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John Cowan wrote: > > Marcus Carr scripsit: > > > Really? I'd have thought that fine pitch had better control and strength, due > > to the increased suface areas in contact, but now we're really getting OT and > > IANAE anyway. > > Fine pitch is weaker simply because the projections from the basic cylinder > are thinner. The normal failure mode for screw threads is by shearing, the limit is the surface area the force is transmitted through. If you have perfect tolerance, then the thread pitch is irrelevant, as the area parallel to the shear force is the same; if you have less than perfect tolerance, for a given absolute tolerance the area under stress is reduced less on a coarse thread than on a fine thread, so bigger screws tend to be made with coarser threads. Pete
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