An interesting experience, building so many antennas. Thanks for the
support of the WRTC event.
I need some help understanding why this works better than other means
(e.g. two cross bolts)
1. it requires an expensive, hard to find drill bit, which can only be
re-sharpened cnc
2. and a second longer drill to reach the other wall, unless custom made
step/counterbore drills are used with a long enough pilot size
3. the step drills you reference drill 0.250" vs the 0.226" head
diameter of the 18-8 SHCS 6-32 from McMaster. What is the benefit of
the slop? Or were custom major diameter step drills used? I'd have to
do some deeper research, but suspect the standards don't tolerance cap
screw head diameters as tightly as screw diameters/threads. Maybe that
is why, even with a drawer full of them, I never seem to have the right
size counterbore :-(
And mechanically, what is the reasoning that it is better? (beating
rivets is easy!) Cross bolts tighten the tubes against each other in
two planes. Absolutely no wiggle. Works on large antennas.
OTOH, this may be a production manufacturer's tolerance shortcut - drill
a large hole in one side helps to insure interchange of elements, since
the outer tube holes don't need to go exactly thru the tube center. Or
if the inner tube holes are slightly off center there is enough slop for
the bolt to pass through. With a single screw, there is no hole pitch
tolerance requirement. Smaller, lighter beams made for a price point,
and limited wind - I get it.
I use two 3" or 4" Chinese cast iron v-blocks (<$20) screwed to a 24"
long plywood base to drill press drill assembled element holes, drill
first one, insert screw, turn 90 deg (visually measured), drill second.
No special drill, two steps. No hacksawing of slots for hose clamps.
These aren't cnc'd tolerances so elements are not interchangeable, but
that isn't a requirement I have for homebuilt. A volume manufacturer
would likely develop tooling to enable interchange of elements.
http://www.shars.com/products/measuring/layout-setup-tools/4-x-1-5-8-x-2-5-8-high-quality-cast-iron-v-block
Grant KZ1W
On 8/13/2015 7:20 AM, Jim Thomson wrote:
## I understand counter bore.... but how can you do a counter bore,
when the tubing thickness is paper thin to begin with... like .058
wall etc?
Jim VE7RF
-----Original Message----- From: Stan Stockton
Sent: Thursday, August 13, 2015 6:53 AM
To: Jim Thomson
Cc: <towertalk@contesting.com>
Subject: Re: [TowerTalk] Shorty Forty Hose Clamp thread
After about 40 years of making my own antennas I learned something a
few years ago when faced with assembling 65 tribanders (520 elements)
we made for WRTC2014.
I was introduced to the element joint attachment method I am told is
used by Optibeam. I was skeptical when I heard the verbal
description, having settled on pop rivets after every other
conceivable method about 20 years ago.
I made one element with pop rivets and another with a single stainless
steel socket head cap screw with a counterbore (head clearance on
socket head screw) for one wall of the larger diameter tubing for each
joint, then grabbed each one in the center and violently shook them
back and forth. The one with SHCS joints felt like one solid piece of
tubing as compared to the pop riveted one.
It is so easy and so solid, I will never mess with pop rivets again.
A V block fixture with stops, drill press and some of these bits along
with straight bits for the smaller diameter tube drilling are all that
is needed.
http://www.wttool.com/index/page/category/category_id/14686/
make the job easy in comparison to many methods. The counterbore is
important. Use stainless nylock nuts.
YMMV but I'm sold on it.
73...Stan, K5GO
Sent from Stan's IPhone
On Aug 13, 2015, at 7:42 AM, Jim Thomson <jim.thom@telus.net> wrote:
The rest of the yagi should be using 3 x rivets
at each joint.
Jim VE7RF
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