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Ernest Christley wrote:
Dale Rogers wrote:
Bill,
"Case hardened" or "Through-hardened"? Either way, ditto on the cobalt drill bits, or for hole sizes larger than #20, maybe even "solid carbide".
FWIW, I do case hardening. It is typically done to give a wear-resistant surface on a part that otherwise needs to be somewhat ductile underneath - which won't be the metal's strongest state.
But do you really want to use hardened bolts anchored in aluminum? Lynn said it the other day. It would be better to choose a bolt where you could get some stretch out of it before it pulls out of the anchor material.
Ernest,
Generally, there isn't much choice. Threaded fastener specifications normally include some degree of heat-treating - hardening and then drawing the temper to achieve a "grade" of hardness. I have seen bolts made from aluminum, but I don't know as I'd want to use them on any critical component of an airplane. Yes internal threads in aluminum aren't as strong as those in steel, but we see steel cap screws in aluminum threads in all kinds of automotive applications. The strength of an internal thread in aluminum can be improved by swaging the thread with a thread-former instead of cutting it with a conventional tap.
Dale R.
COZY MkIV #0497
Ch. 12; Ch's 13, 16, 22 and 23 in-progress
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