[TowerTalk] Making aluminum tubes telescope smoothly, with good electrical conductivity?

[Mark - AA6DX]

Kristinn ... here is what I would use ... FINGERSTOCK
http://www.surplussales.com/RF/RFFingerstk-1.html
----- Original Message ----- 
From: "Kristinn Andersen" <tf3kx at simnet.is>
To: <towertalk at contesting.com>
Cc: "'Kristinn Andersen'" <tf3kx at simnet.is>
Sent: Saturday, May 07, 2005 6:37 AM
Subject: [TowerTalk] Making aluminum tubes telescope smoothly,with good
electrical conductivity?


> Hi:
>
>
>
> I am working on an extensible vertical consisting of a 6m/18ft outer
> aluminum tube (40mm/1.5" diameter) and an inner aluminum tube that can be
> extended out of it with a motor mechanism.  For certain reasons the inner
> tube has to be substantially slimmer than the outer one, probably around
> 25mm/1" diameter.  So, to make a reasonably tight fit I will make a
> narrowing "collar" at the top of the outer tube, where the inner one will
> emerge upwards.  Furthermore, at the bottom of the inner tube I will 
> fasten
> a cylinder that almost fills the outer tube, providing mechanical
> stability there.  Sort of like a piston inside the outer tube.  Thus, the 
> mechanical
> connections or interfaces between the outer tube and the inner tube are at
> the top of the outer tube and at the bottom of the inner tube.  At these 
> key
> points I need to ensure:

> a)    Good electrical contact (so that antenna currents can continue
> from
> the outer tube to the extended inner tube;
>
> b)       Minimal mechanical friction as the inner tube is pushed up and
> retracted back down.
> Are there any suggestions on this?  What metal should I use that slides
> with low friction against the aluminum tube wall, does not corrode at the
> contact and provides good conductivity?
> 73 - Kris, TF3KX (http://www.simnet.is/net/tf3kx)