[TowerTalk] Choice of aluminum

[Grant Saviers]

DX Engineering sells Yagi-Mech which calculates wind loads for yagi 
elements.  Generally, gravity is less stress than wind so you can get 
some estimates of what is needed for diameters and wall thickness for a 
self supporting vertical.   (zero wind will reveal the gravity stress 
levels).

A problem with stock tubing from mass metal suppliers is a .250 wall is 
.250 +/- some tolerance which may preclude telescoping at the stepped 
diameters.  You won't know until you try it for each tube. Note that DXE 
(and Texas Towers) sells tube made especially for telescoping and the 
walls thickness is reduced appropriately so the draw tolerance can be 
accommodated.  I've asked DXE for longer lengths than catalog - no 
dice.  Apparently, they have to order mill lots to get the thinner wall 
and have it cut to length by the supplier.  I've found that the 
"guarantees telescoping" wall thicknesses are hard to find in stock at 
Jorgensen, Tube Service, Thyssen, etc., but it is always worth a call as 
they can check the entire USA inventory online.  You always have the 
choice of machining some couplers from very thick wall material, also 
known as Holobar.  The good news is onlinemetals.com stocks a lot of 
sizes and will sell it in 12" lengths.

My former QTH 80m top loaded vertical failed from fatigue after 6 years 
since I guyed it at the top and 50% - a bad idea as it oscillated like 
crazy in winds greater than 15kts.  So plan to guy at heights that won't 
couple oscillations between sections through guy points.  My failure 
point was like it was laser cut.  Note that Al has NO threshold fatigue 
stress level, whereas steel has a threshold that if not exceeded the 
fatigue life is infinite.

Consider what it will take to erect the mast - a 50% height falling 
derrick will likely work or a sign truck crane might be able to handle 
the weight.  Or rent a 40' 4WD boom lift as they usually have 500# 
capacity so you and the mast hopefully won't exceed that ;-) .  They're 
a lot of fun/exciting and easy if you go slow and get the delivery guy 
to give you the basic operating course.

Grant KZ1W


On 10/13/2012 5:02 PM, Jorge Diez - CX6VM wrote:
> Hi Rudy,
>
>   
>
> You are lucky!, I am considering something for CW/SSB J
>
>   
>
> There´s some commercials self supporting towers. Also a Rohn 25 is good for
> a guyed tower. My problem is shipment cost and handling.
>
>   
>
> So looking for instructions about how to build one J
>
>   
>
> 73,
>
> Jorge
>
> CX6VM/CW5W
>
>   
>
> De: Rudy Bakalov [mailto:r_bakalov at yahoo.com]
> Enviado el: sábado, 13 de octubre de 2012 21:46
> Para: Jorge Diez - CX6VM; TexasRF at aol.com; towertalk at contesting.com
> Asunto: Re: [TowerTalk] Choice of aluminum
>
>   
>
> Jorge,
>
>   
>
> This is a great question that has been on my mind for a while. I was very
> tempted to try to model it, but never found the time to do so. I also
> thought that all I care about is the CW/RTTY portion of 80m.
>
>   
>
> That said, I decided to see what DX Engineering offers on their site for 80
> m. Two very interesting observations from the 80m vertical installation
> manual:
>
>   
>
> 1) they use very small size tubing, not even close to what I am considering
> (my current 40m vertical uses better tubing!!!)
>
> 2) they claim a very wide bandwidth
>
>   
>
> So if their 80m verticals are half as good as they claim, the much beefier
> size tubing I am considering should do very well.
>
>   
>
> Rudy N2WQ
>
>    _____
>
> From: Jorge Diez - CX6VM <cx6vm.jorge at gmail.com>
> To: 'Rudy Bakalov' <r_bakalov at yahoo.com>; TexasRF at aol.com;
> towertalk at contesting.com
> Sent: Saturday, October 13, 2012 7:36 PM
> Subject: RE: [TowerTalk] Choice of aluminum
>
>
> Hello Rudy
>
> What´s the bandwidth of this verticals compare with towers?
>
> 73,
> Jorge
> CX6VM/CW5W
>
> -----Mensaje original-----
> De: TowerTalk [mailto:towertalk-bounces at contesting.com] En nombre de Rudy
> Bakalov
> Enviado el: sábado, 13 de octubre de 2012 21:04
> Para: TexasRF at aol.com; towertalk at contesting.com
> Asunto: Re: [TowerTalk] Choice of aluminum
>
> Gerald,
>
> Thanks for the comprehensive answer. I didn't realize that 6061-T6 is more
> expensive than 6063 as I was looking online prices in chunks of 12 and 24'.
>
> Just for kicks I prices a 4-Square set of verticals made of 24' sections of
> 3", 2.5", and 2.0", 0.25" wall thickness. $2,300 delivered for the set.
> Doesn't look that bad compared to dealing with towers and tower crews.
>
>
> Rudy N2WQ
>
>
> ________________________________
> From: "TexasRF at aol.com" <TexasRF at aol.com>
> To: r_bakalov at yahoo.com; towertalk at contesting.com
> Sent: Saturday, October 13, 2012 6:36 PM
> Subject: Re: [TowerTalk] Choice of aluminum
>
>
> Hi Rudy, 6061-T6 aluminum has a yield strength rating the same as 6063-T832
> that is sold by Texas Towers and others.
>   
> The 6061-T6 costs more than 6063-T832 because of the extra
> heating/quenching steps needed to reach the rated yield strength. 6063-T832
> reaches the rated yield strength by work hardening the material in the
> drawing
> process.
>   
> If you want a self supporting vertical, then you would need to go through
> the same process as designing a 80 meter beam element with most of the
> material
> weight left out of the calculations. Just as a guess I would expect the
> bottom
> section to be about 4" diameter with a .25" wall.
>   
> This is not a trivial structure! Please proceed with caution!
>   
> If you want a guyed vertical, there are a number of them that have been on
> the air long enough to think about duplicating one. W5UN is one that comes
> to
> mind.
>   
> 73,
> Gerald K5GW
>   
>   
>   
>   
>   
> In a message dated 10/13/2012 4:09:30 P.M. Central Daylight Time,
> r_bakalov at yahoo.com writes:
> I was  wondering if anyone can help me select the right material for
> full-size 80m  verticals. My questions are as follows:
>> 1) metalsupermarkets.com offers
>    6061-T6 aluminum, but not T8. Is there a difference between T6 and T8 for
> my
>    purpose?
>> 2) Should go for the 0.125 or 0.065 wall thickness?
>> 3) Is 1"
>    tubing OK for the topmost segment? Too stiff for the wind at 70'? Not
> strong
>    enough?
>>
>> I am aware that many ham stores offer 6061-T8 tubing, but I
>    do want to buy it local in VE3, close to my QTH, in 12' lengths (instead
> of
>    6') and avoid shipping complications due to length or clearing
>    customs.
>> 73 Rudy
>    N2WQ
>> _______________________________________________
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>>
>>
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