[Towertalk] structural assumptions// bolts - Orion 2800

[Eugene Jensen]

The chart below gives you the middle of the road for most bolts and nut
in Metal to Metal contact as to proper Torque spec. I honestly believe
that anyone doing Tower/Antenna work should own a 3/8 and a 1/2 Torque
Wrench as the human hand isn't a good judgment tool for how tight or
loose a bolt and nut is. The Torque to yield Bolts as mention in the
below post as to Automotive Engine head's as a whole different animal
and have no real applications in Tower work. An example of a Torque to
yield Bolt is it use only once and then discarded. 73 Gene K2QWD

Max Torque (foot-pounds) for clean, dry threads Bolt size - Thread pitch
Grade 2 Grade 5 Grade 8 Special Alloy 
Grade (2)(5)(8)(SA)
1/4-20 6 10 12 14 
1/4-28 7 12 15 17 
5/16-18 13 20 24 29 
5/16-24 14 22 27 35 
3/8-16 23 36 44 58 
3/8-24 26 40 48 69 
7/16-14 37 52 63 98 
7/16-20 41 57 70 110 
1/2-13 57 80 98 145 
1/2-20 64 90 110 160 
9/16-12 82 120 145 200 
9/16-18 91 135 165 220 
5/8-11 111 165 210 280 
5/8-18 128 200 245 310 
3/4-10 200 285 335 490 
3/4-16 223 315 370 530 
7/8-9 315 430 500 760 
7/8-14 340 470 550 800 
1-8 400 650 760 1130 
1-14 460 710 835 1210 


  
-----Original Message-----
From: towertalk-admin@contesting.com
[mailto:towertalk-admin@contesting.com] On Behalf Of K7LXC@aol.com
Sent: Thursday, June 13, 2002 8:48 AM
To: W8JI@contesting.com; towertalk@contesting.com; jimlux@earthlink.net
Subject: Re: [Towertalk] structural assumptions// bolts - Orion 2800

In a message dated 6/13/02 2:13:50 AM Pacific Daylight Time, 
w8ji@contesting.com writes:

> You **must** select a bolt 
>  that, when tight, pre-loads with tension greater than the zero at the

>  minimum load condition and has know amounts of stretch, otherwise the

>  fastener will quickly work-loose or fail. (Many Caddy V-8 owners 
>  learned this when GM used the wrong headbolt design, and anyone with 
>  a race car knows it.) Virtually all automotive fasteners stay tight 
>  because of stretch, where the bolt or stud actually deforms and 
>  elongates. That's true even with lug nuts.

    Interesting info. Which brings up a question I've been looking for
the 
answer to for several years.

    I've installed numerous M2 Orion 2800 rotators over the years and 
invariably the mast turns eventually due to loosening of the mast clamp.
As 
you probably know, it's a couple of massive pieces of steel and with six

bolts it doesn't seem likely that they'll loosen up but they do. 

    I originally thought the loosening was due to temp cycling of the
big 
clamps that was the culprit. Now I suspect that it's bolt stretch that
does 
it. The nuts aren't getting loose - I've used double-nutting AND
Lok-Tite and 
the danged masts still work loose.

    First question, how do I prevent this from happening in the future?

    Second question, what's a good sequence to tighten the bolts with?
With 
six bolts (2 rows of three bolts) to do and wanting to equalize the 
tightening, I think it should be like the head of an engine where there
is a 
sequence that does that - i.e. 1-6-2-5-4-3 or something like that. 

    Third question, would torquing the nuts help? Since the tendency is
to 
REALLY (over)tighten them, maybe that's part of the problem. 

Cheers,
Steve    K7LXC
TOWER TECH -
Professional tower services for commercial and amateur
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