[TowerTalk] Strength of installation raising cable for the LM470?

Sun Aug 28 00:51:06 EDT 2016

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 at 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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