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[Towertalk] structural assumptions// bolts - Orion 2800

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Subject: [Towertalk] structural assumptions// bolts - Orion 2800
From: (
Date: Thu, 13 Jun 2002 08:48:09 EDT
In a message dated 6/13/02 2:13:50 AM Pacific Daylight Time, 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. 

Steve    K7LXC
Professional tower services for commercial and amateur

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