The clamp comes off easily as it bolts to a flat plate. The base of the
clamp is slotted to allow centering it on different size masts. The
mast plate you describe could be slotted to mount the same way in the
same place. Just weld it to the bottom of the mast
As for the 8mm hole. There will be two, one on each side. Breaking the
continuity of a circle always weakens it On a 2" diameter mast that's 10%.
Depending on the mast material, thickness, and how brittle the material
the holes weaken the mast. Being as they break the circumference in two
spots, they weaken it more than the 10%. How much more is beyond my
knowledge. Remember, we have not only weakened the mast, but are
applying force in the opposite direction with the shear pin. A reason
the shear pin must fit tightly and the hole is a smooth surface with no
rough spots to serve as the starting points for cracks.
Take an antenna that uses rivets to hold the elements together. Although
small, with the first rivet only a half inch from the end of the larger
tube, if the end brakes off, it almost always at the "single rivet" hole.
These are extremes but the small aluminum tube in the element shows that
the hole does weaken the tube. If you use two rows offset by 90
degrees, the holes in the two rows should not line up. As an example
only: If one row of 3 starts a half inch from the end and has one inch
spacing the second row should start 1.5 inches from the end. Holes need
to be clean and smooth.
Whether the weakening caused by the holes needs consideration, depends
on how close the force we are applying is to the ultimate strength of
the mast. This is where size does matter. Larger is better. Much
better. With a lot of torque, a 3" mast is much better than a 2" with a
thicker wall. Plus the 3" presents a much larger gripping surface
assuming the rotator will handle the larger size.
In most cases it's of little concern, but with large antennas weighing
several hundred pounds and long booms, the starting and stopping torque
can exert thousands of ft lbs. Then the holes need to be taken into
consideration.
73
Roger (K8RI)
On 8/28/2016 Sunday 7:59 PM, mike repinski via TowerTalk wrote:
The clamp looks like a poor design. What would be a trick solution would
machine a 1/2 thick plate that would replace the clamp and have a hole bored to
let the mast pass thru and weld the mast to the plate that would then bolt in
place of the clamp that dos not work. The only issue is you would have to take
it apart to do this.
-----Original Message-----
From: john <john@kk9a.com>
To: towertalk <towertalk@contesting.com>
Sent: Sun, Aug 28, 2016 7:44 pm
Subject: Re: [TowerTalk] To pin or not to pin
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
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
--
73
Roger (K8RI)
---
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|