Scott,
Not hex head screws. Socket head (Allen) cap screws instead. Outside
perimeter of head is round. Big difference.
6-32 for 5/8" and smaller, 8-32 for 3/4-1-1/8" and 10-32 for larger up to about
1-1/5". The head needs to clear the outer tubing so it will pinch the inner
tube against inside wall of outer tube. If you don't have means to nearly
perfectly align your drill press, you should level it as best you can in both
directions and drill with the tubes telescoped together. Then drill out one
side of the larger tubing just enough to allow the head of the screw to clear.
ONE screw per joint will do a better job than any other arrangement I have used
in 40 years of building antennas. 3 inches overlap and hole in the center -
1.5 inches from end.
My understanding is that Optibeam uses this method out of necessity because of
using metric tubing that has too much clearance for other methods. We used
this method on WRTC antennas. I would never go back to any other method of
attaching telescoping tubing.
Building you own antennas is rewarding, financially and other.
73... Stan, K5GO
> On May 8, 2019, at 9:12 PM, K9MA <k9ma@sdellington.us> wrote:
>
> I like the system used on the W3JK antenna I'm building right now. It uses
> hex head machine screws with nylock nuts (UV-proof). The hole in one side of
> the outer section is drilled larger, so the screw head clears. The screw
> sizes go from 10-24 for the 1.25 tubing to 8-32 for the smaller ones. I'm
> going one step further, and putting blue Loctite on all the screws. Needless
> to say, the screws and nuts must be stainless.
>
> That said, when I refurbished my A3 a while ago, I put sheet metal screws in
> all the joints, in addition to the clamps. I used number 6 screws, which
> seemed adequate. One could always put two of them in the larger sections.
>
> 73,
> Scott K9MA
>
>
>> On 5/8/2019 20:08, Garry via TowerTalk wrote:
>> Greetings all,
>> I am rebuilding a 17 meter beam I built about 35 years ago. At the time I
>> used slots and hose clamps where fastening element sections together but
>> this time I am going to use sheet metal screws. My tubing sizes will taper
>> from 1.125" down to .625" in 5 sections per side.
>> I can't find any information on what size screws to use unless I'm just
>> looking over it. I have seen a recommendation to use hex head screws rather
>> than typical flat blade or phillips head due to possible damage to the screw
>> head but nothing on screw size. I also wonder if self tapping would be a
>> better option than standard sheet metal type.
>> Any thoughts will be most appreciated.
>> Thanks & 73,Garry - K4OR
>> _______________________________________________
>>
>>
>>
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>
>
> --
> Scott K9MA
>
> k9ma@sdellington.us
>
> _______________________________________________
>
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>
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