Metalworking: The Gingery Furnace

The Gingery Furnace

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Dave Gingery has written a great set of books that describe how to build some pretty decent metalworking tools from scrap. If you are interested in metalworking, but don't want to spend a lot of money, get these books! They are available from Lindsay Books.

The first book describes the construction of a small charcoal fired blast furnace, which is then subsequently used to make the castings to build the machines.

The best thing about this furnace is that it is incredibly cheap to build. And pretty easy too.

I build a "by the book" Gingery furnace (charcoal fired, with the standard Gingery lining) and I'm really happy with it.

The hardest part was finding the components - the books were written a while ago, and some of the stuff is a bit hard to find. Here is where I found my stuff:

The 5-gallon pail: these days it's pretty hard to find a metallic 5-gallon pail - about the only thing I found that comes in these is roof tar. All the credit here goes to Bill, who was the first to discover (and use) a beautiful 5-gallon stainless steel stock pot from WalMart.
Fire clay. I had a little trouble finding that. Pottery places I called or visited seemed to think that "raw materials" mean unpainted pots, and ceramic / clay places wanted me to get real specific about what cone I was going to fire the clay at, etc. Finally I went to the local construction materials company. And sure enough, they had generic fire clay, powder form, no questions asked. Perfect.
Sand. Silica sand is the only thing that was easy to find. Home Base sells Silica Sand in 100-lbs bags.

11/18/2000 - Construction

I prepared the refractory mix a couple of days early, as the book recommends. I can vouch that following the instructions to the letter yields a pretty good lining: 5 gallons of sand, 2.5 gallons of clay, 3 quarts of water. I ended up with about 1.5 gallon of leftover, because the WalMart stock pot is a bit more squat than a standard 5-gallon pail. But that's OK, because I will later make green sand with it (by adding more sand) - same components, different proportions.

I was a bit surprised to notice that dry sand and clay don't mix that well after all. The clay tends to pool in the corners of the tub. I ended up putting on gloves and mixing the thing by hand, after adding water too. This worked very well.

Bill recommended that I "shape & bake" a sample, to see how it behaved. That was a really good idea, because it made me realize that the thing must be packed really hard to have any structural integrity.

The Gingery lining is basically a kind of fire clay. It's important to pack it well, and to cure it well, otherwise it is fairly crumbly and won't hold at all.

I wanted a pretty good fit for the air pipe, so I cut the hole in the pot this way: after cutting the pipe at the correct angle, I traced the outline of the hole and drilled through the center of the outline with a 1/2" bit. I then used a jigsaw with a metal blade to enlarge the hole, but still staying within the outline. And then I finished with a file, until the air pipe fit in there.

Here is the furnace with the form in, ready to pack.

The lid
My wife found a pretty nice steel pot to use as a crucible.

Of course I had to remove the handles, and I realized I could use them for my lid.

It was a simple matter to bend them to the right angle, and attach them to the strip with sheet metal screws.

To make the lid, I didn't use a form like the book says, but simply wrapped the sheet metal strip around the bottom of the pot, then built the wire frame.

After that I removed the assembly from the bottom of the pot, and it kept its shape pretty well.

Packing the lining
It's very important to pack the lining pretty hard. As mixed, it has quite a bit of air in it. I pounded it a bit too hard in the pot however, and the inside form started to give way.

Now the inside section of the lining is vaguely octogonal. It doesn't seem to have affected anything though, except that I really had a hard time pulling out the bottom disk for the form.

Another difference from the book is that I laid down the bottom layer of lining first, then inserted the form and did the sides. It's a bit easier, I would think. Most people seem to do it that way.

The Gingery lining must be kept wet until fired, which makes removing the form itself and the air pipe pretty easy. Apparently it's a lot harder when you use a refractory cement mix.

My last action of the day was to put the lid in the oven, covered with a wet cloth, ready to fire in the morning.

11/19/2000 - Firing

Curing the lining is a whole day thing - I started by turning on the oven to 250 at 6am, then moving up to 550 at 8:30am.

Here is the furnace, all set up and ready to fire. Picturesque, isn't it? What can I say, this is California.
The blower is a small vacuum cleaner, the hose is taped (with paper tape, so any reflux will burn through and out instead of into to plastic hose) to the air injection pipe. For the initial burn I plugged in the vacuum with an X-10 dimmer module and controller - the vacuum by itself would pump way too much air.

At 2:30pm, I turned off the oven (but left the lid in there) and started the charcoal fire in the pot. Lighting the charcoal was pretty hard, there is no draft at all in the pot when the air is off. I finally turned the air on very low. That did the trick.

When the charcoal was lit, I took the still-hot lid out of the oven and put it on the pot (thank God for welding gloves!) and gradually increased the air.

I was pretty concerned about getting it really cured, so I kept adding charcoal. The burn ended up lasting about 90 minutes.

At the very end (you can see it was pretty late) I put on the last bunch of charcoal and turned the air on full blast. I got this very nice flame shooting up. Some spots of the lining started glowing red, so I figured it was probably pretty dry at this point.
When it seemed that most of the charcoal had been burned, I turned everything off, covered the holes with brick, and called it a day. As it turns out, it seems that the rest of the unburned charcoal slowly smolders away after that. 14 hours later, after a whole night outside, the pot was still hot.

The lining got really hard and reddish where it was hottest (i.e. the inside of the pot, and the bottom of the lid) with some traces of vitrification (darkish, semi-translucent areas). The parts that did not get heated up very well (like the air inlet, and the top/outside portion of the pot) are quite a bit more brittle.

The lid finished curing during the firing proper - the temperatures reached in the oven were probably never enough to really cure it, but the firing did the trick.
A few cracks appeared on the lid during the firing, but they are very fine and fairly shallow. They don't seem to have affected the structural integrity of the lid.

This is the bottom of the lid. Notice the change of coloration from the firing here too. The reddish portion is much, much harder.

Next episode: casting.

Comments

Dear sir I would just like to ask you if you could tell me what kind of sand did you use. Was in the smooth beach sand, or was it somewat rougher. I would also like to ask you how ling did the furnance last? Thank youð
---- Rok -- rok.capuder@siol.net 08/09/2003

My \"local construction materials\" companies (Home Depot, local lumber-plus-other-stuff, etc) haven\'t heard of fire clay. Nor has the mason I called up, though admittedly he was more of a stonewall mason and not a fireplace guy.
Anonymous 11/05/2003

I used silica sand I got from Home Depot - which is pretty rough, definitely too rough to make decent casts. But it worked perfect for the lining. The furnace is still there, after 3 years, although I haven\'t used it as much as I\'d like to...
---- Denis Leconte 12/20/2003

For the fire clay, I actually went to a construction materials and landscaping company, the type that also exclusively specializes in things such as landscaping stones, concrete stuff, and bulk materials such as sand and gravel. Home Depot is a bit too general to have fire clay.
---- Denis Leconte 12/20/2003

Very interesting, I hope to build the Gingery Furnace too. Thanks for your help.
---- Charles Fenech -- sphynx@nextgen.net.mt 06/25/2005

Hi, I am looking around for materials to build a small charcoal furnace, but I am having trouble locating Fire Clay, I live in the UK, you are in the US I guess? So if there are any guys this side of the pond who know where I can get the stuff, I would be much obliged. Best regards Bob.
---- Bob Cable -- bobjcable@hotmail.com 12/12/2005

Hello I woud like to know are their any other meterials you can use besides fire clay like cement or is that the only thing their is to use
---- Brenden -- hot888xxxx@yahoo.com 01/11/2006

Some people are using a blend of furnace repair cement (easy to find but expensive) and perlite (dirt cheap in the gardening section. Just enough cement to hold things together, like 4 to 1 perlite.
---- triticale -- triticale@hotmail.com 04/03/2006

it woul d be much nicer to use gas, u would have better control good luck guys
---- adie fnaishe -- adie@batelco.com.bh 04/14/2006

i found firclay at a potery class 4 hobyists .my foundry has 20 or more melts over 8 years.i plan on starting on the lathe in july 06.
---- art whitney -- smokingluves_422yahoo.ca 06/25/2006

sorry abt.the email address just lernin\" howto work a computer.
---- smokingluves_42@yahoo.ca 06/25/2006

can you tell me the difference between fireclay and refractory cement . i am building a fireplace and am unsure as to which to use between the firebrick of the fireplace
---- len loza -- lenzo50@aol.com 10/21/2006

I read bobjcable@yahoo.com comments (and other commenters). Well, in fact I suppose that in various States of the Much favoured by me USA, that access to suppliers by people who live in various states of this fine Country is not as easy as we Brits may seem to think due to the sheer size of this country! But BOB, There is a supplier on your door step (relatively speaking) and is as follows; ENGINEERING AND FOUNDRY SUPPLIES, PHILLIPS LANE WORKS, COLNE, LANCASHIRE. U.K. Tel. +44 (0) 1282 868411 Fax +44 (0) 1282 867545 http://www.ef-supplies.co.uk/foundry_equipment.cfm I(without seeming to be self important I hope) can say that I have much experience in Engineering \"hands-on\" and theoretical. I spent 10 years as a Garage foreman 10 years as a toolmaker and some years metal founding in cast iron production and some years as a milling machine setter/operator and leading hand macine line setter on gear cutting, plano milling and precision machining of aircraft components. Also I hold a National Certificate in Plant Engineering, an I am a fully licenced Radio Ham and member of th Radio Society Of Great Britain ( and I used to Build radio valve (in America TUBES) equipment as a hobby.Let me say at this point that the greatest INOVATORS that I have EVER come across have been the so-called \"unskilled\". Professor Eric Laithwait had it spot - on when he said \" Whatever ideas that you people think of the beleive in what you do and take no heed of people that laugh at your idea\" or words to that effect in his Royal Institute Christmas Lectures. Was not Einstein told that he was USELESS at maths!?
---- Bill Jackson -- wiljack@tiscali.co.uk 11/23/2006

Having just read my own diatribe I missed the point of what I was meaning to say, and it was; Try GANISTER it resists the heat of molten Cast Iron and usually is used in furnaces Over Fire-Brick ( but experiment with it!) and No_one in all of the various different articles that I have read seem to mention the use of Silver Sand which is mixed with a tar-like substance that I have forgotten the name of which when shaped easily into moulds is then GASSED over the open surface of the Mould and hardens like Steel and is ofcourse discarded after casting as spent. Don`t forget BELLS were cast using a mix of sand, coal dust and COW DROPPINGS and the great bells of BIG Ben are still cast this way to this day, as were Cannons in EUROPE AND AMERICA---Just a thought----BYE.
---- Bill Jackson -- wiljack @tiscali.co.uk 11/23/2006

Add a comment

	My wife found a pretty nice steel pot to use as a crucible.
	Of course I had to remove the handles, and I realized I could use them for my lid.
	It was a simple matter to bend them to the right angle, and attach them to the strip with sheet metal screws.
	To make the lid, I didn't use a form like the book says, but simply wrapped the sheet metal strip around the bottom of the pot, then built the wire frame.
	After that I removed the assembly from the bottom of the pot, and it kept its shape pretty well.

	It's very important to pack the lining pretty hard. As mixed, it has quite a bit of air in it. I pounded it a bit too hard in the pot however, and the inside form started to give way.
	Now the inside section of the lining is vaguely octogonal. It doesn't seem to have affected anything though, except that I really had a hard time pulling out the bottom disk for the form.

	When the charcoal was lit, I took the still-hot lid out of the oven and put it on the pot (thank God for welding gloves!) and gradually increased the air.
	I was pretty concerned about getting it really cured, so I kept adding charcoal. The burn ended up lasting about 90 minutes.
	At the very end (you can see it was pretty late) I put on the last bunch of charcoal and turned the air on full blast. I got this very nice flame shooting up. Some spots of the lining started glowing red, so I figured it was probably pretty dry at this point.

	The lining got really hard and reddish where it was hottest (i.e. the inside of the pot, and the bottom of the lid) with some traces of vitrification (darkish, semi-translucent areas). The parts that did not get heated up very well (like the air inlet, and the top/outside portion of the pot) are quite a bit more brittle.
	The lid finished curing during the firing proper - the temperatures reached in the oven were probably never enough to really cure it, but the firing did the trick. A few cracks appeared on the lid during the firing, but they are very fine and fairly shallow. They don't seem to have affected the structural integrity of the lid.
	This is the bottom of the lid. Notice the change of coloration from the firing here too. The reddish portion is much, much harder.