In an excellent study of the economics of spinning published in Metal Stamping in September, Bob Geckler, president of Torngren/Spincraft pointed out that the spinning process could be a very useful adjunct to stamping.

This could be even more the case if the art-it is by no means an exact science-of spinning was more widely understood, not only by users of metal stampings but by design and manufacturing engineers. It is a regrettable fact that the majority of engineers have little or no conception of the parameters of spinning; what can be done, what can't be done and what falls in the middle. If they are aware of spinning at all it is with a vague recollection that it's a primitive process used for making reflectors.

This lack of awareness is probably the fault of the industry itself which traditionally has been close-mouthed and reluctant to reveal its secrets. It is a sign of the maturity of the industry that this attitude has changed. With the formation of a spinning division within AMSA, lines of communication have been established and, hopefully, we can get on with the job of bringing spinning into the daylight.

To qualify as a candidate for the spinning process, a given part must have just one characteristic. It must be round. Material is not a factor because any metal that can be formed in any way can be spun. We have successfully spun coated and painted material and have had limited success with vinyl clad metals.

Volume is not a factor. With automatic equipment, very respectable production rates are possible. They are not generally equal to the production rates possible on a press but there are time savings in other areas such as tooling lead time that compensate for the slightly slower speeds. It should be noted that some dedicated, single-purpose spinning equipment is fully as fast as conventional drawing. On the other hand, when the volume is extremely low, spinning has an advantage because of the low cost of the tooling. Perhaps this would be clearer if we look at a typical low-run job.

We'll assume it's a tapered cylinder of 0.050-in. stainless steel with a height of 12 in., a major diameter of 14 in. and a minor diameter of 10 in. This would be an extremely difficult part to draw and the cost of the tooling would be very high. A typical spinning company would assign the job to an experienced spinner. (It takes from 5 to 8 years to train an all-around metal spinner.) If the volume was low-say a total of 300 pieces--he would mount a block of hard maple on the spinning lathe and would cut his chuck using conventional woodworking techniques. Then, by merely inserting a blank and switching to a spinning tool, he is ready to start making parts. If the volume were higher but not high enough to justify hard metal tooling, he might cut the chuck undersize, spin a protective shell of 3/16-in. steel over it and be ready to proceed.

The process is as quick and as simple as it sounds. What isn't simple is the technique and skill of the spinner. It looks easy but vast experience with the gamut of metals and shapes is required. Some of the spinners at Superior routinely trim blanks and shaped parts to within 0.005 in. entirely offhand. Some materials must be babied; others must be moved fast and hard to prevent work hardening.

It would be idle to claim that spinning is an all-purpose process. It is at its best as an adjunct to other processes, particularly stamping and drawing. The parts shown with this article are all the product of combined spinning and stamping. Many are high-volume items. In many cases, application of spinning technology at some point in the manufacturing process drastically reduced the cost of tooling for the draw portion of the job. MF

A. This part was produced by blanking, drawing and spinning. The body section was drawn. Welding was not permitted so the screen is literally spun into spun flange at the base of the part. It's made in both stainless and aluminum. Dimensions are 5 x 6 in. and material thickness is 0.032 in.

B. This motor cover is made from 0.060-in. steel and is 14 in. wide and 4 in. deep. The body is drawn, the flange spun and trimmed on a lathe and the piercing done on an indexing die. For very short runs, rather than set up the press, the job is completely spun using the same draw plug used for drawing on a press.