[TowerTalk] Cabling again

Jim Thomson jim.thom at telus.net
Tue Jun 1 01:11:33 PDT 2010


Date: Mon, 31 May 2010 21:27:52 -0400
From: "Michael Ryan" <mryan001 at tampabay.rr.com>
Subject: Re: [TowerTalk] Cabling again

Steve ( for K7LXC ), As I recall the HG-70D had a 3/16 cable at the top with
1/4 for the other two levels. Does that sound correct?  Is there any reason
not to use the 1/4" cable if a different sheave and pulley is found to fit
in the upper housing?  I don't recall if the upper pulley is physically
smaller or not, but must be narrower to work with the 3/16 cable I would
assume.  - Mike
 
In a message dated 5/31/2010 5:20:02 P.M. Pacific Daylight Time,  
towertalk-request at contesting.com writes:

>  I need to re-cable a W-51, the original cable is  3/16",
for .08? more a ft., I can go with 1/4, at almost double
the  breaking strength.
The only 'weak" link I see is the pulleys,I'm wondering  what effect
the bigger cable might have on the pulleys..
any  comments?
 
    Yeah - bad idea. 
 
    And this substitution is recommended by the  manufacturer? 

##  well, UST uses  5/16"  and an 4:1 mech advantage on the very bottom section of my HDX-689. 
[ 4 x pulleys used] 
On ALL the upper sections, they use  1/4" cable  and NO mech advantage.. only ONE pulley on each of the
upper sections.  The tower weighs 5000 lbs with the PP installed and one bearing.   Toss in another
400-500 lbs for the mast + ants.   The weak link is the 1st 1/4"  cable between  2nd section from the
bottom.. and the 3 x sections [+ mast/rotor/ants]  above it.  Trying to support 3 x heavy sections + mast
/rotor/ants  with just a single  1/4"  cable is  pushing the cable to the limit imo... with no safety factor...
[and no mech advantage  either]  The cable is at 26% +   of it's rated strength.. and that's b4 ice/snow. 

I noticed they just made a recent change on their site.. and now spec NO snow [or ice].  I took down a 20m
yagi  off the top of a tower in Dec 1989.. and the damn thing weighed  at least double or 2.5 x  the normal weight.
Once I got my head above the top of the tower... you could see ice all along the tops of all els + boom.  You couldn't
see any of that from the grnd.   I lowered it down by myself.. [from the top of the tower] and the weight was un-real. 

Even fully nested, the UST  towers still have all their cables under full tension.  Now toss in the added snow/ice load
and you have a recipe for a disaster.   I'm seriously thinking of changing out at least the 1st 1/4"  cable...with
5/16" cable. [ + new  pulley, made for 5/16"].. and possibly  the other 2 x 1/4" cables as well. The width of the
4 x existing 5/16" pulleys  used on the bottom section is only 1/16" wider than  the upper 1/4" pulley.  At least
with 5/16"  cable... the load between section's 2 and section 3.. is then at 17% of the  5/16" cable.  What it really
needs is  3/8" cable.. [ then it's down to 12% of the 3/8" rating]  

BTW.. I checked some really old notes  from the late 70's and 80's.. and  saw that 3 x fellows had tried SS  cables
on crank up towers.. and all 3 of em  came crashing down !   SS  is really not made for pulley use.   It's made for
stuff like  sail boats.

later... Jim   VE7RF   






 
Cheers,
Steve     K7LXC
TOWER TECH





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