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The Aluminum Melting Forge and Crucible

For the forge I started with a small steel barrel that I found on the side of the road, its diameter is 18 inches. I cut it to a height of 2 feet, starting from the “floor” of the barrel. I also cut an 8″ ring from the barrel to be used later, as a lid. The forge barrel must be lined to hold and refract heat. Ideally you may find refractory cement in your area, but for me I was left with regular old concrete as my only choice. I used “Quikcrete”. One 80 lb bag will do, you will also need a cardboard round concrete pre-form with an 8″ diameter, lastly you will need several lengths of re-bar. The forge must have an air intake to heat the charcoal to the temperatures required to melt aluminum. I used a length of 2″ galvanized pipe as my air supply. I cut it to a 2 foot length, this long of a piece sticking out the side of the forge barrel allows the end to stay relatively cool so your blower will not melt. Blowers will be covered later. Bore a 2″ hole into the barrel roughly 2″ from the bottom, cut a matching hole in your cardboard pre-form 1″ from the bottom. You are ready to mix some concrete. I use a bucket or wheelbarrow. The concrete needs to be fairly viscous to prevent air pockets that will cause trouble when heating. First cover the bottom of the forge barrel to a depth of 1″ in concrete forming a liner floor. Take your cardboard pre-form and at one end seal it in duct tape, you don’t want any concrete getting on the inside of the pre-form. Set the sealed end of the pre-form on top of the cement layer in the bottom of the barrel, center it, and then run you air intake pipe through the side of the barrel and into the pre-form. The air pipe just barely needs to go into the cardboard, now center everything and fill the barrel with concrete around the pre-form. When filled, smooth out the cement to make it flush with the barrel top.

Next, take the 8″ barrel ring you cut earlier and lay it flat on a piece of plywood. This too will need a pre-form but one that is smaller than the 8″ diameter used earlier. The smaller diameter of the lid allows heat to refract towards the crucible but allows you an opening in the top to manipulate the crucible, feed metal into it, and to add fuel to the forge. For this pre-form I used an empty Country Crock margerine plastic container anything similar will work, but make sure it is not metal, once the concrete has hardened the plastic pre-form can be easily broken or melted out. Set the pre-form in the middle of the barrel ring and pour your concrete around it. I made two handles for the lid from re-bar and set them into the cement. Allow the concrete a full week to dry.

Making a crucible is not difficult, a simple steel crucible will do nicely for melting aluminum and copper. I started with a 3″ diameter pipe nipple that was 8″ high. My first crucible had a welded on steel bottom, but what is much easier, is to buy the steel cap for the nipple and simply screw it tightly into place. Near the open top of the pipe, drill two holes, one in each side, a 3/16″ drill bit is ideal. I then took a wire paint bucket handle, cut it down a bit and ran one side into each hole, then bent the wire to stay in place. This crucible handle is how you will manipulate it when it is orange hot. The crucible also needs a manipulation point on the bottom for the pouring of the molten metal. I welded on a steel half ring, but if you do not have a welder one can be made from the same material as the top handle. Wrap the wire around the bottom of the crucible and twist it on tightly with a pair of pliers, leave enough wire to twist a loop on the end.

These manipulation points, as I call them, are the backyard hobbyists way of completing the process inexpensively. If you watch a youtube video you will see that the “Professional” metal caster has a fancy set of crucible holders to take the crucible out of the fire and for the molten metal pour. These holders require two people for the pour and are fairly complex in design. I considered making a set but the forge work and materials just did not warrant such an investment in time. My method works just fine, the only drawback is that the paint bucket handle wire needs to be replaced every three to four melts. After several exposures to high heat, the wire becomes brittle, and can break when lifting the crucible out of the forge. I will cover cautions and dangers during the process in detail later on. To use the “manipulation points” all you need are two hooks with handles. I made mine with 2-½ foot lengths of re-bar, bend one end of each piece of re-bar into a hook. I drilled a hole in the other end of the re-bar pieces, I then used lengths of 1″ wooden dowels for the handles. Since the handle end of your hooks will remain cool nearly anything can be used, but what you want is a T-shaped handle for the hooks. Now for a test, place your crucible on the ground, with a one homemade hook in each hand. Pick up the crucible by its top handle, I am right handed so I use my left hook, no pun intended, to raise the crucible. Now take your other hook and put the end through the crucibles lower loop. You will use the lower manipulation loop to raise the crucible bottom for the pour. Practice pouring and work out any kinks in the system. (When it is orange hot and filled with 10+ pounds of molten aluminum it will be too late to work out kinks!) I have used my steel pipe nipple crucible for over 30 melts and it shows no signs of metal fatigue the same holds true for the homemade forge.

Castings Tools

We are getting close to drawing a mold and putting fire to that new forge, but you need to make some casting tools first. It is very helpful to have a casting table, nothing fancy, just a small table with some 2 X 4 walls to keep the sand on the table. The table walls also give you a place to rest your molding backboard on, the backboard is where you will rest your cope or drag, giving them a temporary bottom for sand filling. You will need 2 backboards. I cut mine from 3/8″ plywood, they need to be just wide enough so the guides on your cope and drag will hang off the sides of the plywood while still providing a complete bottom for the flask. Another critical tool is a riddle or sifter, you can not cast without one. The riddle can be made from 1/4″ mesh screening. 1/8″ mesh is just too small and difficult to use and anything bigger than 1/4″ mesh allows large chunks of casting sand to get through, which ruins the detail of the casting. I cut the mesh screening into a piece 12 x 18″ Then made a matching square using lengths of a 2 x 4, I tacked the screening to the 2 x 4 using 1″ nails, I nailed them in about halfway then bent the rest of the nail over the screening. The riddle needs to be fairly tough, it needs to hold the weight of the sand and the downward pressure of pushing the wet sand through the mesh into the cope and drag. Next is the “Rammer”, this is used to push the casting sand down over the parts to be replicated, after it has gone through the riddle, and compact it in the cope and drag. The end needs to be square for compacting at the corners. A 4″ piece off a 2 x 4 serves this purpose, next attach your square to a vertical length of a dowel or broom handle with a wood screw. It is helpful to paint the rammer so it will not absorb moisture.

Once you have drawn and separated any mold errors and small faults will need to be corrected, you will also have to cut channels for the molten metal to run through. A good start to your sand detailing tools can be had at hobby lobby with a set of clay molding tools for around $7, however if you don’t want to spend the money, then they can be made. The tool I use most in sand detailing and trough cutting is a simple soup spoon that has been bent into a U shape with a pair of pliers. Be sure to check with your Wife first before raiding the kitchen drawers for silverware to ruin, I learned this the hard way! A dull X-Acto knife is also useful for fine detail cutting. You will need two lengths of metal or PVC pipe varying in diameter from 1″ to 1 ½”, these will be used for cutting entry and exit channels for the aluminum. They do not need to be long pieces 6 to 8 inches will do. You will need a vent wire, this simple tool can mean the difference between success and failure. Take a metal wire hanger and snip out a straight length about 8″ long. Twist one end into a loop for grasping and hanging when not in use, and sharpen the point at the other end. You will also need a “rapper” this is a metal fork similar in design to a tuning fork. The rapper is used to gently free parts to be replicated from your sand without destroying the mold when you remove them. Mine is simply two bolts driven into the end of a dowel to form a Y shape. I will cover this in more details when we get to drawing the mold. One other piece of equipment needed in this process is a simple propane torch, any Wal-mart special will do. Lastly a stiff straight edge roughly 12″ long will be needed to smooth the mold bottom and top. I used an old baseboard, but nearly anything will work. The primary tool used in sand casting will be your bare hands!

There are still a couple of fire tools to be made, The most important is the skimmer. The skimmer is used to rake out bits of charcoal and other impurities that float to the surface of the molten aluminum. The skimmer is also used to test the metal to see if it fully molten and to aid in feeding metal into the melt. Once again you will need a dowel or wooden broom handle around 2 feet long. I then went to hunt down a long threaded bolt, I came up with a 1/4″ fully threaded bolt 16″ long. Next you need a good sized washer, this will do the actual skimming, I found one with an 1 ½” diameter. I slid the washer down the bolt until it came to rest on the bolts end, then locked the washer down with a 1/4″ nut, making sure it was good and tight. Then I drilled a slightly smaller vertical hole into the dowel, if you are careful you can get the top end of the bolt to “bite” into the wood. I screwed it in about 2 inches, then for good measure attached a hose clamp around the end of the dowel to further secure my bolt/washer apparatus. You now have a skimmer. The next fire tool is a pair of metal tongs, kitchen tongs can be used, I use these to feed oddly shaped pieces of aluminum into the melt. While your cement is drying it is time to secure an air supply for the forge. This can be done old school or new school. I first tried it with a homemade box bellows, this worked but was very slow and took serious elbow grease. I was very sore the next day when I decided to use an electric air supply. We may not always have electricity and I keep the box bellows stored away for a rainy day. I came up with an old hair dryer at the local thrift store for under a $1, the older hair blowers last many times longer than any of the newer ones. Start with the used hair dryer, if you really take to sand casting then move up to a leaf blower. I attached my air supply to the air intake pipe using a PVC fitting, even duct tape will work, the extra length of the intake pipe gives you many options.

Note: The next installment of this article series will describe supplying fuel for the forge.

Jim,
I couldn’t agree with Dan more, sand casting takes some experimentation and tinkering. Once you get your sand and flasks working, it’s a snap, but you will mess up a lot of casts before you get everything tuned. His tip for using cat litter as bentonite clay is pure genius, but be prepared to test several brands before you hit on one that works for you. Clay cat litter can be made from almost any clay. Sodium Bentonite (or western bentonite) is often chosen for it’s absorbency, but any given brand of kitty litter may vary between lots. “Bentonite Clay” can be either sodium bentonite, or calcium bentonite. They both work for green sand, but they have distinctly different qualities. Other clays can also work well for lead, pewter, or even aluminum casting, but won’t hold up to high temperatures very well. Wal-Mart used to have a cheap store brand cat litter labeled “bentonite clay” that I believe was almost 100% sodium bentonite: ‘Special Kitty’, sold for a few dollars in a 25 pound bag. It works very well for aluminum, copper, bronze and brass. I believe it would hold up with cast iron, but I haven’t tried it yet.

Before you start making your own green sand, It might be worthwhile to check around in nearby cities and look for a commercial foundry. (They are pretty rare, but a lot of cites still have one). A lot of founders are friendly and eager to help a beginner get started. A lot of them will sell you used green sand for very little if you will haul it away. They may also sell you “southern” (calcium bentonite) or “western” (sodium bentonite) bentonite clay or fireclay (used to make your furnace), cheaper than you can find them on line. They may also have a wealth of good advice. As a beginner, it’s really nice to get a look at a working foundry and see what “right” should look like. Check out their safety precautions while you are at it.

Be careful of breathing dust and fumes from your foundry. Melting metal puts out some nasty chemicals and mixing sands can raise clouds of dust. Great article! V/R, – JIR

I set out to learn how to sand cast aluminum and set up a metal working shop at my home more than two years ago. Let me start by saying that sand casting can not be learned overnight and although books are helpful, especially the David Gingery Book 1 “The Charcoal Foundry”, there is no substitute for hands on experience. You have to get out there and try, try, try. To get started in aluminum casting it is critical to first come up with the casting sand. This was really difficult where I live, the sand must be very fine to gain the detail for the part being cast. And equally critical is adding the right amount of bentonite clay to hold the sand together. I wanted to come up with materials locally so that I would have a continuing supply. My journey started by the river where erosion had broken down the limestone to a workable fine grain sand. I shoveled about a hundred pounds and brought it home. After many hours of sifting I believed I was ready to go on to the next step. Again I walked near the river and searched out local reddish clay. Again I brought it home and ever so slowly got it sifted and cleaned up. For the first test batch, keep in mind that I was nowhere near even lighting a fire at this point, I mixed 7 cups of sand to 3 cups of clay. Then I added around 1 cup of water. I let the sand “Temper” overnight and the next day started pressing some metal parts into it to see if it would hold its shape. It was a failure, the casting sand would not stay together my clay was no good. I started looking for actual bentonite clay, there are no deposits within 200 miles of where I live, and then I discovered that plain cat litter is 100% bentonite clay.

Having cats I already had litter on hand, but the pieces were far to large to use, and I had to come up with a way of breaking it down. This was another adventure, I tried water, vinegar and a mortar and pestle to no avail. I had nearly given up when I decided to throw a few cups into my “Brass Shaker” or cartridge case tumbler. After 10 hours the cat litter was broken down enough to add to my sand, I still had to sift out the larger pieces. I mixed 7 cups of sand to 3 cups of bentonite clay. The ratio remains the same whether you are using cups or any other unit of volume. I added 1 ½ cup of water, mixed, and let it “temper” overnight. Sure enough this worked the sand held its shape but was still porous enough to let trapped gasses and steam out. I even experimented with molten lead on some simple open face castings. The coolest thing about sand casting is that all required tools and even the forge and forge fuel can be made at home costing very little money.

The Casting Flask

The casting flask is a two part box that is open at the top and bottom for compacting sand around the item you wish to replicate. It consists of a “Cope” top part and a “Drag” the bottom portion. Making your own casting flask is not hard I started with a 2 X 4 and cut it into 12″ segments to make a total of 8 parts. 2 X 4’s placed on top of each other give your flask a total depth of 7″. This is a good starting point for replicating smaller parts. I am a huge sci-fi fan and my goal with the first castings was to make a “Lightsaber” or more precisely a “Lightsaber” pommel. If you wish to make larger parts you will need a larger flask, but it is important to START SMALL, there is still much to learn. You will also need some smaller board such as a segment of 1/4″ plywood to make the guides or line up points. It is imperative that the Cope and Drag line up together each time you put them together, and that the two parts are as flush with each other as possible. Take four of your 12″ segments and form your first square on a flat surface such as a table or board. When you are satisfied that your square is flush clamp it together tightly.
I found out the hard way that when you drive in the wood screws it can throw the whole thing off, if not clamped. I used a Work Mate bench as my clamp, you can use nails as well but the banging can quickly throw the boards out of alignment. A total of 8, 3 ½” wood screws, two at each corner, and I had the first half of the flask. Now form up the second half of the flask but instead of using a table, place your four segments atop your newly completed drag. This ensures a good fit, clamp it, then run in your wood screws. You now have a cope. It is time to make your alignment guides, start by cutting two triangle shapes from a 1/4″ piece of plywood or whatever you have laying around. The triangles need to be roughly 6 X 6 X 6, the triangles will be attached to your cope. Again clamp your cope and drag together making sure the two halves are as perfectly aligned as you can get them. It took me two wood clamps and the work mate to lock things down. Take your first triangle and put it halfway between the cope and the drag, making sure half the triangle is facing point down towards the bottom of the drag. Nail it in place, the nails will only go into the cope, not the drag, I used small 1″ nails.

Next, cut two small 1 X 5″ strips from your plywood and place them tightly against the triangle point on the drag only. Nail them in place, what you are doing is ensuring that the two halves of your flask fit together at the same point whenever they are separated. Repeat the process on the opposite side of the flask. Next you need to add handles to both parts, when the cope and drag are “rammed up”, or filled with compacted wet sand, they can be quite heavy. You will be moving them around often when you are making the mold or “drawing the mold”. I used some scrap 1 X 1″ boards cut into 4″ lengths and nailed them to the sides opposite the guides. Lastly, you need to give the entire inside of the flask a heavy coat of lacquer. Clear spray paint or plain paint will work also. The casting sand will be wet when used and you don’t want the moisture creeping into your boards. You now have a Casting Flask, these cost $70 to $300 if ordered off eBay or other vendors. There are other types of casting flasks but this type will be used for most home castings. Next up, the forge and crucible.