.

Sadly, due to my excitement, I dropped the crucible onto the concrete below. I beat a hasty retreat as the concrete popped & banged, throwing molten aluminium into the air.

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You can see how the concrete spalled under the aluminium.

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Not a total disaster though. I did get some aluminium in the mould.

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Here’s the furnace after it had cooled.

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And here’s my first casting.

It may look pathetic but it is merely the first step in learning a new skill.

Improvements… a lid and a new burner>

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The next thing to do was make a proper lid. I have raised the level of the wall of the rim in order that the refractory will sit proud & fit into the rebate in the furnace refractory.

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Here the wet refractory is in the lid & I have made a vent hole in it with a thin glass jar (not shown).

Any cylindrical object of the right diameter would work.

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I have made a Bunsen type burner from plans on
Cameron McKeowns page

The main jet is a Tweco mig wire tip of 0.8mm diameter. The flow rate is badly insufficient as you can see that the movable choke on the burner is almost fully closed. Opening it causes the burner to go lean & flame out.

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I have bored one of the tips (I bought several) to 2mm.
Why 2mm?

Because my 1.5mm drill snapped off in the previous tip I tried to drill.
I will try to make a 1.5mm jet soon though, as even with the choke fully open I still cannot get complete combustion with the gas full on.

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Putting the lid on doesn’t help either!

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This is it running at about 15psi.

Zero to zorch in under a second.

Patently major overkill for this furnace.