I bought the metal spinning CD from James Riser and the two DVD set from Terry Tynan. But nowhere was it mentioned how to determine what size to make the starting disc. Or, if it was, I keep missing it. Anybody have any info on this? Thanks, Eric R Snow
As I understand the process, you would take a flexible tape measure from one lip of the shape to the other lip, going across the bottom. (You could do this off a drawing of the cross section as well). The shrinking occurs in the other axis (circumferential axis), but this dimension should not change much during the spinning process. Then add something to the diameter, maybe 1/2 inch, which will be cut off after the shape is completely spun. Ultimately you will tune this dimension through trial and error, after you have spun a piece or two using the form.
I admit that I am talking theoretically, but I have been working on forming sheet metal using other techniques for some time, and have a good understanding of what is happening when you stretch or shrink sheet metal.
Richard
Eric R Snow wrote:
Eric, first a thank you for buying the DVD. Asking what size to cut a circle for any given shape to be spun, is really an no more than an educated guess, it depends on the type of material to be used then the gauge, shape of the spinning, the spinning tool you will use to spin the part, etc the list goes on. A spinner will just take an educated guess from previous jobs he has worked on, spin the part down and if he finds it to be too small he will stretch the material to size as long as the tolerance allows, if it is too big he will simply trim off the extra material. If he removes an =BC" by trimming he will make the circle size =BC" smaller, or visa versa then cut all the blanks required to spin the job.
Hope this helps
Terry Tynan
Eric R Snow wrote:
It helps some. I did spin my first part using the proper too a couple days ago. Though small, it came out nice. I'll post pictures in the drop box later. ERS
I would be surprised if the disk would stretch that much. I would start with a little less than twice the height plus the base diameter. Gerry :-)} London, Canada
Gerald, I do hollowware in sterling silver and copper by raising with a hammer. There is not any stretch to the metal. You are just moving the metal. Or raising it upward (to the opening). Same thing applies to spinning you are raising the metal upward. This formula has been around for centuries. If you used your formula then you would need a disc 15 inches in diameter and one heck of a big lathe.
Gerald Miller wrote:
diameter.
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