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Re: Bolt Tightening - Turn of the nut method

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>What I have in mind is a little different.
You're correct in saying that a given number of turns will induce a lower 
preload with aluminum flanges than with steel flanges. That's the first 
of several good reasons to avoid connecting aluminum parts with steel 
bolts. Lower preloads mean the bolts loosen faster.

If you mean that the preload is less in thinner flanges than in thicker 
flanges for a given turn of the nut, that's only true if the flange 
stiffness is more nearly that of the bolt. This is another situation to 
avoid. Flanges softer than the bolt is the main ingredient in a sure-fire 
recipe for fatigue failure.

You might want to go over the section on bolting in a machine design 
handbook with particular attention to elastic relationships between bolt 
and flange. I always thought the whole damn thing about bolt load 
invariability with applied load was nonsense until I realized what 
actually goes on.



Christopher Wright P.E.    |"They couldn't hit an elephant from
chrisw(--nospam--at)skypoint.com        | this distance"   (last words of Gen.
___________________________| John Sedgwick, Spotsylvania 1864)
http://www.skypoint.com/~chrisw


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