>From the point of view of ultimate strength and number of cycles to failure,
it's probably better to get a Grade 8 bolt that has the correct (or a little
too short) length unthreaded portion, even if it's shorter than 5" overall,
than it is to get the right overall length and then to use a die to put the
extra threads onto the shank of the bolt. Real threads are rolled onto the
shank, and the forging action orients the grain of the steel such that a
rolled-thread bolt is much stronger and resistant to fatigue than one where
the threads are cut into the shank. The sharp inner edges of the threads act
as big stress risers.
Carroll Smith's book 'Engineer To Win' has some really excellent (or scary,
depending on your viewpoint) pictures comparing rolled to die or lathe cut
threads.
Best regards,
Theo
|