Sheave Diameter Conundrum

[Dacheeseman1928]

Hey Friends,

Recently I had an issue with one of my flying rigs that caused my cable to deform. After talking to my rigging supplier and some local pros (that have been doing this a lot longer than me) we concluded that it was due to my sheave diameter being too small. I was using 2" diameter sheaves with 1/8" AC cable. According to my rigging supplier and my Stage Rigging Handbook the correct sheave diameter for 7x19 1/8" cable is 3 3/4" (.125 x 30 = 3.75).

My mission now; finding pulleys that have correctly sized sheave for 1/8"cable. I have searched far and wide but was unable to find a pulley that had the proper dimensions. The best I could find was a pulley with the correct diameter but the grove is sized for 3/8" cable and it was well outside my price range (cheapest was still around $400). On top of this it seems most pulleys have a diameter that is too small for the cable size it is designed for.
I find it strange that there is so much hardware out there that doesn't meet this standard. It also seems odd that I'm the first person to discover this. Is there something I'm missing? Can someone explain this to me?

Follow up question; what kind of pulleys do you use when you are rigging small units (<75 lbs.) that only require 1/8" cable.

Cheers

 

[BillConnerFASTC]

In my experience not a common size wire rope for stage rigging but, H&H Specialities has a couple of blocks:

As does Clancy

 

[BillConnerFASTC]

I see Fehr also has some.

 

[RonHebbard]

Hey Friends,

Recently I had an issue with one of my flying rigs that caused my cable to deform. After talking to my rigging supplier and some local pros (that have been doing this a lot longer than me) we concluded that it was due to my sheave diameter being too small. I was using 2" diameter sheaves with 1/8" AC cable. According to my rigging supplier and my Stage Rigging Handbook the correct sheave diameter for 7x19 1/8" cable is 3 3/4" (.125 x 30 = 3.75).

My mission now; finding pulleys that have correctly sized sheave for 1/8"cable. I have searched far and wide but was unable to find a pulley that had the proper dimensions. The best I could find was a pulley with the correct diameter but the grove is sized for 3/8" cable and it was well outside my price range (cheapest was still around $400). On top of this it seems most pulleys have a diameter that is too small for the cable size it is designed for.
I find it strange that there is so much hardware out there that doesn't meet this standard. It also seems odd that I'm the first person to discover this. Is there something I'm missing? Can someone explain this to me?

Follow up question; what kind of pulleys do you use when you are rigging small units (<75 lbs.) that only require 1/8" cable.

Cheers

@Dacheeseman1928 You MAY find a useful selection amongst aviation manufacturing and service companies; their sheaves are not only very well made / reliable but also often comparatively light weight. I suspect they won't be cheap.
Toodleoo!
Ron Hebbard

 

[DrewE]

@Dacheeseman1928 You MAY find a useful selection amongst aviation manufacturing and service companies; their sheaves are not only very well made / reliable but also often comparatively light weight. I suspect they won't be cheap.

If you don't know where to look for aviation parts, one of the large standard suppliers is Aircraft Spruce and Specialty. https://www.aircraftspruce.com/menus/ap/pullies.html is their page of pulleys; the phenolic and aluminum lines look like there are some that would be suitable, but you'd have to work out suitable mounting brackets etc. The phenolic ones strike me as fairly reasonably priced (especially for aircraft parts). I think these would have traceable certifications as to their working loads etc.; safety-critical aircraft components generally do, and it's hard to imagine too many small aircraft parts more safety critical than components in the primary flight control systems.

 

[RonHebbard]

If you don't know where to look for aviation parts, one of the large standard suppliers is Aircraft Spruce and Specialty. https://www.aircraftspruce.com/menus/ap/pullies.html is their page of pulleys; the phenolic and aluminum lines look like there are some that would be suitable, but you'd have to work out suitable mounting brackets etc. The phenolic ones strike me as fairly reasonably priced (especially for aircraft parts). I think these would have traceable certifications as to their working loads etc.; safety-critical aircraft components generally do, and it's hard to imagine too many small aircraft parts more safety critical than components in the primary flight control systems.

@Dacheeseman1928 and @DrewE When the shop I was with was supplying and finessing the first AC servo automation drives on Broadway, we were using phenolic sheaves from the aircraft industry for all of our custom 'in deck' track drives. At the time all of the other automation shops were supplying DC and DC servo drives. Feller Precision cross-rented one of our AC servo drives for the accurately positioned high torque it provided within a very limited space within a comparatively shallow show deck. I don't believe any of the phenolic sheaves ever gave us any trouble.
Toodleoo!
Ron Hebbard

 

[What Rigger?]

Flying rig? Could you elaborate?

 

[Dacheeseman1928]

Flying rig? Could you elaborate?

Of course! In short, it's a slang term I use for spot rigging. The theater I work for doesn't have a fly system. Over stage we have a catwalk system that gives us access to high steel left over from a pipe grid system we had before we got catwalks. This high steel is what we rig from. If we ever need something to fly we install pulleys where we need them (more often where the high steel allows us too) run lines and so forth. Basically we build a single line set where we need them for each show. Since it's usually just one line set (or sometimes just one line) I feel inaccurate calling it a fly system. So I started calling it a rig instead.

p.s. Sorry for the delayed response. I'm sure you all understand when things get busy and blah blah blah. Thanks for the info above! It's been useful.

Cheers!

 

[Van]

Of course! In short, it's a slang term I use for spot rigging. The theater I work for doesn't have a fly system. Over stage we have a catwalk system that gives us access to high steel left over from a pipe grid system we had before we got catwalks. This high steel is what we rig from. If we ever need something to fly we install pulleys where we need them (more often where the high steel allows us too) run lines and so forth. Basically we build a single line set where we need them for each show. Since it's usually just one line set (or sometimes just one line) I feel inaccurate calling it a fly system. So I started calling it a rig instead.

p.s. Sorry for the delayed response. I'm sure you all understand when things get busy and blah blah blah. Thanks for the info above! It's been useful.

Cheers!

So for loft blocks are you just running individual single pulleys each with an offset?? What are you doing for Head blocks?

 

[Dacheeseman1928]

So for loft blocks are you just running individual single pulleys each with an offset?? What are you doing for Head blocks?

Oddly I don't have to offset the pulleys because we operate our flys from upstage (we also don't have any wing space). But yes single pulleys for loft blocks. For a head block I also use single pulleys. I just put them close together. I wish I could use a real head block or even a double pulley but the fleet angle is way too severe.