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[TowerTalk] Crank-up mast mechanics.

To: Tower Talk <>
Subject: [TowerTalk] Crank-up mast mechanics.
From: "Roger (K8RI)" <>
Date: Sat, 24 May 2008 04:29:29 -0400
List-post: <">>
Is there a good description of the mechanics for a crank up mast on the 
web?  I'm looking at three sections or more.  I've found a couple of 
basic designs, but I haven't be satisfied with the safety aspect and 
they were basically just crank up poles.  Standard pipe (schedule 40) 
might or might not be strong enough so some sections could be schedule 
80.  In addition to the raising cable(s) there need to be guides to 
prevent each section from rotating inside the next larger size.  A 
single cable, although easy to route has to support the entire weight so 
it should have some sort of latching mechanism. (a single pulley in the 
base of each section with a single on the outside at the top of the 
section) It'd be even nicer if each section could be raised and lowered 
independently of the rest which of course would mean a winch mounted at 
the top of the previous section which would add overall weight and a 
larger wind profile. Ideally the entire mast would rotate.  Also the 
*innards* need to be accessible if the cable breaks or hangs up. 

If all else fails I can build a "rotating", fold over mast of the 
desired height that would use the support for a raising fixture which 
would be much simpler and far less expensive, but I'd really like to go 
with the crank up.  However, right now the rotating, fold-over looks to 
be much more practical and much faster to build at probably 1/3 to 1/4 
of the price for the rotating, crank-up.

I have lots of ideas and could eventually build one to easily get 60 
feet, but I'd rather not go through all the design and experimentation 
stages if the information is available.  That sort of experimenting is, 
or can be expensive. I tend to err on the conservative side so if I do 
the design it'll be far heavier than an existing design.  As it is the 
price of steel is well over twice what I was paying just a couple years 
ago and the local supplier told me to expect another 40% to 80% by the 
end of summer I need to get busy.  I used to use a lot of steel for 
building assembly jigs, tables, and other fixtures including masts and 
telescoping masts.  Even the 60' fold over is going to be a bit pricey 
just for the material.

This would replace the 25G which is replacing an old 40' Aluminum tower 
and will support the tri-bander that is now on top of the 45G which 
hopefully will make room so something on 40.
  At least that is the current thought.


Roger (K8RI)

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