CrMo Mast/Tube - supplier in SE VK4

[VK4CZ]

Can any one in SE VK4 advise of a suitable, reputable supplier of CrMo mast/tube sections in SE VK4?

It's been nearly 10 years since the main tower was installed, and has been through many severe storms (including >150km winds in the 'Gap Storm' 6 years ago) but after being hit by a micro-cell last night the mast on tower #1 finally enabled elevation on my 20m mono and 6m 6M2WLC antenna's

The mast was a gal heavy wall 'steam pipe'... but didn't survive last nights blow,so it's time to upgrade .

[VK4TI]

Can any one in SE VK4 advise of a suitable, reputable supplier of CrMo mast/tube sections in SE VK4?

IMG_6172 2.jpg

It's been nearly 10 years since the main tower was installed, and has been through many severe storms (including >150km winds in the 'Gap Storm' 6 years ago) but after being hit by a micro-cell last night the mast on tower #1 finally enabled elevation on my 20m mono and 6m 6M2WLC antenna's

The mast was a gal heavy wall 'steam pipe'... but didn't survive last nights blow,so it's time to upgrade .

Stirlings or racetech

[VK2KRR]

Must have been a fairly big blast to bend it over like that.

I'd recommend having an aluminium outter and sleeving it. You cant really use cho-moly as a mast by itself because its too hard for mast clamps to bight into and with enough wind it will twist the antennas around.

Do you have any ideas on what size you need?

If you have another length of the steam pipe, you could probably sleeve that if you can get a fairly accurate measure of what will fit up the inside with say 1mm clearance or so.

I'm asking around re SE QLD availability. Size required will be the killer.

[VK5PJ]

Hello Scott,
Ouch that's quite a bend, that will be fun to get apart

The secret may be in gaining some extra diameter in the vertical pipe, I compiled some posts from the VK-VHF reflector some years ago where this was being discussed in depth.

http://www.users.on.net/~pedroj/towers/tower_pipe.htm

My take on this is the real strength comes in the diameter of the pipe, I have plans to change mine from 50mm to 63.5 when I need to pull it all apart.

Regards,
Peter

[VK4CZ]

Thanks Leigh, Peter & Barry

I hope (WX prevailing) and with some help that it will be on the ground later today. I'll be able to measure it all up then.

But with the hazer down, I'm seriously looking to improve the thrust bearing arrangement which will mean size can vary.

[VK4TI]

Thanks Leigh, Peter & Barry

I hope (WX prevailing) and with some help that it will be on the ground later today. I'll be able to measure it all up then.

But with the hazer down, I'm seriously looking to improve the thrust bearing arrangement which will mean size can vary.

A couple of things to remember , chrome molly will easily become brittle when welded unless cooled methodically , double seamless steam pipe with some tacs would be a better choice imho , it of course of a lower bending moment but will bend still rather than work harden . Bending saved your antennas so the safety factor worked
If you go larger and double steam tube then some button welds along the length would be advisable , take the advice of a professional welder or metal worker in your area

[VK5PJ]

Hi Barry,

If you go larger and double steam tube then some button welds along the length woulde be advisable , take the advice of a professional welder in the matter

when you say button welds, is this where you drill a small hole in the outer tube and then tack the inner to the outer in multiple places? (always keen to learn)

Regards,
Peter, vk5pj

[VK4TI]

Hi Barry,
If you go larger and double steam tube then some button welds along the length woulde be advisable , take the advice of a professional welder in the matter

when you say button welds, is this where you drill a small hole in the outer tube and then tack the inner to the outer in multiple places? (always keen to learn)

Regards,
Peter, vk5pj[/quote]
yes

[VK2EFM]

Hi All,

One obvious modification to make is slide the beams down the mast (mount the 20m monobander just above the bearing) to reduce the bending moment on the mast where it passes through the top bearing on the tower.

73,
Allan

[VK4CZ]

A huge thank you to John VK4YJV for his effort today. 6hours and yagi's on the ground without damage.

[VK3QI]

Scott,

Peter VK5PJ wrote:

"My take on this is the real strength comes in the diameter of the pipe, I have plans to change mine from 50mm to 63.5 when I need to pull it all apart."


Absolutely correct. Strength goes up the fourth power, so going from 50mm to 63 mm is (63/50)^4 = 2.5 times stronger - all other things being equal.

The actual thickness of the material makes little difference - it is the outside diameter which determines the strength.

Cheers
Peter VK3QI