Hi Lee,
If your measurements are exact, then you would have what is called a "zero
clearance" fit. Not impossible, but zero clearance is at best challenging
to assemble. Aluminum telescoping tubing (for ham antennas) generally have
about 0.010" clearance between sections. Suggest to measure the two
sections more exactly with a caliper or micrometers - something that has
accuracy in the order of 1 mil, or 0.001". Tolerance variations in either
component could mean that you have exactly what you are looking for - or
even that you have an interference fit, in which case you will have
problems. Several options - (1) slit & expand the 2.5 pipe, (2) use thermal
expansion (heat the outer pipe and cool the inner pipe before assembly), (3)
create an "adapter" insert by having a shorter length of inner pipe turned
down to fit properly on a lathe, then use a 2" OD extension... I'm sure
there are other options that someone might suggest too
Generally it is a good idea to use Penatrox or similar for assembly, but
surely use a lubricant of some type so help avoid galling.
Hope this information helps you in some way & good luck on your project!
Matt
KM5VI
-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of L L
bahr
Sent: Monday, August 25, 2014 8:53 PM
To: towertalk@contesting.com
Subject: [TowerTalk] Concentric Tubing and Piping
I'm gathering parts to build a 40 meter Moxon. The boom will be 24 foot
long. I happen to own some 6 foot sections of 2.5 inch OD tubing with what
appears to have 1/16th inch wall thickness. (The stuff has never been used
but I have had it a long time. I think I bought it surplus from Hy-Gain a
zillion years ago.) That means the ID is most likely 2.375 inches. I sure
would like to use this tubing as I already own it. I need to find some pipe
or tubing to fit inside this existing tubing to join 4 sections together. I
looked for 2.375 OD tubing and can't find any. However, 2 inch aluminum
schedule 40 pipe has a 2.375 inch OD.
Would the 2 inch schedule 40 pipe bought in 6 foot sections slide and go
inside my tubing? My idea is to stagger the joints of the joiners to the
joints of the outer tubing. Maybe even have double wall throughout the
entire 24 foot boom. Would this work? I have heard telescoping tubing
actually has some gap between the telescoped parts, so they can telescope.
But, I am not sure this is true when you mix tube and pipe. That's my
concern.
Can anyone educate me on all this?
Lee, w0vt
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