Hi Topbanders,
With Bill VE3NH's permission I am posting his reply to me to the Top Band
listing.
--------------------
I use fine sand paper/steel wool/burnishing wheel on my drill to clean the
tubing which goes inside. I use an automotive battery terminal cleaning
tool (a tapered wire prush) to clean the inside of the larger tubing. To
fine-clean both, I use the burnishing wheel on my Dremel tool and clean
until the metal is nice and bright.
I then coat the smaller surface with a very fine coat of anti-oxidant used
in electrical connections to prevent oxidation between dissimilar metals.
When the joint has been pushed together, I use small metal screws to attach
a jumper across each joint, making sure that the screws on the top or
un-swedged section actually go through both pieces of tubing. I use tinned
braid for the jumpers, and I then paint the joint and cover the screws with
tape. If you drill pilot holes for the screws which are just slightly
smaller than the diameter of the metal screws, you don't seriously distort
the tubing and it will be possible to separate the pieces in the future.
And, using small screws does not seriously harm the mechamical integrity of
the joint.
I have used the same method of making verticals for many years and have
never had a joint fail, either mechanically or electrically. In yagi
construction I have used a similar method without the external jumper
(using stainless steel compression clamps and slotted tubing for compression
when tightened) and have had no problems running up to 600 watts. On the
lower bands I have always felt that the jumper was a sort of "safety" factor
in keeping the electrical integrity of the joint intact.
73, Bill VE3NH
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