Short video tutorial by Expert Village on how to cast jewelry using the centrifugal casting method. The artists shows how to create a cast ring. Its not very detailed, but explains the general concept.
Some explanations of the technique including pictures of my previous castings:
1. The jeweler uses a soldering iron to heat wax in the sprue base to attach the ring. These sprues represent channels that will allow the molten metal to reach your piece. When you’re spruing your piece, you want to keep in mind the direction the metal will flow, and make all of the spues thick enough to allow the molten metal to move freely. If you want to cast more than one piece in a flask, you can create a sort of tree, with one large sprue in the center, and many smaller sprues attached to it leading to your pieces. Always keep in mind that none of the wax sprues may touch the steel flask. Keep them at least a quarter inch away from the rim of the flask and about half an inch from the top. Otherwise the molten metal can break through the investment and ruin the casting. Also, after you’ve finished spruing, you can apply a anti-bubble liquid with a paintbrush and gently coat the wax. This is an added measure that will prevent bubbles from attaching to the wax.
2. He then mixes investment with water in a rubber bowl. Some like to measure the ratio very exactly, but personally I go by feeling because I’ve done it a few times. It should be slightly thicker than pancake batter and not too watery, but no too thick either because then it will harden too quickly. I use rubber gloves and stick my hand in the mixture to break up all the clumps and get at the powder on the bottom of the bowl. Then I mix it up with a spatula. You can also use an electronic mixer.
Investment is extremely bad for your lungs, so make sure to always wear a respirator when dealing with investment and always clean up carefully afterwards and remove all residue from countertops, etc.
3. Remove the bubbles from the mixture by placing it under the bell jar of the vacuum pump until the bubbles rise and fall again. After they fall, count about 30 seconds. Remove the bowl and pour the mixture into the flask. I always tip the flask because my waxes are usually delicate and pouring the mixture directly onto the wax could break them. So similarly to pouring beer, pour along the side of the flask while holding it at an angle. Place the flask under the bell jar again and let the vacuum pump run for another 30 seconds or so until most of the bubbles appear at the surface. If you do not have a vacuum pump and bell jar, you can pour the investment into the flask and then hit the side of the flask gently with a steel rod or something until the bubbles come to the surface. The reason you do not want bubbles is because they’ll stick to the wax and create air pockets that molten metal can later flow into. This can make clean up much more difficult.
4. Let the mixture harden for about 2 hours, remove the rubber base, and place the steel flask with investment into the kiln. It needs to be raised up somehow so the wax can run out. Notice how in the vid he places the flask at an angle? In my old kiln I had tiles that had recesses carved into them to let out the wax.
As was said in the video, weigh your wax before attaching it to the sprue base and calculate the amount of metal you’ll need per flask. Metal calculations depend on type of metal also, you’ll need to add about 20 grams extra for the button. I think for silver you multiply the wax weight by 12 and then add the 20 gram button.
Once your investment is starting to harden, scratch the weight of metal needed into the investment, so you dont forget. If I’m casting 6 flasks, I will write down the placement of each cast in the kiln (back-right, back-middle, etc) and the weight of metal for each flask on a piece of paper so i can easily figure out how much metal to prepare per flask.
5. Run the kiln cycle. If you have a digital kiln, you can simply program it to run the cycle, if yours is manual, you need to monitor it and adjust the temperature every few hours.
Here is the burnout cycle posted on Ganoksin:
300 Degrees F for 2 hours
700 Degrees F for 2 hours
1350 Degrees F for 4 hours
900 Degrees F for 1 hour (Centrifugal casting it can be up to 1100 degrees F for 1 hour)
Hold at 900 Degrees F or up to 1100 degrees F for centrifugal casting until all casting is complete (Note: Sometimes if one has some very fine details in the wax a hotter temperature up to 1100 degrees F can be used, but only when using the centrifugal casting process.)
6. Once you’ve reached casting temp (1000-1100F), wind up your centrifugal casting machine, prepare the scrap metal and place the crucible into position. Put on some welders gloves and, using steel casting tongs, remove your flask from the kiln. Once the tongs have grabbed the flask, turn it 90 degrees so it wont slip from the tongs. Then place it into the centrifuge, make adjustments. Light your torch and begin heating the metal. Apply some borax once the metal is molten, and use a casting rod to stir the metal around. Once you’re sure it’s completely molten, release the centrifuge and watch the metal spin into the mold. Once the centrifuge is done spinning, remove the flask again with the tongs, let it cool until the button is no longer red (button side up) and immediately dunk the flask into a bucket of cold water. Submerge the flask completely, not a bit at a time. This is for safety reasons because if any of the investment is above water, the quick cooling can cause it to spurt and it could get in your eyes, or just burn you because it is HOT.
7. Remove all of the investment from the flask and metal mold, using a steel pick and a brass brush. Once the flask is clean, dry it to prevent rust. Place the clean casting into pickle to remove oxidation. Once it is clean, begin sawing off sprues and cleaning the piece up. 
metalsaddict 