[TowerTalk] New Sheaves for Crank-Up

[Brian Alsop]

The problem I had with these was that the pulley wheel edges 
wore/rusted/pitted away.

Normally the shape is concave to keep the wire rope from jumping the 
wheel and getting the stuck between the wheel and sheave.

Getting a crank up tower stuck when raising or lowering means a crane job.

Had no fix. Sold the tower when I moved. New owner had his own ideas 
about how to deal with it.  This was a long time ago.

73 de Brian/K3KO

On 8/25/2013 17:24, Roger (K8RI) on TT wrote:
> On 8/23/2013 8:43 PM, N3AE wrote:
>> Hello tower experts,
>>
>> I'm in the process of refurbishing an old EZ-Way crank-up and looking
>> to replace some lift cable sheaves which have excessive wear in the ID
>> of the groves. The current 3" OD metal sheaves are sized for 3/16"
>> cable. The sheaves are rather narrow, measuring 0.38" at the rim and
>> 0.45" at the hub where the ball bearing is pressed in. The tower
>> sheave brackets will only accept a maximum sheave width of 0.50", and
>> that's tight.
>
> This is probably more for others than the original poster:
>
> As others have well stated the life problems of Nylon, my question is
> why do you want to replace the sheaves?  Are they bad, or just the
> bearings, or do you want to replace them with something more substantial?
>
> If the sheaves are OK, but the bearings are in poor shape, I'd just
> press them out and new, sealed ones in.  I assume the originals are
> sealed. Changing them only takes a small arbor press.  For those not
> familiar with pressed bearings, they need to be pressed in and not
> tapped in with a hammer.  You can do it, but risk damaging the sheave
> and giving it a permanent wobble.
>
> Brass was mentioned, but it's usually "Oil light" which is a porous
> Bronze, not Brass.  If the axle is a good fit and smooth these last
> quite well even with an off center load as long as the off axis is not
> extreme. OTOH 0.45" is getting pretty narrow for much off center load.
> I've never seen commercial bearings of regular brass although I'm sure
> they exist. I'd not expect them to be anywhere near as durable as "oil
> light", or bronze bearings which you mentioned with SS sheaves.
>
>    Unless the originals have a history of problems, I'd stick with them.
> It sounds like the hub is already as thick as you can get, so you'd gain
> little but appearance with a wider rim.
>
> 73
>
> Roger (K8RI)
>> While looking at McMaster-Carr's web site (
>> http://www.mcmaster.com/#wire-rope-sheaves/=o71onb ), I was surprised
>> to see Nylon sheaves for wire rope applications. For the size I'm
>> looking for, they have the same load rating as the metal sheaves shown
>> near the top of the web catalog page.
>>
>> Does anyone have experience with using Nylon sheaves in the lift
>> systems for crank-up towers? Somehow, this seems wimpy to me, but they
>> do meet my max width requirements and have the same load ratings as
>> similar sized metal sheaves.
>>
>> I've found another source that has what I need in stainless steel
>> (with a bronze bushing rather than a ball bearing), but still curious
>> about the Nylon.
>>
>> Thanks
>>
>> Shawn - N3AE
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