[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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