The Home Foundry, Metal Casting – Part 3, by Dan in Oklahoma

Forge Fuel & Homemade Charcoal

The aluminum melting forge is fueled by hardwood charcoal. To begin making charcoal you are going to need 2 steel barrels. One standard size 55 gallon drum will serve as your outer barrel, the second barrel is a little more difficult to acquire. The inner barrel or actual charcoal out gassing barrel needs to be small enough to fit inside the 55 gallon barrel. The smaller barrel also must have a lid that can be locked in place during the cooking and removed later to extract the charcoal. I was fortunate enough to find Military food barrels at a local surplus store. These are 25 gallons, they come with a lid and locking ring. If you are fortunate enough to find some of these buy as many as you can, they are highly useful. I keep all of our dried goods in them, they are great for storing and mulling your casting sand, and ideal to make charcoal. Drill or knock roughly 8 holes in the barrel lid, the holes do not need to be more than ½” in diameter. These holes will allow your hardwood to out-gas.

Next, you need to come up with some hardwood pieces. Split firewood logs work you just need to make sure the pieces are small enough to fit into the forge. Most woods make good charcoal especially pine, construction sites will often allow you to haul away their cut-off scrap , but you cannot use plywood, since it is highly toxic when burned. The same goes for any type of [resin-impregnated] particle boards.

Fill your smaller barrel up with hardwood, go all the way to the top, just make sure there is enough room to put the holed lid on and lock it. Now place the smaller barrel(Holes Up) into the larger 55 gallon drum. There is another method where the holes are places down and gasses coming off the hardwood can fuel the fire, I have never had any luck with this method. For the charcoal making burn in the 55 gallon drum, tree trimmings work quite well. It takes some time for the fire to get hot enough to burn away the volatile gasses from the hardwood leaving you with charcoal. You will need to keep feeding the fire and watch the holes in the charcoal barrel. When the correct temperature is reached flames will shoot out of the holes of your charcoal barrel, this is the out gassing. After the volatile gasses have burned off I add one more round of fuel to the fire and let it burn out. Usually I let the whole thing cool overnight, it is not worth the trouble to get in a hurry and haul a hot heavy barrel out of another hot barrel. The next day, take your 25 gallon barrel out, pop the lid and have a look. You should have nice black charcoal pieces ready for the forge. This is enough charcoal for one melt, it will ignite easily and burn clean and hot. The pine charcoal is also great for use in your steel forge, and will cook an excellent steak as well. There are many other methods available to make your own charcoal but this method works and is fairly inexpensive and does not take up too much space in your yard.

If you have the funds and do not want to go through the process of making your own charcoal, then it can be purchased. There is a brand of hardwood chunk charcoal for around $8 for 20 pounds, it works well in the forge, you can also use the cheaper dollar store briquettes. The little square charcoal briquettes have some big drawbacks, they are hard to ignite and even worse they are extremely messy when used as forge fuel. The air flow causes them to spit small chunks off while burning, and these little cinders go everywhere, they can cause fires, burn you and fill up your crucible with trash while melting. I would only use the briquettes as a last resort. You have fuel, you have a forge and crucible, you have sand, flask and tools, it is time to draw your first mold.

Drawing the Mold

There is an art to drawing your mold that can only be learned by doing. It took me two years to get this process down and I still consider myself a novice. I need to mention again that you have to keep pushing forward and try, try, try If your mold goes wrong and falls apart, keep trying If your mold goes right and your pour gets ruined wasting hours of work, keep trying Nothing in life, that is worth doing, is ever easy. You will get discouraged, you will have failures, but don’t give up. I am going to talk you through a split pattern mold. This is the easiest one to do, I recommend that you draw many molds before even lighting a fire, I wish that I had.

You are going to need some parting powder, parting powder or dust is sprinkled liberally over the parts to be replicated and at the seams of your cope and drag. The parting dust provides a barrier that allows parts to be removed and seams to be separated without adhesion to the surrounding casting sand keeping your two part mold intact. I use diatomaceous earth as my parting dust but I started with common baby powder. I drew many a mold with baby powder before learning that the baby powder absorbs moisture while diatomaceous earth does not. The difference between the two, in my opinion, are hardly noticeable. For a parting dust spreader simply put some dust into an old foot sock, hold the sock end closed and shake vigorously over your parts to build up a layer.

You are going to need a pattern, this is the object you wish to make a negative of in casting sand so a positive can be made in aluminum. For these beginning molds keep it simple don’t try to make a candelabra for your first mold, or in retrospect, a light saber. Lets say that you want to make an aluminum sphere 6 in diameter and you already have that sphere but it is just a wood ball at this point. For the split pattern mold start by cutting your wooden sphere in half . You now have two half spheres that need some alignment points, so the two halves fit together exactly the same way each time you separate them. Two small 1 nails with the flat end cut off will serve this purpose. Drive both nails ½ deep into one sphere half, match each up in the opposite sphere half and drill a ½ deep hole using a drill bit with a slightly larger diameter than the nail. The two sphere halves can now be joined together using the nails. Make sure that the fit is not tight as you will want them to separate easily in the mold. Now that you have a pattern it is time to start using all that homemade equipment. I trust that you have added water to temper your sand? This should be done, ideally, the night before drawing your mold, but the sand can be tempered in just one hour if you forgot. I keep my sand in one of the lidded barrels mentioned earlier, so it is always tempered and ready to go. Contrary to what many have written do not be overly concerned about adding too much water to your sand, I will cover a drying process a little later on. Grab a handful of your sand and squeeze it together in your fist. It should be wet to the touch but not slimy or runny. When you open your hand you should have a nice fist shaped ball in your palm. Grab the fist shaped ball in both hands and break it, it should offer some resistance and the break should be clean. If it is overly crumbly you need to add more water and possibly some more bentonite. You will know with a bit of practice.

Rest one of your backboards between the 2x4s on your casting table then grab your cope. Place the cope triangle points facing down and resting off each side of the backboard. You need a flush fit between the cope and the backboard with no gaps. Take the sphere half with no nails in it and place it(flat side down, concave side up) on the backboard centered roughly in the middle of the cope. Take your sock of parting dust and shake it vigorously over the cope and the sphere half pattern. You want a good covering of parting dust over the backboard (floor) and over the pattern, if it looks thick to you, don’t worry about it, the casting sand itself will compact the parting dust layer. Being careful not to shake the pattern lay your riddle on top of the cope, you should have sand at the ready on your casting table. Grab a handful of sand and place it in the riddle, gently at first, begin pushing the sand through the wire mesh. You can use a plastic paint scraper for this if you like, but I just push it through with my fingers. Keep going until you have a good layer of sand over the entire cope bottom and pattern, the sifted sand should come up to the bottom of your wire mesh. Pick up your riddle and set it aside, then gently push the sand down with your hands, compacting it around the pattern and cope floor. Put your riddle back onto the cope and push through another layer of sand but this time make sure the sifted sand covers the corners and sides of the cope. Again put aside your cope and compact the sand with your hands. The first and second layer of sand over the pattern are the most important, this is the sand that the aluminum will make contact with. Compact it carefully at the cope edges and corners, you have now effectively locked the pattern down in sand.

Riddle another layer of sand into the cope and this time when you compact it with your hands you can push down harder making sure that you are capturing all the detail of the pattern. Compact the sand on the pattern and the pattern sides, you want to make sure there are no voids or empty spots which can misshape the casting. One last layer of riddled, hand compacted sand, should be enough for a simple casting. Now you can just grab handfuls of sand and fill the cope, it is now that you will use the rammer. For each layer of sand put in, you need to compact its entire surface area with the rammer, paying close attention to getting the sand at the corners good and tight. Start ramming at the edges first, it is OK now to push down hard, and work your way into the middle of the cope, with the rammer. Keep doing this until the cope is full and the compacted sand is an inch higher than the 2 X 4 walls. Take your stiff straight edge and using the 2 X 4’s as your guide scrape or cut off the sand. You want the sand flush with the 2 X 4’s. Now take your other backboard and rest it the same way as the first on your casting table. Gently pick up the filled cope, flip it over and rest it (Pattern Up) on the second back board. Do not worry, the compacted sand has formed a friction hold with the wood of the cope and will not fall out. With a larger flask you need to add some sand holders but a small 12 X 12 flask holds just fine with friction.

Have a look at the first half of your mold, you will see only the sphere half bottom surrounded by whitened sand (Parting Dust). Clean off the edges of the wood only, if any particles have gotten onto the mold itself they can be blown right off with either a small bellows or your mouth. Try not to inhale any particles when you are readying yourself to blow. With the cope resting on the back board it is time to make the second half of the mold. First grab the other half of your pattern and mate it to the first sphere half using the nail guides. Next grab your drag and using the alignment triangles, which are now facing up, mate the drag to the cope. Make sure the 2 x 4’s of both the cope and drag are flush with each other with no particles between them. Sprinkle in a hearty layer of parting dust over the pattern and the drag (Floor) which is now sand and completed pattern instead of the backboard. Then exactly repeat the sand riddling and compacting process you just completed with the cope. Fill past the drag top and scrape off the excess with the straight edge just like before.

You are ready to separate the mold, making sure you have your second back board in place, grasp the handles of the drag and gently pull it apart. Sometimes you need to wiggle it a bit to get it to separate from its triangle guides. Once it has parted, flip the drag over (pattern up) and set it on the second backboard. The cope and drag should be lying next to each other and they should both contain a pattern half. This is why it is important to maintain a loose fit on your pattern guide nails. If half of your pattern does come out of the sand, DON’T PANIC, at this stage many errors can still be corrected. Continue the separation of the mold and get the cope and drag rested, then gently pull the pattern half that came loose off, making sure you don’t pull out the other half in the process, then simply place it all the way back into its mold. If it did come loose then most likely some of the sand at the edges in direct contact with the pattern came loose as well. This too can be fixed by pressing in some extra fresh sand, once the pattern is back in place, and smoothing it with your fingers. If it wants to crumble on you, dip your fingers into some water then smooth it.

It is very important that your pattern remain in the mold during the next step, which is sprue, riser and channel cutting. The sprue is the actual hole in which the molten metal will be introduced to the mold, on the opposite side of the sprue; I like to cut a riser, the riser is a hole smaller in diameter than the sprue, in which the molten metal can exit the mold after passing through and filling the pattern cavity. Many sand casters do not use a riser but having this second hole in the top of your mold has several advantages. It adds extra molten metal weight to the pattern cavity and it also tells you when the mold is holding all the molten aluminum it can handle. It is awful when you overfill a mold with aluminum, molten metal running off the sides, is dangerous, to say the least, and when it hits your 2 X 4’s it catches them on fire and emits a foul smoke. My casting flasks have many burns. Now there is a complex mathematical equation that explains how molten metal weight gets your pattern cavity filled, but to put it simply, the weight of the metal at the sprue and the riser will fill the pattern cavity nicely before it cools enough to solidify. Lastly you need to cut channels or gates from the sprue to the pattern, and from the pattern, to the riser. Think of them as small canals that allow metal to flow.

The sprue and riser will be cut into the cope or top part of the mold only. To accomplish this you will need your 1 and 1 ½” diameter segments of pipe that are roughly 6 to 8 inches in length. PVC pipe works but thin walled metal pipe works even better. With the pattern still facing up in your cope look where the most empty sand area is, you do not want the sprue to be too close to the pattern or the wooden cope wall, find an area that has at least 1 of sand between both the pattern and cope wall. This is why it is important to center your pattern in the flask. For this hypothetical pattern there is plenty of empty sand room all around. Pick a patch and run your 1 ½ diameter pipe vertically all the way through the cope sand until you strike the wood of the backboard. Then gently pull the pipe back out vertically, the cut sand will remain in the pipe, and you have just cut your sprue. Now repeat the process with the smaller diameter pipe on the opposite side of the pattern, the sand will remain in the pipe and you have added a riser to your mold. Be sure to remove the casting sand from your sprue and riser pipes with a long screwdriver, if it dries in the pipe, it is a pain to get out. Now you need to pattern out the location of the sprue and riser holes in the drag or bottom part of the mold so you can cut your channels. This patterning in the drag does not need to be 100% accurate so you have several options. 1. Put the cope and drag back together and run your pipes back through the holes to make an indentation in the drag sand. 2. Take a ruler and measure the location of the holes in the cope then use the measurements to find them in the drag. 3. Just guesstimate.

With your drag (pattern up) it is time to cut your channels and filter, this is where you will use your bent kitchen spoon. The channels and filter will be cut in the drag sand only. The filter is a trough or trench cut below the sprue (Larger Hole) its purpose is to catch any errant particles or trash that may get caught up in the molten metal pour as it runs down the sprue. The particles and trash collect in the bottom of this small trench and allow clean metal to run through the channel into the mold cavity. It sounds far more technical than it is, simply cut a small trench in the drag sand below the sprue. It is important that the filter trench be slightly lower than the channel. From your filter trench cut a straight U shaped channel all the way to the wood of the pattern, scoop away the excess sand and drop it into your casting table. Be sure to blow away any particles that may fall onto the mold. Smooth down the entire filter trench and channel with your fingers, any excess particles will be washed into the pattern cavity when you pour. The riser channel is a bit easier, there is no filter trench to worry about, just cut another U shaped channel from the riser to the pattern and smooth it down with your fingers.

Now we need to remove the two wooden sphere halves (pattern) from the mold. This is where your rapper comes into play, start with the pattern half that has the nails in it. Use the nails as your rapping points. Take your Y shaped rapper and gently strike the nail with the two rapping bolts using a side to side motion. I must emphasize gently here, you are not trying to knock out the pattern, you are trying to loosen the pattern from the surrounding casting sand. Rap both of the nails until you see the wooden pattern move just slightly in the sand. When you see the slight movement it means the pattern is free and can be lifted out. Grasp a nail in each hand and slooooowly wiggle or rock it out. If there is any damage along the edges don’t panic and follow the procedure detailed earlier in this segment. Now to rap out the wooden pattern half with no nails. To create a rapping point I use a small punch inserted into the holes drilled earlier. Once it has been rapped loose from the casting sand, two small punches, or something similar, will be used as the grasping points. Insert a tool into each hole, angle each tool to create a friction hold and wiggle it out. With the pattern removed you need to smooth down the channels cut earlier with your fingers, where they meet the pattern cavity, this will allow an unobstructed flow of molten metal into and out of the cavity.

We have one last cut to make in the sand, this is the funnel cut, and it will be performed on only the cope. Take your cope and rest it on its side, make sure it does not fall and ruin your work. You are going to make this cut from the top side of the cope. With the pattern cavity side facing away from you locate the sprue hole (Larger Hole). Take your dull X-Acto knife or even a butter knife and cut a funnel shape around the sprue hole. This greatly helps with the accuracy of the pour, channeling the molten aluminum directly into the sprue. Smooth the whole funnel cut down with your fingers. Be careful not to cut the funnel too deep, this can weaken or ruin the mold cavity on the other side. Before laying the cope back down you need to vent the cavity. This is an important step performed on the cope side only. When the molten aluminum hits the wet sand it creates steam, the vent holes in the cavity allow the steam to escape. Grab the vent wire you made earlier, rotate the cope so the pattern cavity is facing you. The venting only needs to done on the pattern cavity, nowhere else. Push the wire through the cavity until it pokes through on the other side where you just made your sprue funnel. Go gently and slowly with the vent wire both when pushing and pulling it back out. I believe in profuse venting, so on a 6 pattern cavity like the one described, I would vent it 20 times, make sure the vents are all over the cavity. When you are finished with the venting wire while the cope is still on its side, blow off any and all excess particles from both the top and bottom. If a particle is giving you trouble just wet your finger tip, or even a Q-Tip and gently touch the rogue particle, it will stick to the wet surface and can be removed.

Burning the mold is the last step, and once again it is an important step. Steam is our enemy and will ruin the casting. You need to get as much moisture as you can away from the points that will make contact with the molten aluminum. To accomplish this your friend the propane torch will be utilized. Ignite your torch and start burning, burn your sprue and riser from both sides, burn your channels and filter trench, and burn that cavity especially the drag (Bottom Side). You will see the moisture burn away from the sand when the blue flame is put to it, once the moisture has burned away, the sand becomes harder and more brittle, you must be very careful not to bang the cope or the drag. When the mold has been burned blow off any excess particles, it helps to turn the mold cavities upside down and hold them above your head and blow. Lastly you need to very, very carefully put your cope and drag together. You have just drawn a mold It is ready for the pour, a good rule to follow is never start a fire until you have fully drawn your mold. You can prepare the forge before drawing the mold but don’t ignite it.

I need to also note that you are under a bit of a time constraint after burning the mold. As soon as the torch is shut off, moisture begins to creep back into the burned spots. My own rule on this is to re-burn the mold if it has set for two hours. [JWR Adds: Or less, in very high-humidity climates!] As for making a mold one day and using it on the next day, forget it, it is a same day deal. There is also an internet rumor floating around that if your sand is too wet the mold can explode. I have poured into overly wet sand on several occasions, the casting was wrecked, but there was no explosion. The venting and burning of the mold will alleviate any steam problems making an explosion impossible. Aluminum has a melting point of 1,220 Degrees F, this is a relatively low melting temperature, which is why aluminum is such a good metal for the backyard caster. If you were to melt copper you would be dealing with a melting point of nearly 2,000 degrees F, with this much higher temperature an overly wet mold explosion is a real possibility. The next installment of this article will cover safety concerns, the melt and the pour. (So don’t start doing anything except mold-making until you have read the next installment!)