re: bolts and nuts

[bearbvd@domain.elided (Greg Hermann)]

At 10:21 AM 12/30/02, Dana Loomis wrote:
>Greg Hermann wrote:
>
>>Standard (good) design practice with studs installed in castings is to use
>>a course pitch thread on the end in the casting and a fine pitch thread on
>>the end meant to accept a nut.
>>
>>This becomes emphatically true when dealing with a light alloy casting.
>
>Perhaps he'd also be willing to explain why is this so important.  I'd like
>to understand.
>
>Dana Loomis

Course pitch threads are much stronger (in tension) and also considerably
more difficult to gall (strip) in a casting than fine pitch threads are.
This is due to the brittle, sometimes porous nature of almost any casting,
as well as to the softness of aluminium castings.

A fine pitch thread requires less torque to develop the same clamping force
compared to a course pitch thread--so, using a fine thread on the outer end
of a stud puts less torsional stress on the stud and casting when the nut
is tightened sufficiently to achieve a given (design) clamping force.

Greg
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