# "Kicking" Loft Blocks?



## Chris Chapman (May 24, 2013)

We had some rigging change outs this year and some of my linesets may need to be tweaked a bit. the dirty anwer has been to "kick" lift blocks upstage/downstage for a correction. I have never actually done this in all my time in Theatre, and am wondering how someone actually does this. IS it as simple as loosening the bolts of the lift block on the grid and literally kicking it to the new location? How far of a fleet angle is safe to introduce off of the head block to a lift block?


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## Footer (May 24, 2013)

*re: "Kicking" Loft Blocks?*

First, its a LOFT block, not a lift block. 

This is commonly called "kicking sheaves". It is something that if you have to ask how to do it, you really should not be doing it. Depending on how your blocks are hung it can be really dangerous to do this. Without seeing your space and how your blocks are attached to the steel it is nearly impossible to say if this is safe or not. Give a call to someone who has done this before and have them show you how to do this. 

Also, when you start doing this you kind of open up a pandora's box. In my venue we have never had to kick sheaves and I don't think they have ever moved from the day they were installed. In one of my summer stocks homes it was very routine to kick stuff around. Because of that no pipe flew perfectly straight. Everything was all kinds of out of whack. We spent at least a few hours every load in hitting sheaves to get stuff to fly right. After I left there they did a full re-rig of the place and squared all of the blocks up and I think the practice has stopped there. 

I would have a rigging company come and square your blocks up. After that, don't touch them.


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## Chris Chapman (May 24, 2013)

*re: "Kicking" Loft Blocks?*

Thanks Kyle. Loft Block is right. My caffeine for the morning hadn't kicked in yet. My local riggers are who I'd use for this for exactly the reasons you list. I want to know more about what is involved. Some of clearances between linesets are tight enough as is, and mucking up lift lines with wrong angles, and the batons no longer being parallel to plaster line is NOT a place I want to end up in.


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## tdrga (May 24, 2013)

*re: "Kicking" Loft Blocks?*

It sounds like your loft blocks are overhung (attached to the grid ribbons) instead of underhung (attached to overhead beams). If so, kicking the sheaves is the only way to move your lift lines up/downstage. With underhung lift blocks, it is possible to temporarily divert the lift lines up/downstage with a diverter or snatch block. 

On either case, it's best to have an experienced rigger come in and supervise the work. They will be able to judge what amount of adjustment is safe and prudent.

If these are permanent changes to the hang, make sure to document changes and update any paperwork. 

- Todd
Sent from a mobile device.


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## derekleffew (May 24, 2013)

*re: "Kicking" Loft Blocks?*


Chris Chapman said:


> We had some rigging change outs this year and some of my linesets may need to be tweaked a bit. ...


I hope you're not still fighting this http://www.controlbooth.com/forums/...track-vs-fire-curtain-lattice-work-fight.html battle?


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## kiwitechgirl (May 24, 2013)

*re: "Kicking" Loft Blocks?*

I spent years kicking blocks in a hemp house (the student-run university theatre) but have never had to do it in a counterweight house. In the hemp house we used to shift battens around all the time because we only had about eight (plus four winched lighting bars) and they were never where you wanted them. The real joy was that the roof was only about four feet above the grid (and the grid was not full height - 6.5 metres from stage to gallery, then 5 metres from gallery to grid), so you were bent over, and then to move the headblocks you had to lever up the sprinkler pipe to get out and replace the blocks. That theatre was demolished after the earthquakes and despite my formative years in theatre being spent in there, I'm not sorry that it's gone, it was an awful place to work. Having said that, it did teach me a lot about how to make things work with no budget and an unhelpful space, and makes me appreciate a counterweight rig and FOH catwalks a lot more!


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## Footer (May 25, 2013)

*re: "Kicking" Loft Blocks?*


Chris Chapman said:


> Thanks Kyle. Loft Block is right. My caffeine for the morning hadn't kicked in yet. My local riggers are who I'd use for this for exactly the reasons you list. I want to know more about what is involved. Some of clearances between linesets are tight enough as is, and mucking up lift lines with wrong angles, and the batons no longer being parallel to plaster line is NOT a place I want to end up in.



Long and short of it, idealy you line up your headblock the the sheaves and go from there. You can run up to a 5 degree fleet angle and get away with it. For a permant install you want to have zero fleet angle to ensure bearings don't get destroyed. If you get your first block square you can line up the rest of the blocks to that first set. It does work but in the world of lasers we now live in there is no need for that. Many overhung blocks are only secured with a clip and a clamp so moving them is rather easy. Others are not. So, can't really give you any direct answer there. I'm sure one of our guys who have a lot more installation experience will be along to help. If your having clearance issues with just soft goods you really need to have your system looked and and knocked back into square... then never touch it again (and hide the mallets!).


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## egilson1 (May 25, 2013)

*re: "Kicking" Loft Blocks?*

FYI Max fleet angle is 1.5 degrees.


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## MPowers (May 25, 2013)

A couple years ago this same topic came up on the TD group section. What follows is, in part, one of my posts on the subject. 

Kicking sheaves has been practiced as long as there has been stage rigging with a "grid", although it is slowly but surely dying out. As Derek said, there are two different rigging methods being discussed here. First the practice of "kicking" sheaves and second the use of mule blocks to redirect lift line directions to allow angled and "spot line" style rigging with a counterweight line set. This discussion seems to be centered around the questions of "What", "Why" and "Is it a good Idea". To properly discuss these topics we must first define and describe the practices, the "What" and "Why".

Both methods are a direct evolution of stage rigging from rope and pulley, to "Hemp Rigging" to line set Counterweight rigging. From the time of the Greeks and their "Deus Ex Machina", when ever there was a need for an object to be raised or lowered, a pulley was mounted where needed, a rope was strung and "Voila!" the thing raised or lowered. What today we refer to as Hemp Rigging was not a lot different at first. A number of ropes were rigged through at first a group of pulleys mounted close together and later what was called a tandem head block. At first there were no set locations for the loft blocks, they were placed on a show by show basis "as needed". As all the sheaves were individual units, and could be adjusted for angle and as fleet angle with rope rigging is not as critical or restrictive as with wire rope, the loft blocks could be placed almost anywhere. With the advent of the "Wing and Drop" style sets in the 16th century, loft blocks began to be arranged in parallel rows for each group. However at this time there were no battens as we know them today. Battens were wood boards permanently attached to a drop. Individual lift lines had a small sand bag attached when not in use and if a line was not needed for any reason, that line was simply tied off and not used. With the development of the box set in the 29th century, the parallel rows of blocks were not as useful, as many side walls were hung at angles. During the 19th century Ballet and Opera tended to stay with the wing and drop style of set with "straight" dramas or comedy's tending toward box sets, especially toward the end of the century. Box sets relied more on the spot line style with blocks positioned as needed and the only parallel rows of blocks were for the gas pipes which would eventually evolve into our current pipe battens.

When counterweight rigging was introduced in the last quarter of the 19th century, it was the first time a group of lift lines was "permanently" attached to a single batten and a single weight device. Stage technicians, designers et. al. were used to the flexibility of the hemp system and simply moved the loft blocks if it became necessary. Especially at first, line sets might be spaced at larger distances than is common today in large facilities. Unlike today's common spacing of 6" or 8", it was not unusual to have several line sets on 6" to 10" centers at the positions that often had scenic units and drops and to have two or three foot gaps to the next group. The gas and gas/electric lighting units were large and bulky and it was not unusual to move them a foot or so up or down stage to allow scenic units to clear. This was easy, especially at first, as many grids were wood and the loft blocks were only clamped or lightly bolted down. It is reported, though I can find no empirical evidence to back it up, that some blocks were held in place with large el brackets or hooks and relied on resultant force to keep them in place. Thus moving them required no tools, simply kick them as needed, and the term was coined.

As counterweight sets replaced hemp style rigging, the practice actually grew. Stage technicians were simply used to designing pick points where the scenery needed them and then adjusting as needed. As steel grids became more common and loft block attachment became more secure, the practice became a bit more labor intensive but still common, and in fact, it is still practiced in many houses today.

All the major rigging manufacturers today discourage the practice because they have no control over who does it and what their rigging knowledge and skill are. Kicking the sheaves voids the installation/labor portion of any warranty. As a result manufacturers and installers often require the blocks to be welded in place, especially in under hung situations. Under hung head blocks are almost always required to be welded after the bolt clips and final alinement adjustment is complete.

The second method of locating lift line drop points involves mule blocks to redirect the lines to the desired location. This is not only common, but the standard method for rigging circular cycloramas, orchestra shell rigging and other "non-standard" rigging uses. It is usually employed in permanent installation situations but occasionally for one-off shows that have special rigging needs. Many big budget shows with special or unusual rigging needs simply tour with their own rigging grid ( Jane Eyre or Phantom) which contains winches and chain motors where needed and then is flown from the building structure below the house rigging. When using the mule block method for temporary rigging, the lift lines change distance from the head block to the drop point, usually increasing the effective distance from the head block. This is usually adjusted for by adding additional trim chain in various lengths, as needed to equal out the lengths of the various lift lines. As a result this method is only used when there is sufficient grid height to allow the units to clear sight lines with the extra chain or where the unit is never flown above playing height. If there are unused lift lines, they are simply sand bagged to provide tension or coiled and the coil provides sufficient weight and tension to keep the line taut. I do not guarantee that is what is done in the OP's situation, but I would be interested in hearing their actual technique.

Now! Is Kicking Sheaves a good thing, a bad thing or somewhere in between? In and of itself, there is absolutely nothing wrong with "kicking Sheaves". HOWEVER ..... there are a large number of reasons why it can be a bad thing. It should never be allowed by anyone except the house staff as they are ultimately responsible for the safety, maintenance and general condition of the space. In addition, guests who kick blocks rarely replace them and they often don't tell the house staff that it has been done. Today the practice is most common in large venues with permanent rigging staff who know what they are doing and how to do it.

The things that must be observed are simple and should be obvious to any rigger, but are often overlooked by touring crews or inexperienced staff.
1. If the changed position is to be parallel to the plaster line, the short line determines the maximum distance the line set can be moved. The fleet angle is greater the closer it is to the head block.
2. Loft blocks should be angled if possible to reduce fleet angle to the minimum.
3. All bolts and clips must be fastened down to the manufacturer's recommended torque settings.
4. If the line set is never moved for the run of the show after being flown to it's trim height, fleet angles can be exceeded, but only by VERY experienced riggers with total knowledge of the loading, the angles, the properties of the specific sheaves, the off axis loading capabilities of the mounting clips, the out of axis loads imposed by the fleet angle on the sheave housing and mounting brackets and any dynamic loads that might be imposed.
5. All changes MUST be restored to the system original specs and positions with proper alignment and fastening settings when the run is over.
6. After restoring to original condition, each and EVERY component of the entire line set MUST be inspected for any changes in condition, damage or problems, and corrections made where necessary.
7. All changes, adjustments and restoration must be listed in the rigging maintenance log, dated and signed by the rigger in charge.

Note to all readers: Does your facility keep an up-to-date rigging maintenance log? Why not???

I stated earlier that the practice was slowly but surely dying out. That is because of the growth of automated rigging and the requirement of manufacturers to weld the blocks in place. Automated rigging such as package hoists do not lend themselves well to block kicking and several types, such as line shaft and Prodigy make the practice impossible.

I'm sure I've skipped parts of the equation that others will point out, if anyone has any questions, ask!


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## Chris Chapman (May 28, 2013)

derekleffew said:


> I hope you're not still fighting this http://www.controlbooth.com/forums/...track-vs-fire-curtain-lattice-work-fight.html battle?



No, but they are related. This summer my local rigging company is going to install a cover on the lattice, when we rehung our rags, our 3/4 upstage traveler moved a lineset upstage, and we gained a midstage traveler. The return sheave on both of them are contacting open linesets upstage, so two open batons need to nudge upstage a couple of inches.

(Related in that new problems reared their heads on the same project/install.)


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## BillConnerFASTC (May 28, 2013)

Chris Chapman said:


> No, but they are related. This summer my local rigging company is going to install a cover on the lattice, when we rehung our rags, our 3/4 upstage traveler moved a lineset upstage, and we gained a midstage traveler. The return sheave on both of them are contacting open linesets upstage, so two open batons need to nudge upstage a couple of inches.
> 
> (Related in that new problems reared their heads on the same project/install.)



H&H makes a diagonal dead end pulley (what I think you mean by return sheave) that is much narrower in plan. Might be easier and less likely to cause a problem than moving sets.


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## BillConnerFASTC (May 28, 2013)

I can't help but make a few comments on Michale's excellent treatise and some of the other comments.

Minor technical point, I struggle with seemingly limiting the use of the term "counterweight" to perhaps "guided arbors with ferrous weights" or some narrow group when rope and sand bags are in fact counterweight, as recognized in the PLASA rigging standard.

Not sure if it was Michael or someone else but usually rigging is either under hung or upright, and I rarely here any style referred to as overhung (just a few stagehands once in a while).

As far as spacing, not uncommon in the wing and drop era for 1" thick wood battens to bump each other. Some opera houses have sets on 4" centers. We learn from John Freeman's "On Safeguarding of Life in Theatres" - and excellent and relevant still today book available for FREE on Google books - that the Iroquois had at the time of the fire more than 10,000 square yards of canvas, 3,000 square, yards of gauze, and 8,000 board feet of dry white pine lumber, with much of this hung on over 11 miles of 5/8" manila rope treated with kerosene to preserve it in the fly loft - some 167 sets in around 50' of stage depth - close to 3 1/2" centers. I believe the Chicago Lyric has sets on 4" centers - and the sheaves are all on a common shaft hung under the loft block beams - which makes kicking more like sliding I suppose - but the intent is that multiple sets are hung and there is a triple height so you can "store" 30' drops just under the grid and completely above the drops for that night's show. (Oh yeah - double grid - so spot lines and such are from below the regular line sets and if I recall, all 3-line sets all bridled - so lost of height.

The under hung system with a grid presents a great opportunity for adjusting a set a few sets but using a small diameter divert block that attaches to the grid well - basically a sheave on an axle that clips to the well channels. in 7-8' 1.5 degrees gives you a little over 2" and I've always thought 1.5 was too restrictive and that 2.5 to 3 degrees is fine - especially for a run of a show. Somebody can look it up but I suspect that the difference between 1.5 and 3 degrees is like the difference of a wire rope lasting 20 years instead of 50, but enough people in this country seem to feel 1.5 is the limit. I think European standards are more like 2.5 or 3.


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## MPowers (May 28, 2013)

I agree with Bill's "Minor technical point,..." 100%, 'though it may be a bit pendantic. Both systems using iron or metal (not always ferrous) weights and those using bags of finely crushed silica (sand) are indeed "Counter Weight Systems". A counterweight, adjective, is any weight used to balance a load. A counter weight, noun, is a metal weight designed to fit on an appropriate weight arbor, and may be round, rectangular, cylindrical to suit. Sash weights and curtain weights, although metal counter weights, are free hung and do not fit a weight arbor, thus, by my definition, are counterweights adjective but not counter weights noun.

Bill, Thanks for the refference to Freeman's book. I read it and used its information in another time long ago and had completely forgotten about it. It was a pleasure to re-introduce it to my knowledge base.

I personally use the terms Hemp system and Counter Weight system to distinguish between sand bag and steel counterweight systems, simply because the vast majority of people I deal with, immediately know, correctly, which type of rigging system I am referring to.

I also was briefly confused with the term, "over hung", to refer to an upright system. The same poster referred to the grid steel, usually channel iron or I-Beams as "grid ribbons" a term I had not heard before. Is it possible those terms are more common in Europe or Australia?


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## BillConnerFASTC (May 28, 2013)

So when "the counterweight" is not metal on an arbor, is it not a counterweight or not a noun?

I too had never heard "grid ribbon" before.


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## MPowers (May 28, 2013)

BillConnerASTC said:


> So when "the counterweight" is not metal on an arbor, is it not a counterweight or not a noun?
> 
> I too had never heard "grid ribbon" before.



It is still a "counter weight" adjective, but not a "counter weight" noun. So a sand bag is a counter weight but not a Counter Weight. Granted, those are my definitions as I find them to be used by the general public with which I happen to deal with. UMMV.


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## BillConnerFASTC (May 29, 2013)

So I guess the concrete counterweights - on arbors on rigid guides - at Meyerson are not nouns, but adjectives. 

It's like what's a fly or the fly. Or a stage versus a platform.

Bill Conner, ASTC, ETCP Certified Rigger #28 - Theatre


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## tdrga (May 30, 2013)

MPowers said:


> I also was briefly confused with the term, "over hung", to refer to an upright system. The same poster referred to the grid steel, usually channel iron or I-Beams as "grid ribbons" a term I had not heard before. Is it possible those terms are more common in Europe or Australia?



I'm the one who used those terms- not from Europe or Australia- just Texas.

Overhung vs. upright- I guess upright is more self-descriptive- I was trying to make the distinction between the two installation methods clear and probably confused more people than helped.

Grid ribbons - when walking on the grid, the top of the c-channel is flat and long, like a ribbon. Don't know who came up with the term or where it originated. It's always been the term of reference here. Actual I-beams are identified as such - you wouldn't ever call an I-beam a ribbon.

Hope that helps-
-Todd


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## BillConnerFASTC (May 30, 2013)

tdrga said:


> I'm the one who used those terms- not from Europe or Australia- just Texas.
> 
> Overhung vs. upright- I guess upright is more self-descriptive- I was trying to make the distinction between the two installation methods clear and probably confused more people than helped.
> 
> ...



When I think of upright/overhung, I envision the blocks clamped to the grid wells - usually a pair of channels set vertically and about 10" apart - toes out - sometimes proud of the basic grid walking surface and sometimes flush. I tried to upload a photo but no luck. I can see the smaller walk on channels on their Y axis being called ribbons a little easier than the wells. Thanks for explaining.


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## venuetech (Jun 1, 2013)

MPowers said:


> UMMV.


UMMV is ?


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## rochem (Jun 1, 2013)

venuetech said:


> UMMV is ?



Perhaps "Ur _[sic]_ Mileage May Vary"? But I really hope not...


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## BillConnerFASTC (Jun 1, 2013)

venuetech said:


> UMMV is ?



Ullucus mild mottle virus*???

I really hope not this.


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## MPowers (Jun 1, 2013)

venuetech said:


> UMMV is ?



Your (U) Mileage May Vary. Meaning of course that the statement or example being referred to is not hard and fast but may well differ with any given situation.


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## BillConnerFASTC (Jun 2, 2013)

The urban dictionary and a number of sources say that would be ymmv and none suggest ummv but whatever, like, you know.


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## Chris15 (Jun 2, 2013)

The astute observer will note the proximity of the Y and U keys on a keyboard, I suspect we may be overthinking what is most likely a simple typo...


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## LavaASU (Jul 24, 2013)

*Bent Pipe*

So, theoretical question here as we've already decided to replace the bent pipes. Say you have a slightly bent pipe on one of your linesets-- no, not bent enough to be structurally compromised. Some of our spacing is as tight as 3-4" so it's hitting other pipes. What are the thoughts on adjusting loft blocks (yes, we know how) to get the pipe to clear easier? Basically pushing the blocks (and lift lines) for the bent end in the opposite direction of the bend.


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## MPowers (Jul 25, 2013)

*Re: Bent Pipe*

There are two stress points for structures, flex point and yield point. When a structure, i.e. beam, board, pipe etc., is stressed enough to deform but returns to the original configuration when the stress is removed, has reached the flex point. When it fails to return to the original condition when the stress is removed, has reached the yield point. Once a structure has passed the yield point, is is in a weakened state and even if forced back to the original shape, there is some degree of weakening. Some things, such as most pipe, retain a major portion of their strength if only slightly deformed, but now they will have a slightly lower flex and yield points. Your pipe has been weakened slightly and, depending on the degree of bend, should be replaced asap. 

Now, how to deal with it until it can be replaced? Don't move your blocks. Twist the pipe so the bend is vertical rather than horizontal. Put the bend in an "UP" position so it's own weight will tend to reduce the bend. Shorten or lengthen the trim chains as needed so all lines still carry weight. If the batten is rigged with batten clamps, just loosen them and re-tighten after twisting the pipe. If the batten is rigged with trim chains, get a couple of side arms and attach them next to a trim chain with the arm pointing up next to the lift line. Lash the side arm to the lift line to prevent the pipe from twisting back to the side ways position. NOTE: this solution is NOT a repair, it is a bandage until the pipe can be replaced.


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## LavaASU (Jul 25, 2013)

*Re: Bent Pipe*

Hey Mike,

I suppose I shouldn't have said wasn't compromised, but should have said is not compromised sufficiently to require replacement for strength. But alas its being replaced anyways. The moving the loft blocks was just something I thought about with it if we weren't replacing it. What is the reason not to do it that way?


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## Footer (Jul 25, 2013)

*Re: Bent Pipe*


LavaASU said:


> Hey Mike,
> 
> I suppose I shouldn't have said wasn't compromised, but should have said is not compromised sufficiently to require replacement for strength. But alas its being replaced anyways. The moving the loft blocks was just something I thought about with it if we weren't replacing it. What is the reason not to do it that way?



Lots of work on the restore... When you start kicking sheaves you open up pandoras box. It is never the same again unless you go up and really square everythign up. That takes a ton of time, odds are the cost of the new pipe is much cheaper then the time to square your grid.


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## LavaASU (Jul 25, 2013)

*Re: Bent Pipe*

Oh, my venue kicks blocks all the time-- fortunately the tight spacing makes it basically impossible to get too large of a fleet angle. I actually realized it was bent when I went to fix the block (it was off as well) thinking that was the issue. Yeah, that would be a seriously bad idea in a house that doesn't do that.


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## derekleffew (Jul 25, 2013)

*Re: Bent Pipe*

[Some of the above posts moved here from another location.]

1. How does (did) the batten become bent in the horizontal (US-DS) plane in the first place?
2. How does kicking sheaves help the matter, if spacing between battens is as tight as you say?
3. Can improperly aligned loft block s cause (or correct) a bent batten?
.


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## LavaASU (Jul 25, 2013)

*Re: Bent Pipe*

1. I actually have no idea how it got bent.

2. The pipe is only bent maybe 2" in the horizontal plane... but that section is either 3 or 4" centers (can't remember). That means the pipe extends 1" on one side of its center and 3" on the other (horizontally). If it's 4" centers the pipe in front extends 1" back from it's center, and this pipe 3" forward, then you have them touching. On the back side of the bent pipe you would have 2" of clearance. By shifting the bent pipe's position upstage 1", you'd end up with 1" of clearance on either side.

3. Maybe. In this case the block was about 1" off on one side (wrong direction) so I don't think its enough to have hurt anything. The type of pipe thats on that lineset is quite still. Some of ours are a different type that has more flex and appears bent in the vertical plane if the lift line tension is incorrect (fixing the lift lines fixes it).


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## ruinexplorer (Jul 25, 2013)

*Re: Bent Pipe*

Having worked in this particular theater, I can make some assumptions. The theater is a road house where many large productions come through, including the Broadway series of shows. Due to this, there are several productions that have either removed rigging to put in their own (Phantom) or many others that put in a super-structure that contains all of their own rigging. In the case of the former, most of the linesets are numbered so that they return to their original location with new points. It is possible that there had originally been vertical damage that was missed and then when replaced had put it in a horizontal position. Or, it is also possible that it was replaced in the opposite vertical position as mentioned, but not securely enough to prevent it from rolling (having some memory issues as to the rigging attachments). In the latter scenario, all linesets are gridded. However, as it is a very tight space, there's a possibility that a lineset was damaged by the super-structure and not noticed until inspection time (total speculation). This facility does get third party inspections.


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## tprewitt (Jul 26, 2013)

*Re: Bent Pipe*

Random piece of information I haven't seen posted yet: If you do move a loft block, make sure the bolts opposite the head block get pushed tight against the steel. The idea is to push it in the direction of the load so the the bolt shanks prevent it from sliding. It's a lot easier to keep something from moving than to stop it once it starts.

A useless piece of random information: Most battens will not run perfectly parallel to the plaster line. They will be off by roughly the width of the head block sheave. 0 fleet runs nice and quiet and passing lines don't tend to rub the cheeks of the loft blocks they pass. This means the end of the batten reeved to the DS groove of the head block will be further DS than the end reeved to the US groove. Some installers will line the loft blocks up in a perfect line parallel to the plaster line. I don't think this is wrong necessarily, it just doesn't run as smooth and you have to have idlers or the cables rub.


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## MPowers (Jul 26, 2013)

*Re: Bent Pipe*


tprewitt said:


> ..............................0 fleet runs nice and quiet and passing lines don't tend to rub the cheeks of the loft blocks they pass. This means the end of the batten reeved to the DS groove of the head block will be further DS than the end reeved to the US groove. Some installers will line the loft blocks up in a perfect line parallel to the plaster line..............



First, as all installers know, there is no such thing as a "perfect" line set with "True zero" fleet angle. The closest one can come is if both the head block is slightly offset (called fair lead) and the head blocks and loft blocks are angled ever so slightly so that each one is aligned directly with the groove in the matching block. Because of the gap in the lift line spacing imposed by the purchase line, either the lift line spacing has to be slightly different at that point or you have to impose a slight fleet angle. The actual "drop" points can indeed indeed be parallel to the PL. Even if installed the old school way with the head block elevated so that each line passes directly to it's loft block without idlers (which has it's own set of issues and is why we discourage this practice today). The better practice, whether over or underhung is to make the shortline block a multigroove block rather than a single groove with idlers. While this does start a small fleet angle for the lines feeding from one side of the purchase line, is is very small and can be made smaller by centering the headblock on the loft block. For example, if your short line is 15' from the head block, the greatest fleat angle (to the short and long lines)(approx 1/2" offset in 15') is .159 degrees. After the first block one "can" switch to single groove blocks with idlers, but I strongly prefer the THERN prescribed method of actually having a multigroove block at each position. The multigroove blocks actually pass the lines on closer centers than idlers and produce the smoothest running, absolute least fleet angle, installation.

Good riggers will always install a system with a slight amount of fair lead to minimize any fleet angles and allow the battens to be true parallel to the PL. I'll talk about the issues imposed by an elevated head block, why that method was introduced, and how to deal with those problems at a later date in it's own thread.


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## jwolfkill (Jul 26, 2013)

*Re: Bent Pipe*


MPowers said:


> <snipped>
> I'll talk about the issues imposed by an elevated head block, why that method was introduced, and how to deal with those problems at a later date in it's own thread.



I'm very interested to hear about this! I'll be waiting for your post . . .


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## tprewitt (Jul 26, 2013)

*Re: Bent Pipe*


MPowers said:


> First, as all installers know, there is no such thing as a "perfect" line set with "True zero" fleet angle. The closest one can come is if both the head block is slightly offset (called fair lead) and the head blocks and loft blocks are angled ever so slightly so that each one is aligned directly with the groove in the matching block.



Perhaps the intended "0 fleet" reference doesn't exist in the same way outside our own group. We use it in a casual sense to mean we have aligned as close to perfect as our tools allow. i.e. we haven't intentionally imposed any measurable fleet.

Since there is no manufacturer provided shim, the fair lead method we have interpreted as being a violation of ANSI 1.4 Paragraph 3.2.7 (e) "Mounting clips shall... They shall be installed so that the block cannot shift on the support structure." By cocking the block to the side slightly one of the mounting bolts will not touch the beam. This would allow it to potentially shift under load - thus the violation.


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## DuckJordan (Jul 26, 2013)

Not neccesarily 3 points should hold solid now less than that is be worried...


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## BillConnerFASTC (Jul 26, 2013)

I like and specify the multi line short line loft block square to headblock and then just idlers. It seems to work well.


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## MPowers (Jul 26, 2013)

BillConnerASTC said:


> I like and specify the multi line short line loft block square to headblock and then just idlers. It seems to work well.



It works out VERY well. It is, in fact, the method we/me/CLE endorse. In this case, fair lead means centering the head block on the short line loft block, which in turn is aligned with either of the outside grooves ( we prefer the DS groove just for consistency) centered on the desired distance from the PL. The long line and short line have the greatest fleet angle, as I mentioned earlier, about POINT one five nine degrees, .159d, (on a 6 line system) caused by the spacing in the head block grooves that allow for the purchase line. If each successive loft block is a multi groove block, each successive block from that point aligns the same outside groove, in our preference, the DS groove, with the desired PL to batten distance. If the lift line spacing is the "desired/recommended" 10'-0" cc. the fleet angle from block to block is .179d. If the blocks beyond the short line have idlers rather than multi groove, the fleet angle is greater, roughly .75d. as the distance from the loft block groove to the CL of the first idler is about 5 times the distance from groove to groove in a multi groove block.


tprewitt said:


> Since there is no manufacturer provided shim, the fair lead method we have interpreted as being a violation of ANSI 1.4 Paragraph 3.2.7 (e) "Mounting clips shall... They shall be installed so that the block cannot shift on the support structure." By cocking the block to the side slightly one of the mounting bolts will not touch the beam. This would allow it to potentially shift under load - thus the violation.



Notice I said the only way to achieve or approach "Perfect" Zero fleet angle rigging was to fair lead AND cant the blocks. I didn't say that canting the blocks was our method. True Fair Lead refers only to off setting the head block enough that lift lines do not abrade adjacent loft block housing in passing, not to canting or angling the individual blocks. 

There are times when canting a block (in relation to the X, Y axis of the grid steel) is the best or only choice, usually when dealing with large directional changes such as off setting the weight arbor several feet from the batten line to avoid an obstacle such as a door or similar in the same wall as the rail, or a circular cyc or when avoiding obsticles imposed by HVAC or plumbing and other building structure. When those times arise, then, shims, off set or custom bolt holes or something is done to comply with ANSI 1.4 - 3.2.7 (e) . J.R. Clancy specs actually welding the block in place in some cases. We all know Murphy, If a block CAN slip, then it WILL slip, and then, at the time most likely to cause a serious problem.


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## BillConnerFASTC (Jul 27, 2013)

No doubt the progressive loft blocks are better than single line sheaves and idlers, but it becomes a value decision. Since most of my sets are 63' battens and 7 lines, the multiline blocks add a lost of cost.

Not sure how you can be so specific about the fleet angle between head block and shout line - would seem to very a lot depending on width of stage. With a normal 95-100' wide stage, it's near 20'.

Fleeting upstage or downstage seems to have more to do with obstructions like hangers and such. I'm going to suggest that most of my systems have both - especially around odd spaced sets like electrics or main curtains that don't fall on the normal 6 or 7 or 8 inch arbor centers.


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## MPowers (Jul 27, 2013)

BillConnerASTC said:


> No doubt the progressive loft blocks are better than single line sheaves and idlers, but it becomes a value decision. Since most of my sets are 63' battens and 7 lines, the multiline blocks add a lost of cost.
> Not sure how you can be so specific about the fleet angle between head block and shout line - would seem to very a lot depending on width of stage. With a normal 95-100' wide stage, it's near 20'.
> Fleeting upstage or downstage seems to have more to do with obstructions like hangers and such. I'm going to suggest that most of my systems have both - especially around odd spaced sets like electrics or main curtains that don't fall on the normal 6 or 7 or 8 inch arbor centers.



The progressive block concept is THERN's standard, they don't do idlers. The precept is less friction in the system, closer fleet angles etc. justify the cost. And yes, it does add cost. 

The "specific" fleet angles are only examples based on a 15' distance to the first block and 10'-0" cc spacing, using dimensions from blocks grooved for 1/4" cable and 3/4" purchase line. greater distances to the first block would, of course, decrease the fleet angle, shorter distances, increase the fleet angle. 

As for when blocks must be off set and muled or angled, yes, it is usually obstructions such as HVAC, Plumbing or like a recent install where the lock rail wall was only half the stage depth. The upstage half of the stage is 40' wider than the down stage, and leads to a hallway and storage. The result was that all the arbors had to be grouped in the down stage area but the line sets went to the back wall. The result was the upstage line sets all had to be muled and some blocks had to be mounted at angles to the grid, up to 45d. Custom drilling and clips and in one case ( the 45d block) custom steel welded across the grid steel and the block mounted to that. Certified welder and Structural engineers stamp on the custom design of course. Actually for this particular job, we had an engineer do an analysis on the entire system, as I did not think the existing bar joist system was adequate for the rigging the client asked for. The result was we added panel point supports throughout and horizontal compression members between joists where we had lines muled up/down stage.

We install Clancy, H&H and Thern systems. Idlers on the first two and progressive on the latter. Both methods work just fine. Just depends on what the architect/consultant spec (if there is a consultant, note: ALWAYS have a consultant, don't let the architect talk you out of it!!!) and what the client asks for and is willing to pay for.


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## BillConnerFASTC (Jul 27, 2013)

Consultants Brannigan and Lorelli use to always design systems with progressive blocks but I think it came from Bob Lorelli's pre-consultant career with a rigging manufacturer in either DC or Pittsburg region.

The multi line short line block also guards against unexpected elevation differences between head and loft block beams - though a problem that is diminished by all underhung blocks. I miss the ease of installation and respotting sets with upright headblocks but arbor travel and economy of construction work against that arrangement.


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