David & Barbara Leeson wrote:
> A few years ago, in a different context, the question of holes as
> stress risers and centers of fatigue failure was raised. Since then,
> I've seen a reference to the idea that a filled hole has much less
> susceptibility to fatigue than an empty hole. This reference was
> regarding riveting of aircraft skins.
> It makes sense that a filled hole can't deform inward, so the idea of
> filling tower-leg holes with a nutted bolt seems a good one. The filler,
> whether it's a bolt in a large hole or a rivet in a smaller one, should
> be a tight fit or the effect is lost.
> Re Rohn 45, I prefer the flat top sections that bolt onto a standard
> section. Besides giving a place to stand and work (assuming the mast
> you're strapped to is trustworthy!), it's a more flexible logistics
> situation. The thick-wall sleeves on the top plate reduce the chance
> of fatigue failure at the bolt holes, which in any event are filled by
> the bolts.
> Cheers de Dave, W6NL (ex-QHS)
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Might I suggest, for those with big loads on the Rohn tower with holes
pre drilled. Rather than put a bolt in the hole in the air. Before you
install the tower, plug weld the holes. You can re galvanize the plug
weld with "GALVO" or "REGAL" available from welding shops and any place
that does galvanizing. It's the same material used for the hot dip. You
just heat the metal with your torce until it reaches the temp to melt the
zinc bar, melt some onto the spot and use a wire brush to get even
coverage, and you're like new with no holes to worry about.
73 John K1ER
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