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Part #4 of building my
Deep Throat Furnace.
-Shaping down the Refractory -
-Doing Dozens of Burn-ins -
- Making the Mounting Platform-


Well it's “Finally” finished and
the first pour has been done.





OK, The refractory is now dried enough we can start the task of shaping the top and bottom to match.
As You can see how high I built it up.











Here you can see just how much I have to shave/cut out to bring the two together.




Now the idea is to keep the top radius as much as possible and shape the bottom to fit the contour, making a better seal; and make no mistake; This is a lot of work and it takes a lot of time cutting/grinding/shaving just a little at a time.



Now the next question is: “Once it gets close; How do I see where to cut/shave”?

Well that can be done in a couple of ways.... (HOT OR COLD)

THE HOT METHOD:

You have to start drying out the furnace any way, so you fire it up and see where the fire comes out.

The only drawback is you now have a hot furnace to work on, but this is what I had to do when it got to a really close fit.


THE COLD METHOD:

Go to Home Depot/Menards/etc. and get a 'construction' light socket, (it's a rubberized lightbulb socket with just two wires coming out of it.) attach a cord to it with wire nuts and use a 60 watt light bulb put it in the bottom of the furnace and run the cord out the spout.... plug it in and close the lid.... now you'll see the gaps and all the high spots.







TOOLS I used for shaping the refractory:

  •  a coarse wood rasp (Half-round and Flat)
  •  80 grit sand paper (by hand and on a block)
  •  a thin flexible blade saw (Used for scrapping not sawing)
  •  die grinder (Tapered and ball end)
  •  80 grit flap wheel on a 4” angle grinder



Now here's my first warning:

That flap wheel will cut thru the refractory like it's hot butter; You MUST use a very light touch. The die grinder is less aggressive, but can still dig in, so run that at a low/slow rpm.



After many hours of grinding/filing/scrappings plus about 25 heating/coolings here it is RUNNING at full power. (The camera flash killed the nice blue flame coming out.)



Now with this type of furnace the only exhaust port it has is out the spout, so if your furnace start rapping off like a machine gun it means that the opening is not big enough. Shortly after I took this picture it started, so I had to go back in and cutout about a 1/2” in the top lid and then taper the refractory back away from the spout. During the first pour it started doing it again and what had happened was some slag got caught in the spout. Cleaned out the slag and it was back to normal.









Now that the furnace is done I need something to mount it on and I kept thinking about the different mold sizes and heights I've worked with, that's how I came up with this platform.

I took a couple of 2 X 6's and cutout the pattern (pic. on the left). Then formed and notched out a 12ga. sheet to match. (right)

I then epoxied the two together and clamped them down over night, the next day I finished off by using 1-1/2” drywall screws. (The sheet metal is not only to reinforce the support arms, but also acts as a heat shield from the furnace.)

 



    


The platform base is simply a 1/2“ exterior plywood 4 X 8 sheet with a gallon of polyurethane on both sides for a weatherproof coating. The frame is made up of 2 X 6's. (You can pour your molds on the surface because the sand insulates it, but you need to put your pans/ingot molds on top of fire bricks.)





Where the support arms/posts are attached I reinforced the bottom with a 2 X 6 laid down flat against the deck. Everything on the frame was put together with 2-1/2“ and 3-1/2“ drywall screws and for the support arms I used 4“ and 6“ lag bolts.





I've learned a lot from my first pour, as I've said before “Every furnace has it's own character trates.”

Rule #1: Never run the furnace of it's 90°+ outside. "DDDDAAAAHHH!!!"

Rule #2: Preheat for at least an hour. (Because the pot is so deep the standard 20 minutes won't be enough.)

Rule #3: You had better spend that time prepping a lot of alum.

Rule #4: Skim off the slag each time before you add the next load of alum. (I didn't do this and wound up with cold spots and it took a lot longer to heat.)
















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