A jewelry centrifugal casting machine uses the weight of the metal and centrifugal force (even if only an apparent force) to fill the mold. A jewelry vacuum casting machine uses a vacuum to suck the molten metal into the mold.
Differences between centrifugal and vacuum casting will be explaining in the step-by-step guide below. Otherwise, these steps apply to either method.
1.Make or buy a wax model or pattern.
2.Check the model for any defects and repair if needed. The more finished the model, the less cleanup the finished casting will need. Model materials are easier to work on than metal.
3.Weigh and mark the rubber sprue bases.
4.Mount tree wax on the sprue base. Melt wax where the sprue wax and the sprue base meet. You can use an alcohol lamp and a large sewing needle stuck into the end of a wooden dowel.
5.Mount a small sprue onto the model, preferably in a spot that won’t be visible on the finished piece. Put a fillet of wax where the sprue is attached to the model.
6.Secure the sprued model to the tree. Keep the sprue for the model as short as possible. The sprued model can be attached with “sticky wax” or by using the hot needle again.
7.Assemble the flask and base and recheck your clearances. Models should be at least 3/8” from the flask wall. Allow for at least 1/2” for investment to cover the model.
8.Remove flask from base and weigh the sprued base. Subtract the weight of the sprue base and you have the weight of your models and sprues. To figure how much metal will be needed, you’ll have to do a little math.
9.Put the flask and sprued base back together. Check your clearances again. (For vacuum casting, cut soda straws 1/2” to 3/4” shorter than the height of the flask. Plug one end with wax and clip it to the side of the flask wall with a bobby pin and seal the end.
10.Instructions for mixing investment are included with the investment. In general, put water into the rubber mixing bowl. Then add the investment. Mix the investment to the consistency of pancake batter.
11.Vibrate the mixing bowl on a vibrating platform. (If you‘re using a vacuum machine, place the mixing bowl on the investment table. Put the bell jar over the bowl and turn on the vacuum. The investment will “boil” and turn frothy.
12.While tilting the flask, slowly pour the investment into the flask until it’s full. If you don’t have enough mixed investment to fill a flask completely, dump it out and mix more investment.
13.Vibrate the flask on a vibrating platform or vacuum the flask the same way as the mixing bowl. While vibrating the flasks, tap on the side with a metal rod or a screwdriver. This helps shake the bubbles loose.
14.Let the investment set up. Scratch an identity mark in the investment.
15.Remove the rubber sprue with a twisting motion.