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.
Although I have solid copper ground wires cadwelded to the base section
buried in the concrete foundation, I was reluctant to risk the annealing
action that MIGHT occur on the tower legs above the foundation, so the
additional ground wires that I fastened to those legs (I wanted to be
able to demonstrate after the fact ... if needed ... that the tower was
grounded) were done mechanically. I used half of a galvanized pipe
ground clamp and bolted it to the tower leg, attached the ground wire to
the wire lug, and then spray painted the entire connection with
galvanizing spray. No hassles, no worries.
73,
Dave AB7E
On 4/26/2014 2:05 PM, Roger (K8RI) on TT wrote:
On 4/26/2014 1:00 PM, Warren Wolff via TowerTalk wrote:
My Tower guy wants to CadWeld my copper to the
legs of my AN Wireless tower. This worries me.
I'd pass on CadWelding directly to tower legs. CadWelding melts a goof
portion of the base metal and alloys it with the copper and the
Aluminum in the CadWeldinf material. It makes a very good electrical
joint, but would severely weeked the portion to the legs that is
melted. It also heats quie ab=n area areound the weld to red hot,
which slowly cools.
I don't know the temper of the legs, but any present temper is likely
reduced. I would neither heat the legs to a temper reducing dull
red, or hotter, nor would I allow holes to be drilled the the legs and
particularly no holes in galvanizing. ROHN specifically warns against
drilling out tight fitting bolt holes, or using the bolt to thread its
way in. To enlarge the holes, use a long taper pin with a gradual
taper. This will open the hole enough to allow "sliding" the bolt in
and leaves the galvanizing in tact! You may have to drive the taper
pin in from both directions.
As a general rule, for tower legs, don't heat, don't weld, and don't
drill.
73
Roger (K8RI)
Warren
W7WY
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