A word of caution!

I missed something that I consider very important earlier on that goes back to mixing the refractory.

**When handling SILICA SAND, make SURE that you take care to avoid breathing any of the dust!!!**
It is not the healthiest of materials to be around and can cause severe health problems. I used a respirator when I was mixing up the refractory.

Curing

After getting the refractory liner in the furnace I left the furnace covered for several days. From what I have read this is ok to do, even possibly advantageous to do, as long as the refractory is not allowed to dry out. I had no issues when I finally got around to curing the refractory liner. Now, this is where having the lid ready to go is necessary because it is required to complete the curing, in fact when I made the lid I also took some of the extra refractory and made up several small bricks with the left over material and cured them at the same time by simply placing them among the coal of the fire for the duration of the lid curing process.
Curing the furnace is straight forward enough. I started with a double layer of charcoal, soaked in lighter fluid and got them fired up. I used this lower temperature heat to drive moisture out of the liner slowly and it also burned the cardboard inner form out as well.

After getting the first double layer of charcoal going good and burning out the inner form I added another double layer of charcoal and got that going strong. I kept adding charcoal layers as the last layer of charcoal was burning good until I had about 2/3's of the furnace filled with lit charcoal. Then I put the lid in place and started adding air through the tuyrere.

I used my shop-vac as an air source, which was a bit too much air. To solve this I am working on a valve system to allow a variable, more controllable flow rate. But as you can see, it worked great for the curing process.

I kept this up all through the burning of the first load of charcoal and when that had burnt down to a few inches left I added to the charcoal again to a load of about half full and kept the air going.

 

Use caution! As you can see the furnace will send out some embers, especially with a fresh load of charcoal (note how I have backed the air supply away from the tuyere to limit airflow)

I was surprised at how hot things actually got inside the furnace!

The furnace

After getting all of the various components in place and the refractory mixed I began to fill the furnace using a small garden shovel. As I would shovel in an inch or so of refractory I would stop and take the time to tamp the mixture into place, trying to make sure that all voids were filled. After I had gotten about half-way up the inner liner I pulled the alignment spacers hoping that the weight of the refractory packed in place to that point would keep everything in place. That seemed to work fairly well and I didn't notice any shifting around.
After getting the furnace all filled, I troweled the top smooth, covered the furnace with plastic and set it aside with plans to cure the liner within a few days.

Almost forgot!

I almost forgot a step in getting the furnace ready for use. It requires an air source of some sort to be able to crank up the heat necessary to melt metal. The temperature required to melt aluminum and tin or pot metal is relatively low so it shouldn't take much air to do the job. Gingery's book mentions a few methods one of which is to use a hair dryer. Being that I have plans to build a different furnace capable of melting cast iron I decided to try out a larger air source and design a method of controlling how much air is sent to the furnace. Either way a method of connecting an air source is needed and that is where the tuyere comes in. For the furnace this means that a pipe is added through one side of the furnace and into the inner chamber. The pipe will accept a slightly smaller pipe that will be inserted into the tuyere to provide the air. Dave's book calls for a 1 inch diameter thin wall pipe that can be split and opened up a bit to accept a length of the same 1 inch diameter pipe. I bought a few feet each of a thicker walled 1-1/4 o.d pipe and another piece of pipe that was roughly 1-3/8 i.d not perfect but more than adequate.

I located the tuyere roughly 3 inches on center from the bottom to allow for a decent depth of refractory to line the bottom of the can. 

Refractory Mix

Again, using a mix of 2 parts silica sand, 1 part fire clay and a minimal amount of water the furnace is ready to fill.

 

Setting the liner

And here is the liner and spacer set up:

Setting the liner

After getting the liner ready I needed to get it set into the correct place and keep it there as I filled the can with refractory. To take care of this I made up 4 spacers to hold the liner in place.

Inner Liner

Here is the liner setting inside the can:

It's not a perfect circle, but who cares? that doesn't matter. The liner also sits a few inches below the rim of the can and will be lifted up level with the top so that a base can be formed.

Furnace Prep

Setting aside the finished lid I began preparing the furnace. Before I can mix up some more refractory I needed to make some sort of liner to form the inner chamber of the furnace and  locate and add the tuyere so that an air source can be attached. First step, come up with a liner. The book calls for making two wood disks and wrapping a piece of sheet metal around that, allowing the liner to be pulled out after adding the refractory. I decided to use a piece of cardboard tube that I would leave in place and burn out as I cured the liner. The 10 inch diameter of the cardboard tube was a bit large so I cut the tube and choked it down to a 9 inch diameter.

Curing The Lid

After getting the refractory into the lid it still needs to be cured. Gingery's book calls for a pattern of temperatures and time to be completed in an oven. The lid I built, with the handles as I built them, wouldn't even come close to fitting in my oven, plus my wife wouldn't have liked me doing that anyway, so I just built a fire in my fire pit and cure the lid slowly that way.

I started with a small fire and stood the lid on it's side along an edge of the fire pit. After a bit of steam had stopped coming from the first side I turned the lid around to expose the other side to the low heat and after that, I built the fire up and tried to put as much heat as I could into the lid. It seemed to work, notice the crack running from the bottom of the lid towards the center. It actually shows up well in the photo, it was actually a very small crack, which I filled in later with a bit of refractory that I thinned out a bit to get it into the crack better.

I finished the off by covering it with the coals and letting the lid cool slowly as the fire and coals burnt out.

The Lid

After mixing I just packed the refractory into the lid, doing my best to make sure I got the mix through all the wires and then troweled top and bottom to get both surfaces as smooth as possible.

Refractory Mix

Here is refractory that I mixed up to fill the lid. I used just enough water to allow it to clump together. I broke the clump apart looking for a clean break to check the mix.

Furnace Lid

To convert the 10 gallon can into a working furnace I needed to line it with a refractory mix to be able to withstand the heat required to melt the metal. There are very good, higher temperature resistant refractory mixes available (at a cost), but the Gingery furnace is intended for the lower temperature requirements of melting scrap aluminum and tin so I decided to stick to the book and line my furnace with the mix he describes in his book. It is very economical and easy to make. The recipe calls for a mix of 2 parts silica sand and 1 part fire clay, both of which are readily available and inexpensive. I have read about a few other recipes based on this basic mix, but I decided to stick to what Gingery calls for.
The mix is simple enough and I thoroughly mixed the two ingredients together dry before I began adding water. Once I started adding water, I added it slowly with a garden type sprinkle can to try to avoid separating the sand from the clay. The process of using the refractory requires a curing process so the first item I made was the lid for the furnace.
The lid was straight forward enough. I measured the circumference of the lid, added 2 inches to the resulting diameter and cut a piece of 2 inch wide sheet metal long enough to produce that circumference plus a few inches so that I could rivet it together, not a very critical measurement is needed. Then, needing a handle of some sort to be able to move the lid around I split from the book design. The book calls for drilling some holes around the perimeter of the lid and adding some wire framework to the inside of the lid to help add some structure to the refractory as the lid had no top or bottom structure of it's own. The handle made in the book calls for the handles to made of this wire. I had some 3/8 inc re-bar laying around so I made a rectangular handle and then added some wire for some additional structure as well as using it to hold a 3 inch diameter can in the center, which will form a vent hole in the lid. Here is what I came up with:

The can is close to the center but not perfect by any means and the wire I used was just some wire I had left over from another project, I was going to use .032 safety wire until I found this stuff which is a bit heavier. I think it was used to hang picture frames, etc.

Getting Started

Hi!

My name is Mike. I am a helicopter pilot currently, but many years ago I was a machinist/toolmaker. A while back I ran across an ad for Dave Gingery's series of books on building a machine shop from scratch and it sounded like fun so a few years ago I bought the books and I have finally gotten around to getting started. I work away from home and that can make it tough to keep momentum going on projects but as I have finally gotten going on building the furnace I am hopeful that I can keep it going. Living in Montana and with winter approaching I may not be able to get much metal cast for a few more months but there are PLENTY of things I can continue work on through the snowy winter.

In case you don't know about the Gingery Projects, it all starts with building a charcoal powered furnace that can reach temperatures capable of melting scrap aluminum and pot metal (tin) which can then be sand cast to make the parts that can be assembled into various machine tools. The books detail plans to build several bench top machine beginning with a lathe and using that tool to build other tools such as a mill, a shaper etc. all using old methods.

The above trash can will be used to build my furnace. The book calls for using a 5 gallon metal pail. I am using a 10 gallon trash can so that I can get a bit more capacity.

Over the next few days I will cover what I have done so far and then I will try to carry on and keep things updated as I continue my progress!