[TowerTalk] New Sheaves for Crank-Up

[N3AE]

Here's a follow-up for those that might be reading this thread. Roger raises some good issues (repeated below). 

First of all, I don't intend to use nylon sheaves, but wanted to see if anyone had experience with this material. With proper fillers, nylon can be made more resistant to UV, but not enough to make me happy for this application. 

The reason I want to replace the sheaves is that one pair on the mid-section has excessive wear on one side of the groove ID. Measuring at the very top of the groove to the outside of the sheave, one sidewall is 0.010" but the other sidewall is feathered down to as small as 0.032" This is no doubt due to the fact that the axis of rotation of these sheaves is not exactly perpendicular to the line of force of the wire rope, so there's some side loading as the cable runs onto the sheave. The misalignment ia about 3 degrees. Based on careful inspection, it appears that the tower was fabricated this way and the misalignment was not created by damage. A friend who also has an EZ-Way has noticed similar sheave wear. Guess I could flip them around and let the other side wear, but much rather replace. I bet a nylon sheave with this misalignment would have one edge shaved off in short order. Maybe true for aluminum as well. 

The bearings are in reasonable shape...rotate freely with just a bit of rumble. 

The challenge in finding replacement sheaves for an EZ-Way is finding ones that are not too thick at rim or hub in order to fit into the sleeve slots on the tower. The originals (base of mid-section) measure 0.350" wide at the rim and 0.435" at the hub (across the pressed-in ball bearing). One sheave in the top section (has a smaller 3/8 inch ID bearing) is only 0.375" at the hub...thank goodness that one is OK. 

After a lot of searching I found some stainless steel sheaves with oil impregnated bronze bushings that will fit in the mid-section slots. Have not ordered them yet. Guess I'll also have to change the sheave axles from hex cap screws to shoulder bolts to keep the bushings happy. 

N3AE 





n 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)