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Furnace

After researching numerous websites on home foundry, I've decided to go with a slightly modified Gingery Crucible furnace.

The modifications include:

* 14" Diameter oil drum for furnace body
* Slightly oversize frame to allow for the larger body
* Propane Monster Burner

10/30/04
I found an oil drum at the local scrap yard.

drum01.jpg

While picking up supplies at the Home Depot, I had an idea for cutting the drum into the various sections of the furnace body. I decided to mount the drum on a Lazy Susan bearing and rotate it against a mounted angle grinder with a cutoff wheel. In theory this will create a fairly clean strait cut that will require only minimal cleanup.

I made a cardboard pattern of the body of my angle grinder then screwed two pieces of 5/8" plywood together, transfered the pattern and cut it out on the bandsaw. Since the grinder body was molded plastic, I estimated that it had about two degrees of draft, so I set the table on my spindle sander to allow for this. After several test fits, I finally had a cradle to hold the grinder flat and square. I used drywall screws to hold plumbers tape to strap the grinder down. For extra grip I slipped a piece of rubber between the grinder and the plumbers tape. All I need now is a fixture to hold the grinder at the desired height while I rotate the drum against it.

grinder01.jpg

10/31/04
I'm still trying to decide how tall to make the furnace sections. I think I'll stay with 6" for the base and 2-1/2" for the lid, but since the drum I have selected will allow the inside diameter of the furnace to be 9" instead of 8", I'm toying with the idea of making the center section taller to allow for a larger crucible. This presents two potential problems; first it changes the geometry of the lifting mechanism and second, the furnace body will have to lift higher so I can get the crucible out. I think I'll make a mock-up of the mechanism to make sure everything will work.

11/7/04
Today I decided to make a mock-up of the lifting mechanism out of 1/8" Masonite. I made all the parts extra long so I could experiment with different hole locations for the pivot points. I wanted to make sure I had the geometry right before I cut the furnace body from my drum.

Here is a shot of the Masonite monstrosity screwed to my molding bench. Note the Swiss cheese effect with all the trial and error of hole locations.

mock_up.jpg

Here is another showing the mechanism in the rasied position.
mock_up2.jpg

After some tinkering around, I got the mechanism to give me 12-3/4 inches of travel and lock nicely in the upright position. It looks like I might be able to use a #10 crucible or maybe larger. Gingery recommends using a #8 until you get the hang of things but I don't see the need to buy two crucibles. I can start with smaller castings and just not fill the pot until I see that everything is working okay.

I didn't really take any pictures of the construction of the frame and lifting mechanism. If you are interested in building a furnace you should buy the book "Building a gas fired crucible furnace" by David J. Gingery.

Here are some snaps of the nearly finished product.

furnace-frame-closed.jpg

furnace-frame-open.jpg

2/4/05
After a two month absence I finally returned to the shop to continue the furnace project. It was time to cut the oil drum into furnace sections. I mounted a plywood disk on the bottom of the drum then mounted the lazy susan bearing. Not being a precision bearing the whole arrangement was kind of wobbly. After some additional thought, I decided to go another route. I ditched the bearing and set the drum on my bench, which has a very flat top. I then built a plywood box to hold my cutoff wheel at the desired height for the first cut. This would form the lid for the furnace using the upper 2.5 inches of the drum and retaining the factory rolled edge.

I placed a half bag of play sand (still in the bag) into the drum to hold it tight to the bench then worked the grinder around on the box using the fixture I built back in November. I could cut about 5 or 6 inches then stop and rotate the drum. I did clamp the plywood box to the bench for rigidity. After the first cut I just cut down the box to the next desired height, clamped it back down and cut again. This worked unbelievably well! The cuts were flat and perfect. All I had to do was touch up the sharp edges with a file.

I forgot to take pictures during the process.  Here is one after the fact that shows the box cut down for the final pass and clamped to the bench with the grinder jig sitting on top.

cutoff-jig01.jpg

2/5/05
I drilled the holes in the body of the furnace to mount it to the lifting arms then mocked the parts together to see how it would look. The center section is bolted to the lifting arms. The base and top are just perched for effect.

body-on-frame02.jpg

Here is another one with the mechanism open.
I put a 24-inch rule in front of it for scale.

body-on-frame05.jpg

2/11/05
I started building all of the forms for lining the furnace with refractory. I had some 5/8 plywood left over from another project so I cut 14-inch diameter holes in two pieces to hold my drum in a round shape while ramming in the refractory. I also made the 9-inch forms for the bore of the furnace. I then shifted to cutting out galvanized roof flashing for the inner forms. I took my time and everything turned out nicely.

2/12/05
Today I drew up and cut out the transition piece for the burner inlet. I made some plywood disks to hold it in a round shape. I also cut the hole in the bottom section of the furnace to insert the transition.

burner-form01.jpg

It matches up with the inner form pretty well.
furnace-body-form.jpg

To be continued....

10/10/05
No progress. Since I last added info to this page back in February I have purchased a house and moved to a neighboring town. The house is great and the new shop is nice, although much smaller than the old one. I am still trying to get my tools and equipment put away and organized so I can start working again.

9/28/08
Well, I have tackled several new projects since I moved into the new place but it's time to get back to furnace building.

9/28/08
I had been thinking I would a use commercial refractory rated for 3000 degrees F.  This way I would be able to pour aluminum, brass, or iron if I ever wanted.  With refractories, there is a trade off between high temp and high insulation value.  Lower temp. refractories generally have greater insulating properties and are lighter in weight.  What this greater insulation means to the backyard metalcaster is faster melt times and lower fuel consumption since less heat is being lost through the lining.  As I scanned the vendor sites looking at the specs, I decided it is unlikely that I will ever want to melt iron in this furnace and that I would be better served with a lower temp furnace lining.  To acquire this would require a trip to a foundry supplier in Kansas City.  With the high gas prices I try to limit my driving to a minimum.   It's not so much that I can't afford it as it is a choice not to give my money to the thieving oil rich countries of the middle-east.

I was talking to a friend yesterday about metalcasting and it got me fired up about getting back to work on the furnace.  He has built a Gingery charcoal furnace and used it to build several of the machine tools in the series.  His furnace uses a homemade refractory that has worked well for him.  I decided that since I already had everything I needed to make my own furnace lining, I would go ahead and make it.  When it wears out I can think about commercial refractory.

I will be using the following recipe from Lionel Oliver at www.backyardmetalcasting.com

2 parts silica sand
1.5 parts perlite
1.5 parts portland cement
2 parts fire clay

When I stopped work on the furnace I had all of the forms made, I just had to dig them out and start mixing.


I set the base on a plywood form with a round to hold the PVC pipe in place for the drain hole form.
After the lining is level with the top of the PVC pipe the second form will insert into the pipe.

The form for the burner opening.

This will provide a smooth transition for the burner to crate a swirl effect inside the furnace.

I didn't get any photos of the refractory mix as I was trying to work fast to get it mixed and rammed up.
Here is the base rammed full.

I covered it with plastic and let it cure overnight.  The next day it seemed pretty well cured so I decided to remove the forms and see what I had.  The bottom piece of plywood was pretty tough to remove.  I ended up turning the base on its side and using a length of 1" black pipe through the drain hole to drive it out .  Then I was able to just peel the sheet metal out of the refractory.

If you look closely you can just see the four wooden dowel rods radiating out from the center.  These will create slots in the floor that taper to the drain opening for better drainage if a crucible should leak.  I didn't try to pry these out, they should burn out when I fire the lining.  The PVC pipe is in there pretty tight too.  I will try to get it out so I don't have to smell it burning.


This shot shows how the burner hole transitions into the main cylinder of the base.  The lining looks really good with only tiny voids in the sidewalls.  The floor is very smooth.

After I took this photo I realized that my burner is going to get lost in that opening.   I followed the directions in Gingery's book but it was sized for his burner.  I may have to build a smaller form and pack some more lining material to make a better fit and to get better fuel efficiency from the furnace. 

10/3/08
 I worked on getting the main body of the furnace ready for this weekend.  I only had two circular forms for the outside to keep everything round so I decided to cut another one on the CNC.

With a ring around the top bottom and center, this should hold its shape pretty well.
I had this scrap left over from the outer form and decided to cut some 6-inch circles to use as a base for plinth blocks.  The CNC sure makes this easy and what would have been left over waste is nicely used up.

After some fancy band saw and spindle sander work I nailed dowel rods to each base to create a larger drain channel between the base of the furnace and the plinth block.  I guess I should mention what a plinth block is.  It is a loose piece of refractory material that sits in the bottom of the furnace and the crucible sits on it.  These will yield a 6-inch diameter by 2-inch thick block.
Here are the three finished forms.  If I mix too much refractory, I will have these on hand to use up some of it.

10/5/08
Last night I rammed up the lining for the body or center section of the furnace.  Between mixing the refractory and ramming it up it just about wore me out.  Thank God I didn't build this thing out of a 55-gal. drum.  Wait, I could probably get a #30 crucible in one that size.  Unfortunately, it would require 2 men to pour and three men to ram up the lining, so back to reality.
Here it is after I finally finished ramming in the lining. 
You can see the white flecks of perlite evenly distributed.
Oh crap!  The outer shell rode up out of the base form by about 7/16".


The good news is that it rose up pretty evenly all the way around.
I think I will just run it this way since trying to chip off the excess is probably a bad idea.
This is a view from the bottom.  With the center form out it looks really good.  The portland cement in this recipe gives it excellent green strength.

I wrapped the body somewhat loosely in plastic to keep it from drying out too rapidly.  I will leave it for four or five days then open it up to finish drying before I fire it.  I had planned to fire the base this weekend but didn't get to that or putting the lining in the lid.  As long as I continue to make progress, I will be happy.  I don't have to get everything done at once.
I was able to drive the PVC pipe out of the drain hole in the base and decided to see if I could pry out one of the drain channel forms.  Here you can see the tapered channel going to the drain.  The channels in the plinth block will sit over these.  The drain is only necessary if a crucible breaks to allow the molten metal a place to escape rather than solidify in the bottom of the furnace.

10/6/08
When I got home tonight there was a package sitting on the porch.  I opened it and took a couple of pictures or my new #10 crucible sitting on a plinth block in the base of the furnace.


This is the perfect size.  I was afraid the dimensions would look good on paper but the reality would be otherwise.
Another angle.

10/9/08
After a few days of drying, I decided to put the center section of the furnace in place to see how things were lining up.  I haven't weighed any of the parts yet but this thing is heavy.  The lifting handle didn't want to move at first but after a few shots of WD-40 and some working of the mechanism things are smoothing up a bit. 

A few more pictures.
The bottom of a plinth block showing the drain channels.
Looking down the barrel after the center section is temporarily assembled onto the frame.
Another shot with the crucible in place.

10/11/08
After checking the local home centers, hardware stores, and lumber yards, I couldn't find the right size bell reducer for the Monster Burner.  I got my local plumber to order one for me and it arrived this week.  I was able to find the other fittings locally and started on the burner this morning. 

Although I found brass pipe plugs for the orifice, I could only get them with a square head.  This left very little room for error in drilling the orifice.  Since the square was cast, I had to file the draft and get the sides parallel so it would sit straight and square in the drill press vise.  I didn't get any pictures of the build as things were going well and I didn't stop to get the camera.  

The burner after assembly.  The pipe is 14" long at this point.
The sheet metal choke plate swivels on a 10-24 socked-head cap screw with a conical coil spring holding tension against the plate.
A view inside.  I used 10-24 set screws to keep the 1/8" pipe fittings in place.
Regulator and gauge from Zoeller forge.

After building the burner, I decided to fire the base of the furnace. 



While waiting for the charcoal to get going, I hooked up the burner outside for a test run.  I set the regulator at 12 psi, inserted a long-nosed butane lighter in the back and slowly opened the ball valve to light it.  As I continued to open the valve, the burner made a fair amount of noise and produced an impressive flame.  Before I could open the valve completely, the flame would blow itself out.  I tried this many times at various pressure settings with the same results.  I decided I would cut some length off of the pipe and try again.  When it cooled off and I was marking for my cut I realized that I had not cleaned up the end of the pipe.  It had been cut at the hardware store with a pipe and tubing cutter that left the edge rolled into the ID.  I assumed that this had disturbed the air flow and probably caused my problems.  I cut the pipe so that 11.5 inches were showing outside the reducer.  I also filed the end smooth and cleaned up the ID and OD with a file.

I headed back outside and gave it another try.  The results were similar to the earlier trial.  I decided to try a new approach and reduced the regulator to about 8 psi.  I cracked the ball valve to light it and slowly opened it all the way.  The burner stayed lit.  I opened the choke completely and proceeded to increase the pressure at the regulator slowly until it reached 15 psi.  It stayed lit and produced a loud sputtering roar.  Rather than risk setting the top of my sawhorse on fire, I decided to call the test a success and shut it down.  It was hard to see the flame in the daylight so I will have to do more tests after dark to determine what type of flame it is producing.
The burner cooling off after its first successful test run.

10/12/08
Today I fired the main body of the furnace.  I wasn't really satisfied with the results I got yesterday on the base so I set the body on top of it and fired them both.  I started the fire about 10 am and didn't cover it until about 6 pm.  
At the scene of the hillbilly cookout.


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