Spruing for Centrifugal Casting by Don Norris Copyright ©1999, Don Norris. All rights reserved. (Please respect the copyright)
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Before we discuss My Way of spruing, I need explain that I cast the same amount of silver in the same size flask every time I cast. I believe that consistency is important in casting. If you are consistent about every step of casting you can make small changes each time you cast to find the best way to do each step. I decided a long time ago to use a Smith "Handi Heat" torch, which is a torch that uses acetylene mixed with atmospheric air (just the air in the room) for silversmithing and silvercasting. I used this torch with a number 3 tip instead of an oxygen-acetylene torch because I was taught that the extra oxygen would oxidize the sterling silver. With this torch and tip I found that I could melt 3 to 3 1/2 ounces of silver easily in a short period of time if I preheated the crucible loaded with this amount of silver in the kiln.
I found that 2 1/2 inch x 3 1/2 flask could hold just enough wax patterns that I could cast with 3 to 3 1/2 ounces of silver, and still leave a good 1/2 to one ounce sprue button. I wanted this left over sprue button for many reasons that we will have to discuss some other time. I also found that this size of flask make it more economical as far as how much investment is used per cast piece and the time involved in investing each flask. I always invest 4 flasks at a time.
I also make all my own molds so that I can use a small tree of small items like these leaves For photo, click here.. I use a 2 1/2 inch rubber sprue base that I have filled the center up with injection wax. Then I cover the entire top of the sprue button with treeing wax (Rio Grande) or sticky wax. Then, I melt a small hole in the center and stick the first sprue wire in it. The sticky treeing wax will hold it just fine without further melting. For photo, click here. I check the first one to make sure that it is not too close to the top of the flask. I want to keep it about a 1/4 inch away from the top of the flask. I check it by placing a pencil on top of the flask and making sure the waxes are at least 1/8 inch under the pencil (The sprue base adds about 1/8 inch when flask is seated). For photo, click here. The next sprue wire goes on the side of the one in the middle as close as I can get it without touching the first one. For photo, click here. I keep adding wax patterns on one side until the I think that I am close to the side of the flask. It is then time to check the see if it will fit inside the flask. For photo, click here. It is easy to do this by placing the flask over the waxes and down over them so you can check the clearance. For photo, click here. I really do not care if the waxes touch the sides of the flask. I have never had this make any difference. Never had it break out and run along the sides of the flask as I have heard and read about! I just do not want it to be so tight that the side of the flask pushes the wax over into the other waxes.
If some of the waxes need to be repaired or "treed" together, I do it as I am spruing. For photo, click here. I place some more wax under the last group on this side. For photo, click here. With this side done (Photo), I do the same thing on the other side. For photo, click here. Once this first line of waxes is placed straight across the sprue button, I start filling in on one side of this line of waxes. For photo, click here. I keeping checking to make sure they all fit into the flask. For photo, click here. After I do this on both sides of the center waxes, I put smaller waxes all over the button under all the waxes. (Photo), (Photo) Then the spruing is done (Photo) and I put the flask on to the sprue base. For photo, click here.
It should be noted that when I did this one, I got 54 leaves into this one flask. Chad then sprued up three more flasks. He got over forty leaves in each flask. Then these flasks were cast For photo, click here. Chad holds two of the flasks that he sprued and cast centrifugally (Photo) (Photo) I tumbled these just to clearly show how they were sprued and cast. (Photo) (Photo) (Photo). These four photos show the four sides of the flask that I sprued and cast. (Photo) (Photo) (Photo) (Photo) This photo show all the leaves that were cast in this one flask, the sprue button and the sprue wires after they were cut apart. (Photo)
©Copyright Don Norris, 1999