(Off Topic) What Steel is used for RMC?

That's Rigid Metal Conduit.

Yes, I have searched but can't find it.

What type of steel is Rigid Metal Conduit made from? I am particularly interested in the mechanical properties.

This is for a non aviation use. I am looking for something, relatively inexpensive, to use for an antenna mast, maybe 30 feet tall. Probably two nested sizes. If I had the properties I could evaluate my options with FEA software. Wind loading would be the primary concern.

With all the expertise on here, I figured someone may know.

 

tensile strength is not always tested for, because it is not part of the specification. But apparently 30K minimum yield. Would not seem safe to bet much more on galvanized welded tube made to sell cheap as possible.
https://steeltubeinstitute.org/stee...tal-conduit-steel-rmc-for-directional-boring/

OTOH, IMC seems a little better spec'd. Don't know cost differentials
http://www.alliedeg.us/imc-just-facts/

smt

 

Thank you Aviacs!

Do you have a source for the elastic modulus?

 

what he said (without going to Machinery's to check his digits )
Any steel, any hardness.
Hardness is a proxy for strength, but youngs modulus does not change with any significance.

BTW, I'm a carpenter (& machinist) not an engineer. But have spent time working with the numbers & spec'ing material for machine designs, and for flat spring making for oddball applications.

smt

 

Chain link fence rails might work better. They have swaged end coupler to slip together. A mast needs cables at each node, I think.

 

Recreation Flying Forums (Australia based) Member Kyle Communications is an expert in this area (as the name "Communications" suggests).

You can also hook up with him on Facebook, Mark Kyle, just look for the pictures of his red and white Savannah.

 

Would like to avoid guy wires.

I have seen a design for an unguyed mast made from EMT. A crank-up mast made from nested sections. RMC or IMC would be stronger, as it has thicker walls.

 

You might want to look into the tubes used on farm field sprinkler systems. Or maybe just buy a electric company wooden post, stick one end in the ground, put your antenna on the other end.

Richard

 

$$$$$$$ (including shipping)

I can get the IMC or RMC locally for under $200.

 

3" PVC conduit is cheap.

 

It is also not usable, for the same reasons it is not used in aircraft.

 

Rohn has a 40" extensible mast. Bought one used some years ago, had a 2M, 6M, and a 440 mhz beam on top. Rotator mounted at the top, a 6' extension for the antennas. Had some Al mast material, used it for the antenna section. It was my "Rovering" antenna (we ham geeks like working from portable locations, mountain tops, etc.). If I remember correctly, Lowes had a similar mast for not much $$.

Derswede

 

Thanks, Derswede. (and I guess you mean 40 feet, not inches?)

But I was not asking for alternatives. I have already reviewed all the options. I just wanted to know the properties of RMC while reviewing my options.

And although I have plenty of room* I would like to avoid guy wires if possible.

------------
*Plenty of room for HF wire antennas. For VHF/UHF I would like to avoid long horizontal runs of feedline. Height is your friend! If I put a mast out where there is room for guy wires, then I would need about 100 feet of horizontal before going vertical!

 

Thick walled conduit, from Lowes if I recall right, is what is holding my cabin antenna up. Got it from an electrician friend who had just finished a 3 phase power install at a company. It is 2" or more in diameter and has survived several windy years up in the mountains. He had a pipe of slightly larger diameter which I set in concrete and slid the conduit into that. Has held up fine, tho it did start to rust. A paint job fixed that. Old Radio Shack rotator on top with two small vhf beams on it. HF is wire. The EMT is about 30' long, as getting it up the track to the site was a bit tough. Guess electrical supply houses would have it in that length. Heavy but the price was right. It is also unguyed. The buried base pipe if I remember right was 2.5" Dia water pipe. The conduit fit perfectly. Wiggles little even with stronger winds.

And yes, messed up on the ft/in setup. 40' mast. Straps to the side of the pickup for rovering expeditions. Gets a couple of odd looks from non-hams. I have a weighted umbrella base that I use to support it when rovering. The 220 MHz Quagi is great when that far off the ground.

Good luck with your project!

Derswede N4ABA

 

They call it rigid, but it is made for easy tight bends. I suppose it is among the softest steel available. What else do you need to know?

 

The heavy stuff is cut and an elbow is used for corners. My electrician friend does not bend the large 2" or more tubing, the 1" is always bent, but not the heavier stock. Something about number of conductors, max voltage and current meant that he had to do straight runs and use elbow couplings for corners, etc. Anyone here a licensed electrian? I will call my friend and ask him.

Derswede

 

Looks like 2 and 3" bent here:
https://steeltubeinstitute.org/steel-conduit/why-steel-conduit/advantages-2/

 

here is my .02cent idea,,,,,
one time i used the "top rail from chain link fience", it worked ok for me ,i think it come in 8 ft lenth....
....good day /rick