I would not be overly concerned with corrosion from drilled holes. The zinc
will still protect exposed metal to some extent and you could always apply
cold galvanizing to the hole. I have had to elongate many poor fitting tower
accessories and I have yet to see a corrosion problem. That said, I see no
reason to add holes when there are already bolt holes at the tower base
where a ground lug can be fastened.
John KK9A
To: towertalk@contesting.com
Subject: Re: [TowerTalk] Cadweld vs other welds or brazing
From: "Roger (K8RI) on TT" <K8RI-on-TowerTalk@tm.net>
Date: Sun, 27 Apr 2014 14:56:48 -0400
>On 4/26/2014 10:00 PM, David Gilbert wrote:
>I would agree with everything in that post except for the part about
drilling holes. I own an AN Wireless heavy duty 70 foot tower, and every
factory brace on it is held fastened to the legs >with 5/16 inch
bolts/holes. In addition, when I purchased the tower I specifically asked
Dan (who was then the owner of AN Wireless) what the constraints might be
for drilling holes in the >tower legs, and his answer was that holes of the
size normally used to receive bolts would not materially weaken the legs at
all. It's pretty much the same physics that allow us to drill >moderately
sized holes in floor joints and roof trusses without decreasing their load
rating.
You have a tower that was designed to allow for drilling the legs for
braces, most tower are not and particularly towers constructed of galvanized
tubing.
These towers are designed to use a minimum of material and depend on shape
for strength.
Drilling holes on thin, galvanized tubing invites corrosion. Yours is an
exception. I would suggest that anyone who plans on drilling, or welding to
a tower leg, first contact the manufacturer before proceeding.
ROHN specifically tells users not to drill out bolt holes, let alone, drill
new ones.
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