[TowerTalk] Hint of the Month: Shoulder Bolts

Lee Buller k0wa@southwind.net
Tue, 17 Feb 1998 10:11:17 -0600

>Here's the problem:  The shoulder bolts had threading starting ever so
>slightly BEYOND the steel pipe.  When new, the system had points of
>contact as the smooth portion of the bolt passed through the pipe at two
>points.  Now, years later, a bit of rust had broken those points of
>contact.  The cure was to add three washers to the head side of the bolt,
>dragging the thread back toward the pipe.  Voila!  Solid contact with the
>pipe at both ends.
>A fairly subtle problem, a dramatic improvement after cure.  Lesson
>learned:  With shoulder bolts (as opposed to full thread bolts), be sure
>that you can really tighten down -- not to the end of the thread, but to
>put pressure against the surface where you need electrical contact.
>				Fred K1VR

Thanks for the information on the shoulder bolts.  I discovered these
animals a couple of decades ago and liked them for bolting masts together.
I've never used them for anything carrying RF and I can see why you had the
problem.  But they do have a place....  

I used them for masts because they are more effective and more rugged.  The
steel shaft through the holes of the masts that may be telescoped together
or use a "splint" will not allow the holes to "wallow" out for a longer
period of time.  I hope that made sense.  A regular bolt with thread going
through the hole is slightly less that the shaft of the bolt.  The play
between the edge of the hole and the thread will cause great trouble once
the mast has been tossed to and fro in the wind.  Two things happens...the
hole will enlarge over a period of time causing the beam to flail in the
wind....or the bolt will break.  They will break too.

A should bolt stops this process by allowing the builder to fill the hole
completely with the bolt shaft...thus making a very snug fit...and will not
allow the hole to wallow out.

But....  even the shoulder bolts are not the real answer to bolting together
masts.  After fighting this issue for years (I live in Kansas which a means
in the the native Kanza Indian language..."the Land of the South Wind.") I
have come to the conclustion you never splice a mast that is going to be
rotated and exposed to wind.  NEVER!  Either get a long contiguous piece of
masting material or weld it together on the tower.



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