[TowerTalk] Joining Boom Tubing

[Jim Thomson]

Date: Mon, 15 Sep 2014 02:02:12 -0400 (EDT)
From: "L L bahr " <pulsarxp at embarqmail.com>
To: towertalk at contesting.com
Subject: [TowerTalk] Joining Boom Tubing

I'm slowly building up a 40 meter Moxon Beam and the boom needs to be somewhere between 24 and 27 foot long depending on the article used to build it.  The boom has me stuck.  As all of you know, most aluminum is sold in 6 foot lengths for shipping purposes.  That means the tubes need to be connected.  I'm at the point where I need to determine what I am going to use for boom material and how to connect the segments.  

I have some 2 1/2 inch aluminum tubing I bought surplus many years ago.  The stuff has a wall thickness of around 1/16th inch thick and is hard aluminum, probably 6061 alloy.  I've got plenty of it in 6 foot lengths.  It's gorgeous looking tubing and I initially figured and wanted to use it for my boom material.  However, I have been racking my brain out trying to figure out how to join the sections.  (The inside diameter is around 2 3/8th inches ID.) I tried 2 inch schedule 40 pipe and it is a tad too large in diameter to fit into this 2 1/2 inch OD tubing with an approximate 2-3/8 inch ID. (I thought maybe sanding down some schedule 40 aluminum pipe but would I get it to really work?)  I thought maybe turning some oak down to a diameter to fit inside this tubing,  I have hunted high and low for some aluminum stock to either snuggly fit inside or outside this pipe with no success.  If I buy 3 inch OD tubing, it will have an ID of 2-3/4 inches.  I even thought of slicing the 
ends open in the form of a cross in some 3 inch tubing and then use hose clamps to secure things, but then the pipe would only be tight on one end of the joining pipe. I thought maybe of slicing the 3 inch pipe open along it's length and then use hose clamps to pull it tight and together again around my existing pipe.  The bottom line is I have not been able to figure out how to use my tubing satisfactorily.  I'm now starting to think maybe my tubing is not the answer for my needed boom material.  That really seems like a big waste as I know if I bought this tubing new it would run big bucks.  A 40 meter Moxon is no small antenna so the boom material needs to be decent and adequate for my purpose.

That said,  am I missing something here?  Anyone on here who could get me on a proper path?  I need to either find of way to use my existing 6 foot lengths of 2-1/2 OD tubing with a 2-3/8th inch ID or move on to something else for the boom. I'd sure appreciate hearing from you experts as my quandary has been bugging me for weeks now. Right now I am just spinning my wheels going nowhere.  I might add, I do not have a machine shop at my QTH.  I thought I would try one last time to figure out how to use my tubing before I give up on that idea by asking you guys for advice.  Any and all comments would really be appreciated.

Lee, w0vt
Houston

##  Just get the sched 40 pipe turned down on a lathe, so it will slide in nicely.   Get several  one foot lengths of the sched 40 stuff...and have each one turned on a lathe.  Then bolt the splice with 4 x .25 inch x  20 or 28  SS bolts and nylock nuts.    Or rivet each half of the splice with .187 inch rivets.   8-12  rivets on each end of the 1 foot splice.  
##  Plan B is to buy new stuff from dx eng.... which now comes in .120 inch wall thickness.   Then they all just telecope  easily.  

Jim   VE7RF