Bushing for Wire Rope

What about 1/4 inch nylon or polyethylene tubing, split to fit around the cable? You might be able to tack them in place with hot melt adhesive.

This is the essential gyst of what I am hoping to do, only my thinking was to fit the tube around (or at least under) the spacer, I don't think I could effectively install them on the cables do to the constraints of the block.

Sorry,

I meant short sleeves attached to the spacer that the cable runs through. Perhaps a C shaped piece, open end downward to allow the cable to contact the sheave?

THis is a classic rigging problem. Without seeing how it all goes together, my thought would be the blocks are somewhat out of alignment. If all the blocks and lines are in the correct relationship with one another, there should not be the problem of a rope jumping out of the groove. These misalignment problems are difficult to troubleshoot and someone who is well educated in rigging systems would have to observe it first hand and run through many cycles to pinpoint the misalignment. Since cost is not a consideration, I won't suggest blocks with a larger diameter sheave. Sorry I can't be more help.

The alignment is pretty good, there is a slight upward angle coming out of the sheave but it is in line with the sheave's travel. I believe the groove jumping is largely due to the general slackness of the system as our load limit/line-set is 1900 lbs divided over seven cables, with a working load limit of around 7,000lbs per cable... well the cables are a bit 'springy'.

I would have to write a thesis to prove the above statement, so let's just leave it at "I've been doing this for 20 years and have a pretty fair idea what I'm talking about"... I know that is insufficient proof, and a bit arrogant, but we aren't in a court of law...... really I just don't have the time to write one of my 20 page expositions...

Thank you for the response, you may be correct, in fact I'd wager the alignment from block to block is a little off, but these aren't precision systems and the spacer is designed to compensate for this slop.

Here is a poorly drawn schematic of the block:

This spacer is a piece of steel tube which surrounds the bolt holding the two side plates together, as the i.d. on the tube is larger than the bolt diameter there is some play. Currently many of these are too far away from the sheave allowing cables to jump between grooves (an infrequent but potentially disastrous problem) there is enough play in the spacers to rectify this problem, but as stated in the OP this leads to noise and additional wear, neither is dooming considering the location and usage, however if I can eliminate them cheaply I would prefer to do so.

please note, I mislabeled the downward line on the left hand image, this is 'batten' line 1, not 'arbor' line 1 (the arbor would be below the head block which would be located to the left of this loft block and there are 6 more loft blocks located to the right)

You mean something like this?

hmmm... if I weren't paranoid about replacing OEM parts for rigging components this would be super helpful...

I'll keep it in mind though.

Thanks

Given that the spacers are not a structural component, I really can't see replacing them with a plastic part as detrimental. but paranoia is a GOOD thing... so let's look at things that leave the spacer in place....

consider thin wall urethane tubing slipped over the existing steel spacer if you are concerned about structural integrity. or maybe heat shrink tubing. Also you could roll up thin wall teflon or mylar sheet and put it inside the spacer to take up space and prevent metal to metal contact.

I like!

How about a piece of, say, 1/2" stainless steel? You could have the ends threaded, bend it into a "U" and secure the legs in a wood block that would allow for nuts/washers above and below for adjusting the contact elevation and pressure. The stainless would be stronger than the cables (which is why I did not suggest mild steel so should withstand the rubbing.

Good idea, but it will likely still have the noise issues... at least the wear would be on an external piece instead of on the spacer.

Noise is the greater of my concerns once the spacers are properly positioned since the steel spacer is designed to be a wear point.

Just a couple thoughts.

Noise could be controlled with some grease on the cables.
Cables jumping on this sort of setup is usually caused when the backdrops or panels Hit the floor and weight is removed from the cables causing slack. (If these are fabric with no side supports it is less likely to happen.) Consider putting stops on the cables to stop the panels within 1" of the floor thus reducing the chance of jumping the grooves. Mark the lines so X point on main cable does not go beyond X point on pulley take-up system if they are manually operated. Solid panels should be attached with a flexible rope which will buckle before the cables. The pipe to which the cables are attached is usually enough weight to keep the cables taut while allowing the ropes to flex.
Hope this can help some. Good Luck

NO GREASE ON CABLES!!! Modern aircraft cable is typically self lubricating, adding grease only encourages dirt and grit to creep into the cable which: reduces it's life, makes everything it comes into contact with filthy (thereby reducing its life) and adds no practical benefit. Sorry Charsley, I don't mean to be harsh but this advice could give someone a very bad day and I am compelled to respond thusly.

The rest of your response is pretty good, but unfortunately doesn't resolve my issues for the following reasons:

Most of the time our line-sets are minimally loaded, our typical load is between 200-300lbs with 4 - 6 sets (out of 80) running around 700-1000lbs (remember: 1900lb load limit/set on a system capable of supporting ~70,000/set... 300 lbs is sort of like you holding a piece of toast), with the shortest arbor to batten cable length in a set being about 170' and the longest at around 230' there are going to be tension variances between cables which, added with the rhythmic pulsing of a man pulling a rope will manifest vibration in the cables, our system is fairly tidy but the cables still have unsupported horizontal spans of about 10-15'; this is enough, under our load conditions and considering the twisted nature of cable, for the cables to dance a little. They don't do the jitterbug or anything, but with a sheave groove only slightly deeper than 1/4" it doesn't take much for a relatively slack cable to climb on out without experiencing a shock load (i.e. hitting the floor).

Stops on the cables would also cause shock loading or, in the case of stops on the control line, broken fingers (we call these 'knuckle busters' and almost no one uses them anymore). Visual cues (e.g. marking the X's) are standard procedure; however, most of our operation occurs in near dark conditions and with a panoply of distractions for the operator (actors running around, stage hands moving things around, stage managers and other crew talking on headset about their cues...) so that even the most competent and reliable fly-man will occasionally biff it.

Thank you for your input, I do appreciate it even if I seem to be tearing it up.

Even better, a piece of UHMW which would add lubricity.

Wood still has much to recommend its use. Cost is major concern of the O.P., and it would be costly to purchase and shape the required blocks out of UHMW. Lubricity can also be obtained using hardwood, as follows:

It occurred to me after I posted my suggestion that the grain of the described hardwood blocks should be oriented towards the rim of the sheaves. Given the clearances, it's inevitable that the moving cables will intermittently contact the hardwood blocks during operation, and since endgrain is more wear resistant than side grain, endgrain orientation towards the sheaves is preferred.

Also, wood endgrain will absorb and hold a lubricant better than side grain. As I'm sure you know, wood is like thousands of tiny drinking straws bound together lengthwise. Therefore, cutting across the grain exposes the ends of these "drinking straws", creating a natural wick for lubricating fluid.

I would use dish detergent (for wood grain absorption), followed by a rubbing with a wetted bar of non-scented soap. Soap is a good theatre choice - it is clean, non-staining, non-toxic.

UHMW was my first thought, though I was thinking UHMW tube which could be fitted around the spacer... I don't think I have enough room for a standard thickness pipe wall so I came here...

GA

This should work, but I don't think it is the solution for me as manufacture and installation will be overly time consumming.

GA though

eh, maybe not... you can buy the stuff as a flat plank/sheet and use a jigsaw to cut it to width/length and then drill two crossdrilled holes for the bolts. or you could buy round bar, cut it to length and drill it (this would work really well in a small lathe with a through bore headstock, but that might not be readily available.). Nylon and acetal/delrin would also be good alternatives for this too. Teflon would probably be too soft to work as a decent spacer, it cold flows way too badly for that.

Agreed, whether wood or UHMW is used (eh), if all of the pulley blocks are identical, it would only be necessary to machine one spacer block accurately, then use it as a template for all the others. Due to the distance between the side plates (4") it would be necessary to built up the spacer block thickness with multiple layers of the chosen material. Still a bit of work, but justified. A jammed cable during a production is a disaster, and something no one should be worried about.

Here is a quick and dirty sketch (with dimensions assumed, feel free to modify as needed) of one variation I suggested:

And of course you could also use round barstock and simply cut it to length and drill a close fit clearance hole down the center too.

I see what you're doing here... I'm not sure if the spacers provide enough clearance to use this design, but next time I make that dreaded 80' climb I will look into it because these would be pretty simple to fab. and not too painful to install...

If you have access to a table saw with a dado blade you could also cut a step in the middle of the block to clear the pulley if the hole location doesn't give you enough clearance.

see, that's why I come here... smart people