Sand Casting

Sand casting is a good option, if you already have a part. And you can draw a parting line on the part so that the both halves can be pulled from the sand without distorting the sand. 

Lots of people use green sand, but I almost everyone prefers Petro-Bond sand so I choose to skip green sand and go straight to Petro-Bond. The only problem with Petro-Bond is the price.  With green sand I could have picked up the sand out of the Arkansas river that winds through Tulsa, Oklahoma and then added in some fire clay but instead I bit the bullet and paid $100 for 100 pounds pre mixed Petro-Bond. The price included shipping from a near by supplier. If you order Petro-Bond, note that you want the pre mix and not Petro-Bond II which is just the additive that is added to the sand.  Mixing it by hand is also not recommended because it really requires a muller mixer to do right. If you want to go with green sand, there are good detailed instructions at www.backyardmetalcasting.com.

Casting Flask

(1) Start by building some casting flask that will hold the sand. Casting is far to macho to just call them sand boxes.  Each flask has 4 parts.  My top or "molding board" and the "bottom board" are 1/2 inch plywood.  I added runners to the plywood to stiffen them and make the easy to pickup.  The frames are pine secured by 2 screws at each corner.  Nearly any board would work.  You can use brackets to strengthen the corners if needed.  The inside surface should be rough so the sand will stick to it, or you can add a thin strip of wood or cut a shallow groove to help hold the sand in place.  You must be able to accurately align a  pair of frame together after that have been taken apart, so I added a few dowel rods to each flask for this purpose. Others use interlocking blocks on the outside of the frames.  A pair of old door hinges would work well too, and would have the added advantage of allowing you to insert the pin and lock the frames together.   Locking the frames together is optional but it will prevent the molten metal from ever lifting the top frame.  The only thing to keep in mind here is that one of the frames in a pair must not have anything that would prevent the the bottom molding or bottom board from resting flush against the frames top or bottom.  Notice that the dowels on my frames are all fixed to one side and the latches I used can fold back so the do not extend above the edge of the frame.

Steps for Sand Casting

(1) Place your part/s on the molding board. Sprinkle them with parting dust. Simple Backing Soda works well as  parting dust and it's cheap.  I skipped the parting dust because it is only need if your parts have lots of detail. (2) Place a frame, called the "drag" around the part/s, then start adding your sand, being sure to tamp it in well around the parts, especially when there are fine details.   (3) Once the "drag" is full, level the sand with the top of the frame using the other board or "bottom board" that will also be used to cover the drag. Then hold onto both boards and turn the flask over so the "bottom board" really is on the bottom. (4) Remove the molding board.       (5) Use a knife or blade to excavate the sand around the part/s just until you can safely lift the part from the sand without disturbing the remaining sand.  This will be your "parting line".   (6) Add a "sprue" or the hole through which your molten metal will be poured.  I am using a pipe to mold the sprue.  First pushing one end into the sand to remove a core and form a hole that is a little deeper that the bottom of the part/s.  Then add parting dust. (7) Place the pipe back in place to from the sprue.  Paper towel rollers work well if you don't have a piece of pipe.  Then set on the top frame or the "cope".  Latch the frame in place if you have latches.   (8) Add more sand and again gently tamp it in around the part as well as the pipe to from the sprue.  There are special tools for this, almost anything including your fingers works well. A blunt 5 pound bock of steel make a good ram for packing frames.  Larger frame will need to be more tightly packed. (9) Flatten off the sand level the the top edge of the frame or "cope" and also form a funnel cup around the pipe that is forming the sprue.  This will give you a bit larger target when you pour the molten metal.  Be sure to leave some sand  between the funnel opening and the wood frame. (10) Gently remove the pipe that was forming the sprue. Then place the "molding board" on top.   (11) Unlatch the frames and carefully lift off the top frame or "cope" and set it on its side.  You should be able to rest it on its top, but less movement is better.   (12) Using a couple of knife blades, delicately lift the part/s from the bottom frame or "drag".  Be careful to lift the part/s straight up so as not the disturb the sand. (13) Using a knife or blade carve out the "gating" system that will allow the metal to flow into the part and the air to flow out. The "gates" connect the sprue to the part a little above the bottom of the sprue.  The vents are very small channels that run from the smallest section of the part to the edge for cope.  Blow out any loose sand and repair small imperfections. The carefully put the two halves back to together. (14) Time to melt some aluminum. This is my flower pot furnace, the details are above. Wait until the melt begins to glow orange.  Thermometers are not necessary.  Too cold and the pour will choke.  Too hot and there will be small bubbles.  After a couple of mistakes you will know when it's perfect.   (15) Pour the flask with molten aluminum.  Don't pour too slowly or the aluminum will harden too quickly in the gate, coking the part off.   (16) After 5 minutes the flask can be opened for inspection.   (17) Final Parts next to original after the being brushed off.   (18) The Petro-Bond that was not in direct contact with the part can be returned to the storage bin.  The rest can be sifted through a screen or "riddled".

Sodium Silicate Sand Casting

Sodium Silicate is what most professional foundries use to make sand casting fast, easy, and more reliable.  If your interested in making parts than showing off your skills then Sodium Silicate is for you.