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

Grant Saviers grants2 at pacbell.net
Thu Aug 13 11:42:13 EDT 2015


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 at 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 at telus.net> wrote:
>>
>> The rest of the yagi should be using  3 x rivets
>> at each joint.
>>
>> Jim  VE7RF 
>
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