Thanks Gary,
Yes, you interpreted what I plan, correctly
I've looked at those options and they might work, but as I haven't been
able to find the cable strength, I was thinking of going the double
pulley which puts a light load on the cable and I'd not need to worry
about its strength (within reason) The 2:1 would allow most 1/4" cables
while the 3:1 should even allow using a SS cable with lots of cable lube
to keep the strands from bonding.
The stock cable is plenty long enough for the 2:1 and "maybe" the 3:1,
but definitely not the 4:1
My problem is I only have one good working arm and hand and at my age,
stamina can be a problem.
1:1 is beyond one hand. It took a Ham who is much stronger than I to
crank it up and he had to stop and rest a number of times.
I'm fairly sure I could handle the 2:1, taking 1/2 the force, but it'd
still take a lot of effort. The 3:1 (at 1/3rd the force required) would
be much easier. I could also make a simple adapter to fit a heavy duty
1/2" drill motor without having to go the the Hole Hog
The pulleys I'm using are the ones used for rescue work so they have an
extra margin of safety and are very smooth and work well with wire rope.
Galvanized? I'm not so sure. The pulleys are easily detached from the
cable and the tower allowing a quick change to the tilt over function.
On 8/27/2016 Saturday 8:56 PM, StellarCAT wrote:
If I understand you correctly why not go to a 2:1 pulley system
instead of a 4:1. Or compromise and use a 3:1! The 2:1 only requires a
pulley at the attachment point - the top return goes to the raising
fixture and the bottom goes to the winch. This will 1/2 the force on
the cable. Or a 3:1 has a pulley at each end - the initial attachment
point this time is at the tower. Again: less cable used.
I've used all three of these on raising antennas on my test tower for
range testing. The need to get 130 - 160# antennas up 12' in order to
get them on the mast that is held by a Razor - all by myself pushed me
to these options. I ended up with the 4:1 but only because it was
easier on myself - the 100' of rope needed wasn't an issue for me.
Note you'll need to add in frictional losses in the pulleys to the
equation as well - they can be quite substantial if the pulley is not
using ball bearings.
Gary
K9RX
[if I misunderstand the application - apologies.]
-----Original Message----- From: Roger (K8RI) on TT
Sent: Saturday, August 27, 2016 7:26 PM
To: towertalk@contesting.com
Subject: [TowerTalk] Strength of installation raising cable for the
LM470?
When installing the LM470 using the raising fixture, the retracted tower
is raised from horizontal to vertical. The cable attaches to the tower
roughly half way out presenting one whale of an initial load on the
cable and winch.
Does anyone have the strength listed for the original cable? It's
roughly a quarter inch galvanized steel. Unfortunately the strength for
this size and kind of cable varies widely over more than 2 to 1.
I'm planning on replacing the single straight pull with a double pulley
(rated at 32 kN = 7,193.8# )
http://www.convertunits.com/from/kN/to/pounds at the tower and a
single pulley back at the raising fixture. This means I'm going to need
a longer cable. The existing cable isn't quite long enough to make the
4 trips between the tower and raising fixture. Fortunately the new
method reduces the stress on the cable by a LOT. The cables available
at the hardware store would likely be strong enough and they do carry a
selection of strengths, although my preference is for using one of the
established cable suppliers on the net.
BTW: As for cable flexing there is the drum on the winch, the original
pulley on the raising fixture plus the 3 additional pulleys between the
tower and raising fixture. Fortunately these extra pulleys are only
used when installing, taking the tower down, or laying it down for
inspections. I would add that the larger, pulleys rated for 32kN and
up, get expensive. I did find a couple rated for 2000# at the hardware
store, but when I went back for more the strongest the had was only
rated for 800# A pair of single pulleys can be used in place of the
double pulley and the pair of those pulleys rated for 2000# was about a
quarter the list price for the Aluminum pulleys rated at 32 kN.
The multiple pulleys do reduce the linear stress on the cable, but each
time that cable goes around a pulley the strands slide back and forth
against each other, increasing wear on the cable.
I haven't been able to find the strength of the original cable. Searches
on the net have become extremely difficult. Regardless of what search
engine I use, it take me through multiple layers of other search
engines, changing what used to take a minute or two into a long, arduous
selection process.
As for rusting, or corrosion those raising pulleys don't have to be left
in place as they see so little use. Just oil them well before putting
them in storage.
73
Roger (K8RI)
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73
Roger (K8RI)
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