[TowerTalk] Small mast design - comments?

[jimlux]

On 11/11/20 4:00 PM, Grant Saviers wrote:
> A quick look at Industrial Metal supply shows they have 0.058" wall tube 
> so sizes 1/8" different in od will telescope. (if not damaged)
> 
> Onlinemetals.com is also stocking 0.058 and 0.120 wall so for the 
> latter, 1/4" different in od will telescope.
> 
> yagimech software from DX eng can yield a good feel for the wind 
> strength and one can sleeve tubes once or twice (doable in yagimech) and 
> the strength directly adds (only true for round and square tubes). 
> Always lather up the overlap with Penetrox if you ever want to get tubes 
> apart.
> 
> Of course increasing diameter wins over more wall thickness per lb of Al.
> 
> Grant KZ1W
> 
> On 11/11/2020 15:30, jimlux wrote:
>> On 11/11/20 2:51 PM, john at kk9a.com wrote:
>>> Correct , there is a lot of tolerance on extruded tubing and it will 
>>> likely
>>> require machining to fit together.
>>>
>>> John KK9A
>>>
>>> Ron Gorski ron-n9au wrote:
>>>
>>> No. The 1-1/4 inner tube will not necessarily fit inside the 1-1/2 in 
>>> tube
>>> because of nominal manufacturing tolerances.
>>> Ron N9AU
>>>
>>
>>
>> Have you looked at using Unistrut (actually generically called "strut 
>> channel") it's pretty stiff, and a 10 foot length of the standard 1 
>> 5/8"x1 5/8" in galvanized steel is about $30.  Aluminum is about $55.
>>
>>
>> It's kind of like erector set for adults.
>>
>> There's all manner of clamps and brackets you can get for it to bolt 
>> equipment to the struts.
>>
>> There's a smaller size unistrut (low profile) which is less expensive 
>> (about 60%)
>>
>> ________




Unless there's a specific need for it to look continuous, I'd just bolt 
the two with a "lap joint". You don't need extreme strength - the 
mounting plate under the tire will fail before the tubing will, because 
of the leverage.  Figure 30 mi/hr max.

(By the way, I see lots of RVs with flagpoles at the beach that are 
substantially more than 20 ft)


Two bolts and two tubes overlapped.. ASCII art to follow


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If you're clever you could use one bolt, and then a couple ratchet 
straps on either side of the bolt to hold it straight. Put the bolt hole 
12" from the end. Stowed, it's 10 feet long, with the bolt, and the 
ratchet straps holding it to wherever you're stowing it.

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Get to where you are, unfold it

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Put one ratchet strap around the pair near the end (and 2' from the end 
of the other one).

Attach antenna, raise mast, done.

If the cost isn't excessive, I'd seriously look at the Unistrut - having 
square sides and holes makes it easy to bolt stuff to it (rotator, 
antenna) without having to use U bolts or clamps, etc.