"Kicking" Loft Blocks?
- Thread starterChris Chapman
- Start date
MPowers
Well-Known Member
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.
BillConnerFASTC
Well-Known Member
The urban dictionary and a number of sources say that would be ymmv and none suggest ummv but whatever, like, you know.
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.
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.
MPowers
Well-Known Member
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.
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.
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?
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?
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.
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.
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?
.
[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?
.
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).
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).
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.
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.
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.
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.
MPowers
Well-Known Member
Re: Bent Pipe
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.
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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Re: Bent Pipe
I'm very interested to hear about this! I'll be waiting for your post . . .
I'm very interested to hear about this! I'll be waiting for your post . . .
Re: Bent Pipe
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.
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.
DuckJordan
Touring IATSE Member
Not neccesarily 3 points should hold solid now less than that is be worried...
BillConnerFASTC
Well-Known Member
I like and specify the multi line short line loft block square to headblock and then just idlers. It seems to work well.
MPowers
Well-Known Member
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.
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
Well-Known Member
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.
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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