In Ch.10 of Edward G. HOFFMAN's book, Jig and Fixture Design, 3d ed., pp.164-167, one finds a skimpy explanation of how to design eccentric cam clamps and spiral cam clamps. What follows is my synopsis, not what Hoffman says.

In an eccentric cam, the cam is basically a disk and is rotated about an interior point (called the pivot point) other than the center. The distance between the center of the disk and the pivot point is called the eccentricity. The throw seems to be the angle one wishes to rotate the disk, but the characteristics of the end points of the rotation are not articulated. A certain change of distance associated with that rotation is called the rise but never defined. Naively, one might expect it to be the difference in the distances of the pivot point to the points on the disk corresponding to the end points of the rotation, but Fig.10-24 suggests that it might have a different meaning. The formula E=R(1-cos throw) is given, where R is the rise and E the eccentricity. The formula for the required radius of the disk depends not only on the geometry but also on the coefficient Cf of friction of the material, which is usually assumed to be 0.1. The formula is: radius=E(cos throw + (sin throw)/Cf).

For spiral cams, I think they are talking about an arc of an Archimdean spiral, viewed as a small deformation of an arc of a "base circle", and the center of rotation is the center of the spiral, which coincides with the center of the base circle. Here, the coefficient of friction doesn't enter explicitly into the formula, which says that the rise equals 0.001 x radius of the base circle x throw. But maybe the coefficient of friction is hidden in the 0.001 just as it could have been stashed in the number 0.1 in the earlier formula.

I'd like to know where these formulas are derived and explained in more detail. I'd also like to know what the German word for cam is, on the off chance that I can look this up in the Encyclopadie der Mathematischen Wissenschaften, or else a pointer to where in that reference old stuff like this might be discussed.

Ignorantly, Allan Adler snipped-for-privacy@zurich.ai.mit.edu

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