[TowerTalk] To pin or not to pin

[N2TK, Tony]

Hi Rudy,
A number of years ago I got a SteppIR original MonstIR with 3 full size
elements on 40M. I used a Prosistel 61D. I took Array Solutions advice and
bought I believe grade 8 bolts for the mast clamp and really torqued down
hard on them. I added a Teledyne Slipp-Knott and used hardened bolts.
No pinning. The mast is 2" 4130. It has not slipped to date. The original
boom to mast plate did slip once. Now the boom to mask plate is twice the
thickness and has more u-bolts mast to plate and plate to boom to keep it
from slipping. 

I don't think you can find SS grade 8 bolts. I sprayed cold zinc coat on the
bolts. I assume I will have a problem when I need to loosen the mast clamp.
That is the only hardware that is not SS except for the Rohn tower bolts. 

GL
N2TK, Tony

-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces at contesting.com] On Behalf Of Rudy
Bakalov via TowerTalk
Sent: Sunday, August 28, 2016 12:47 PM
To: Towertalk Reflector <towertalk at contesting.com>
Subject: [TowerTalk] To pin or not to pin

I am getting really tired of my mast slipping during major wind gusts. The
mast is supporting a 4 el 40m M2 yagi and a 6 el M2 KT36XA. The clamp is the
standard clamp that comes with the ProSisTel PS61D rotator.
So the question is if I should pin the mast to the rotator clamp using a M8
bolt. The clamp has 8 bolts, but clearly the friction between the clamp and
the mast is not sufficient under extreme conditions. My one and only concern
about pinning is that the hole in the mast may weaken the mast. The PST61D
is rated for 36 sq.ft so, right or wrong, I am not concerned about the wind
damaging the rotator.
If you suggest I pin the mast, there are two follow up questions:
1) What grade bolt should I use for the pin? The mast is 120K psi. Should
the bolt be rated for less (e.g., Grade 5) or more (e.g., Grade 8 or 10.9)
psi? That is, do I want the bolt to break before the mast does under extreme
conditions?
2) Further, is it OK if the bolt is zinc plated? I could not find stainless
steel Grade 8/10.9 M8 bolts. Is the contact between zinc and the mast going
to lead to corrosion?
Rudy N2WQ
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