[TowerTalk] Rigid Steel Conduit as Mast?

[Roger (K8RI)]

jimlux wrote:
> Roger (K8RI) wrote:
>>
>> Jim Brown wrote:
>>> I asked a colleague who builds a lot of commercial two-way 
>>> installations where I could find 2-inch hot-dipped galvanized mast 
>>> material locally. He suggested that I use 1.5-inch rigid steel conduit.
>> There are two types of rigid steel conduit. The one is like schedule 
>> 40 pipe and the other (EMT) is thin wall.
>> The heavy conduit like we used in industry is soft like water pipe, 
>> but still fairly strong.  Then there is thin wall or EMT which would 
>> probably work IF the antenna is mounted right at the top of the 
>> tower. I would not want to mount the antenna any distance above the 
>> top of the tower due to the leverage or angular moment generated 
>> particularly due to wind load.
>>
>> 73
>>
>> Roger (K8RI)
>
>
> I've used EMT as a (poor but expedient) structural material for things 
> like tents and geodesic domes..
> here's my observations:
> a) It's crummy quality steel and highly variable in material 
> properties to boot.
> b) It has a very obvious weld, which protrudes variably into the middle
> c) It bends once or twice, if properly jigged and supported (after 
> all, this is what it's made to do)
> d) it cracks along the weld, or the ends, etc.  Don't expect to be 
> hammering the end flat to make a flange you can bolt through.  Or, at 
> least, don't expect that flat end to be pretty and not cracked.
> e) it's quite malleable.. not at all springy, so if you load it, it 
> bends, and stays bent.
>
I'd add

    f.)  It won't last long out in the weather.
I've used it to build relatively small H-frames for UHF quadrature 
arrays about 10' x 10'.
They rust almost as fast as cad plated bolts. OTOH they still last quite 
a few years if given a good coat of epoxy paint while still nice and clean.

73

Roger (K8RI)
> On the other hand, it's incredibly cheap. So for a field expedient 
> mast or something like that, I'd use it again.  Just don't expect it 
> to be rugged and long lived.  You could throw up 30-40 feet of 3/4" or 
> 1" EMT with some lightweight rope guys for a few bucks.
>