That said, On with the show. The following two scenes show how to make a good furnace for little more than some creative shovel time and utilizing some items in ways that Underwriters Laboratories never thought of.
The Blower is something that I had sitting on a shelf. I made a plate to regulate the air flow through it, essentially a choke. You can use a hair dryer though I would recommend disabling the heating coils if you do. The pipe into the pit is actually a piece of tail pipe that rusted off my truck a couple of months ago. Only one spot had rusted through and I saw immediately the value of having a section of 2" pipe 'on hand' ; though at the time, not a clue what its future was.
Not pictured is my other blower That one I made from an old 18V saw, some plywood, and a section of 1 1/2" pipe. I power it from the truck when in use. It works but not nearly as efficiently as the above set up. One aspect of this that surprised me the first time I did it was the steam. Steam was popping out of the ground in places quite distant from the actual fire. I am quite certain that the moles or some other underground critter was quite peeved about my flamboyant use of coal and charcoal and none to happy about the way I was warming their little world.
Its hard to see within the flames shooting out of the pit: there is a 1qt cast iron Dutch oven in that pit. Its loaded to the brim with cans and broken cast aluminum, then lidded to retain the heat that is building inside. The lid also acts as a barrier to the atmosphere. There is paint and what not in side with the aluminum, the heat and what air is in there combine to burn that off and help remove any other oxidation that has taken place on the aluminum. This will be skimmed off once I am at heat and just before I pour.(the technical term is Dross.)Well, now we are melting metal. What is a body to do with hot metal. The following is a 'flask' that I made up. This one has never been used but is essentially the same as the others I have. (this one was in the process of drying out before I put it to use and was convenient to snap of pic of.)
These are really simple to build, cheap in materials. I use 4" Chase board since its ribbed on one side. This helps hold the sand in when flipping the Drag over to set up the Cope. Sand is critical. The finer it is, the better your finished product surface. There are ways of making your sand up without purchasing casting sand pre-made. I have been using the Petrobond product the last couple of melts but I have been doing this enough that it was worth the purchase. You can utilize sand, ground up cat litter(the cheap clay type), wood flour(from a power sander) and a small amount of NON-DETERGENT 30W oil. The whole mess should feel like combination of wet sand and clay, should hold shape easily and when broken apart, not crumble up. I prefer the oil over a water based sand due to control. It doesn't evaporate like water, won't build explosive pressures in the mold like water can, may smell like hell when burning but doesn't smell like wet socks when in storage, and seems to make a cleaner cast than the water.(that last is an opinion only, use your own judgment if you choose to use water)
The next pic is the casting I made from the melt above. The wooden blanks are shown with it. The trick with these is a beveled edge of roughly 1-2 degrees from 90. This allows you to remove the blank from the packed sand easier. The smoother your finish here, the easier your draw, and the less work you have to finish your end product.
The next pic is of the same parts but now separated from the sprue's. The parts circled in yellow are the sprues. One is the feed sprue, the other is an overflow to allow the thicker piece some reserve to draw from during cooling to minimize shrinkage. If you look closely in the red circle, you will see some flashing on the edges of the final product. This is normal in some circumstances. In this case, my flask was not clamped and the weight of the sand was not enough to hold the edges tight. Every pour will teach you something about what to, and what not to do.
Onward we go. When ever you are working with something that needs to be accurate; in this case, a gauge for drilling specific patterns in the arms of the press, you need a test surface. Underneath the piece in blue is my test surface. This consists of an old plate from a table saw that was on the curb, a piece of plate glass and bondo. The bondo holds the glass to the plate and I use more thirty weight oil to hold the 400grit paper to the glass. The 'machinist blue' in this case is a blue sharpie with a wide tip. It works great, is cheaper than machinist blue, and is much easier to find.
First pass: Nearly perfect. I am only concerned with this side since I will bring the others to true with the mill. Using a good milling vise, a set of parallels and 1/2" 4 flute end mill, I will have every surface within .001". BUT I need a perfectly flat surface to start. That's what the test surface is for.
As you can see, even with a great cast, not every surface is perfect. This one is only a couple hundreds off, but off is off no matter how close in most cases.
And here is my mill in action. I know, not everyone has a mill. With patience, a good test surface, scraper, blue, patience, some sweat, patience and more blue; anyone can get within a couple of thousands to perfect. Did I mention the patience part?
The Gingery series of making a machine shop covers this application. Here's a hint: How do you think they set the beds and ways of High Tech Lathes and mills back in Henry Ford's days? Think about it.
I promised no politics today and I will stand by that. Tomorrow though, well, Thats next year. See ya all in 2011! Stay safe and if in doubt, call a cab. Please.
