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Part #3 of building my Deep
Throat Furnace.

Making the molds and pour the Refractory.

Well; I'm finally back; got hit by a nasty virus and then right after I got that fixed my Internet died. But that gave me some time to go down in the 'dungeon' and work on the furnace.

OK, Let me start out with one of my tools and some of the supplies I use to make the molds.

This is my hot wire foam cutter... was simple to build with scrap lumber and most parts you can get from places like Radio Shack. The NiChrome wire I got off of eBay.

hot wire cutter

In this shot it shows how I cut circles. The first hole is at 1" and a the rest are a half an inch spacings. I think I'm using a roll pin of 1/8"X1". I 'had' several shots of the top mold, but I'll be dammed if I can find that disk now.

pin for cutting circles

Here's is the back and this is how I can do angles or taper cuts.

back of cutter

And this is the power supply... I got the circuit from the web some years back and don't remember where. I guess I better do some more searches and find the info and make a page on how to build this foam cutter.

power supply for cutter

Next is just a few of the filler puddies I use.

puddy and glue used

Next are the spacer sticks I make up to keep the molds centered while you're packing in the refractory.

Starting from the bottom I glue two sticks side-by-side, then cut them length wise to get the spacing, (In this case I want to have 2" wide spacers), now I take the cutoff piece and glue it on sideways, This gives it a wider base to stand on.

paint sticks made into spacers

OK, now as I said I lost the disk that had all the pitures of the top mold, but it's basically a 5-1/2" by 6" cylinder made from 2" thick foam and glued together with white glue. A circular notch is cut in for the burner tube. You probably can figure this out when you see the finished top section.

Now the main body mold is a little more involved and a lot more work.

What I had to do was make a cylinder 5-1/2" in diameter and 18" tall with a closed bottom. It was a toss up: "Do I make it out of foam or wood or cardboard?"

Well after hunting around I found some concrete post forms that were close to what I needed.

concrete tube size

Now this is some tough stuff, it has to be if it's gonna hold back a column of concrete.

So I cut it about 4" longer then my finished length then cut it length wise. Now the work starts as I try to roll it down to that 5-1/2" dia., so I cut some 1/4" hardboard and used very big hose clamps to pull it into shape.

Now the next problem was what to glue it with that could take the pressure as it was trying to spring back to that 8" size. I tried everything on the shelf... think it was finally a combination of supper glue and 5 minute epoxy along with a those clamps.

clamped mold

2nd. view of clamped mold

After it had dried a few days it was time to close the bottom, (which would help hold it's shape).

cut tabs to make bottom

I started by cutting 10 tabs then taper cut them as I bent them over once they matched I would glue the two tabs together and hold it in place with a spring loaded paper clip, (Used big bulldog clips at first).

cut up pizza box to cap bottom

Next I got out the old reliable pizza box and cut an end cap and glued that in place over the tabs.

plastered mold

Now I coated all the bents and dings with Plaster of Paris mixed with white glue, after sanding that down I use the glazing puddy to fill in the small spots and again sanded that down. Then a heavy coat of primer paint, (sanded), and three coats of gloss paint, (All sanded as well) then one final finish coat.

finished painted mold

OK!!! We're ready to pour the refractory.

(NOTE: See my page on how to make and mix refractory),
Lets start with the top lid.
First you add in about 2 to 3 inches of refractory, then settle/wiggle in the mold, (now comes the hard part), with the six extra hands you DON'T HAVE; you have to hold the mold in place while inserting the spacer, which don't want to stay where you put them.....

top with spacers

top view of spacers

close up of spacers

Now many of you will notice that the mold is leaning back a little -- my fault -- when I took out the spacers after filling it up the mold twisted off its mark, plus I was ramming the front harder and more often than the back.

Fortunately it wasn't bad enough that I would have to dump it all out and start over.

top with refractory

another view of refractory in the top lid

top lid after mold is burned out

Now once you're done 'over filling' at least a 1/2" above the furnace wall you can finally relax for several days... DON'T TOUCH IT! Let it dry for at least two days.

Now how do you remove the molds without damaging the refractory??? You burn it out! The easiest is the top as the foam just melts away with a propane torch, but the cardboard tube was another story... even with all those coats of paint the water still soaked thru and I had over an inch of water in the bottom, so grab a big can of charcoal lighter fluid and squirt down the wall and let it soak in then do it again, then lite it off, but you might have to do it a couple of more times.

Another thing you might want to do is take a box knife with the blade just a 1/4" exposed and cut vertical slits all around the wall.

Once you get the mold out go get the 'better half's' hair dryer and let it run for a few hours, (OR until she finds out what you've done!!!)

burning out the mold

front view

Back view

You see the dark spots towards the bottom and how the bottom is a dull gray as compared to the white of the top half -- that's still wet after a week and that's with 10 'controlled' low temp heatings.

Read my page on the proper way to dry out the refractory

Top view



Now on to Part #4 ... custom fitting the lid to the body and making the
platform to mount the furnace on.

Back to Foundry Page
Back to Building Part One
Back to Building Part Two
On to Building Part Four

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