[TowerTalk] Rohn 45 questions

[Stan or Patricia Griffiths]

Dennis wrote:

> I just recently purchased 11 sections of used Rohn 45.  When I got home I
> noticed that there are two different size holes in the legs for mounting
> purposes.  I was just curious why there are two different size holes ?  The
> only thing that I could think of was the larger ones was for the initial
> bolts when your high up in the air ? ? ?  Any comments ?
>
> 2nd question.  Which is the best bolt to buy for this tower:  standard one
> from the hardware shop or stainless steel ones ? ? ?  Again any and ALL
> suggestions and comments welcomed.
>
> Dennis,  W4DWS

Hi Dennis,

The safest thing to do is get replacement Rohn bolt kits.  One 45JBK contains
the six bolts and nuts necessary to join two sections.  I stock them for $3.36
per kit plus shipping.  More information at <www.reprise.com>.

Further information on this topic may interest you.  Last year, as a Rohn Tower
Dealer, I asked Rohn why they used fine thread bolts on 25G tower and coarse
thread bolts on 45G and 55G.  All they could (or would) tell me is that the 25G
was designed so long ago that nobody around now knows why they use the bolts
they specified back then!  I doubt they could really tell you any more about
why they use two sizes of bolts.  But, I have a guess:  You need enough
crossectional area in the leg bolts to prevent shearing in the worst case.
This will determine the minimum bolt size.  You don't want larger than
necessary bolts because you weaken the tower joint by drilling larger than
necessary holes through the legs.  Both bolts of the same small size would
probably not offer enough in shear and both bolts of the large size is probably
overkill for shear so, two different sizes are a good compromise.
Incidentally, the 55G tower uses two bolts of the same size as the larger 45G
bolt.

The bolts used by Rohn are what are known as "Grade 5" as indicated by the 3
hash marks on the bolt head.  Grade 5 are harder than standard hardware store
bolts but some well stocked hardware stores can supply Grade 5 if you request
it.  I would not use less than Grade 5 in this application.

Stainless steel bolts may or may not compare in strength to Grade 5.  I am not
a real bolt expert but I would not take the chance on stainless steel unless I
knew a lot more about it than I know right now.  Stainless steel bolts also
tend to "gall" or sieze up, when tightened unless the threads are lubricated.
About the only way to get a siezed stainless bolt apart is to break it (and
they seem to break a lot easier than Grade 5 bolts do, which should tell us
something . . . )

25G bolts are "plated", not hot dip galvanized like 45G and 55G bolts are.
They tend to rust fairly soon and do not seem to last nearly as long as the hot
dipped 45G and 55G bolts do.  Because 25G bolts use fine threads, I think hot
dipping them is not an option since too much molten zinc wants to stay in the
threads making them hard to install.  This is exactly why I asked Rohn to tell
me WHY they use fine threaded bolts on 25G.  If coarse thread bolts are OK for
25G, then they could be hot dip galvanized too, and 25G bolt quality would be
much better.

Well, since I could not get a straight answer from Rohn about fine vs coarse
threads on 25G, I asked a few other experts (two other tower manufacturers who
make steel towers with bolted leg joints) and neither of them could see
anything wrong with using coarse threaded bolts with better galvanizing on them
on 25G tower.

With this in mind, I also found yet another process for coating bolts with zinc
that I had NO IDEA was in use.  There is a tower company in Salem, OR by the
name of Microflect.  You have probably never heard of them since they don't
make any small stuff of interest to hams.  They make HUGE broadcast towers and
big steel supports for high tension power transmission lines.  On a visit to
their plant a couple of years ago, they showed me some of the BIG bolts they
use on their tower legs and they had the most smooth and even galvanizing I had
ever seen on bolts of that type.  It was obviously NOT hot dip galvanizing.
They use a process where uncoated bolts are put into a rotating drum with
powdered zinc and some small metal balls.  The whole mess is rotated together
for some time and the zinc is literally POUNDED onto the surface of the bolts
and completely into the threads.  The can do nuts, lockwashers, ubolts, and
just about any hardware this way.  I know it sounds like an odd way to coat
hardware with zince, but the finished items are beautiful and Microflect says
they are good enough for their huge broadcast towers.

So where is all of this leading?  I placed a rather LARGE order with their
subsidiary that sells plated hardware for bolts suitable for 25, 45, and 55 as
well as ubolts for 25, 45, and 55 rotator shelves and house brackets.  My order
should be here any day now, and when it is, I will announce it here on
towertalk.  I also plan to send some samples to K7LXC so you can hear his
opinion on this whole thing, too.  I know he says to "do what the manufacturer
says", but what do you do when they won't comment?  Personally, I consult
another expert or two, which, in this case, also happen to be tower
manufacturers.  I plan to make kits of these superior bolts available through
my web site at <www.reprise.com> in the near future.

Standby for rotating sidemounts.  I have some in stock now and am in the
process of getting them documented on the web page.  Please don't pepper me
with questions about them.  It will only delay getting the info on the web
page.  There will be complete pricing and a lot of photos.  Soon . . . very
soon.

Stan  w7ni@teleport.com


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