[TowerTalk] Low Cost 20 Foot Mast

[Grant Saviers]

Another thing to note is that irrigation tubing comes in several wall 
thicknesses.

As was noted, the thinnest wall will not handle u-bolts. The tube is 
swaged into the couplings at the ends.  Unless a plug + collar can be 
machined to fit, making a  new end, best to only use the factory lengths.

One gotcha I experienced was metal fatigue, since aluminum has no 
"infinite fatigue life" stress threshold like steel.  My 80m vertical 
sections harmonically coupled between guys and fractured at the highest 
stress point. (guys were at couplings)  So guys need to be spaced 
unevenly to reduce vibration mode coupling.

The thin wall is easily damaged and dents substantially reduce the 
strength for slender column buckling.

Grant KZ1W

On 10/24/2020 20:35, Richard (Rick) Karlquist wrote:
> 
> 
> On 10/24/2020 1:59 PM, jimlux wrote:
>> On 10/24/20 1:06 PM, Tony wrote:
>>>
>> The key on stiffness is diameter - a 4" diameter thin wall tube is 
>> enormously stiffer than a 2" diameter solid bar- because it goes as 
>> the fourth power of radius.
>>
>> Rick N6RK used 4" (?) aluminum irrigation tubing for verticals.  You 
>> might be able to find it used ("Rain for Rent", for instance).
>>
> 
> Actually, the stiffness is proportional to the difference
> between the OD to the 4th power and the ID to the 4th power.
> For a constant wall thickness, this means the the
> stiffness is proportional to the mean diameter cubed.
> 
> Rain for Rent now only carries aluminum tubing at the Fresno
> store, AFAIK.  They never carried used tubing that I know of.
> 
> Any attachment to the tubing has to be in the form of a
> sleeve that wraps around it.  A U-clamp will simply collapse
> the tubing.
> 
> The verticals I have made out of irrigation tubing have mostly
> been guyed.  But I have made some that were only 30 feet high.
> But even those, didn't have anything on top.  For EME, you would
> need to use a falling derrick to erect it.
> 
> I don't know if there is any wiggle room in "I can't anchor
> guy wires to the ground", but my experience is that guyed
> masts are much easier/cheaper,stronger, etc than self supporting
> ones.  Most people underestimate the difficulty of the latter.
> 
> Rick N6RK
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