Gidday,
Yesterday I was tightening by hand one of the two AN3 bolts that clamp
the flap cross tube to the articulating/hinge arms that are attached in
the floor. So, in case there is the slightest movement and this would
exacerbate in my flaps I decided to do them up "tight". Guess what, I
snapped one, yep snapped. It broke at the top of the shank where the
thread started, and did NOT strip the thread as many might have
presumed. This got me thinking that normally most bolts are designed to
effect a shear load, and not normally a clamping load. Anyway, I know
there is counter arguments to all of this, but what matters is the
applicable torque loads we use if we torque them using a wrench, and I
just stumbled upon a reference I think is important. I found this on an
VansForce website, and why it matters is the torque values are NOT for
locknuts, which have an inherent friction drag torque value of 14
in-lbs. So, referring to the attached table an AN3 needs 20-25 in-lbw,
but in actuality would be more like 34-39 in-lbs.
I think this could be easily overlooked, and if the friction drag torque
of locknuts is not taken into account, people are under torquing their
bolts.
Regards
Tony Renshaw
Sydney Aussie.
|