>Charles >I cannot remember the person who made this claim: ..." a piece of thick >walled tubing is stiffer than a solid rod of the same diameter and >material....therefore, boring a hole the length of the rod will increase its >stiffness." Is there any truth to this? Is it true for all metals? Can >anyone on the list verify this claim? > >Paul Chick Moment Of Inertia is used to determine relative stiffness of different cross sections in a given material. MOI of rod is (PI*diameter^4)/64, or 0.0491*doameter^4. MOI of round tubing is (PI*(OD^4-ID^4)).64, or 0.0491*(OD^4-ID^4) There is absolutely no way that drilling out a rod will increase stiffness. For a given *mass* of material, tubing will be stiffer than rod, but for a given outside diameter, rod will be stiffer than tubing. Ron N
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