I am not a mechanical engineer but I do not see how an 8mm hole will weaken
your mast. I had a station that used two Yaesu G-2800 rotators and I pinned
the mast per the manufactures instructions and had no issues. Having an
antenna slip in the wind is unacceptable in my opinion. I would either
change the rotor, clamp or try pinning it. Zinc hardware corrodes very
quickly outdoors, don't use it. If you are drilling a hole why do you need
M8 hardware instead of 5/16 or even go larger which is readily available in
stainless steel. I do not believe that stainless steel bolts come in the
same grades standards as steel although some stainless materials may be
equivalent. If you drill your 4130 mast, do not run the drill too fast and
use a lubricant to avoid work hardening it. I have had no issues machining
4130/4140 using standard HSS bits.
John KK9A
To: Towertalk Reflector <towertalk@contesting.com>
Subject: [TowerTalk] To pin or not to pin
From: Rudy Bakalov via TowerTalk <towertalk@contesting.com>
Reply-to: Rudy Bakalov <r_bakalov@yahoo.com>
Date: Sun, 28 Aug 2016 16:47:27 +0000 (UTC)
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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