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Re: [TowerTalk] [Bulk] Re: [Bulk] Re: Shorty Forty Hose Clamp thread

To: Stan Stockton <wa5rtg@gmail.com>
Subject: Re: [TowerTalk] [Bulk] Re: [Bulk] Re: Shorty Forty Hose Clamp thread
From: Grant Saviers <grants2@pacbell.net>
Date: Thu, 13 Aug 2015 08:50:27 -0700
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
One other thought - if I understand correctly, metric tubing does not telescope as tightly as US 0.058/0.120" wall. So squeezing the inner tube to the far side is a way to compensate for the extra slop. A logical solution for Optibeam, but I think a bad idea if 0.058/0.120 wall tubing is available.

Grant KZ1W

On 8/13/2015 8:42 AM, Grant Saviers wrote:
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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