# Grid Height



## Reynolds (Feb 21, 2010)

Hello,

I've been working for the past few weeks on developing a reference card for my school's theater, with information such as the dimensions of the deck, how many dimmers are working, etc., etc. When our theater was built, the company that installed our fly system didn't leave anything permanent with our fly specs at the rail. We recently weighed our bricks because weighting has seemed off for years, and found out that we had been told the wrong weights by the previous consultant we had on fly safety.

To avoid any mistakes like that in the future, we're taking another look at everything on our rail.

To that extent, I was wondering a few things:

A: What is the correct method to weigh a batten?

B: When measuring our grid height, is it the height of the physical grid, or is it the height that our battens are when all the way out?

Any help is appreciated.


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## derekleffew (Feb 21, 2010)

A. One can look up the per foot weight of 1.5" Schedule 40 or Schedule 80 steel pipe, but the exact weight is not really important. A batten is considered "in weight" when 1) the arbor and batten are at the same height AND 2) it takes an equal amount of force to move in either direction. One adds or subtracts as many bricks, half-bricks, and wafers as necessary to accomplish this. Most venues paint the "pipe weight" bricks a distinct color, and it is understood that these are rarely, if ever, to be removed.

B. Have a look at the Collaborative Article Venue Tech Info Packet. "Grid Height" and "Batten Maximum High Trim" are usually noted as two separate specifications.


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## Reynolds (Feb 21, 2010)

Thanks for your help.


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## BDS0111 (Feb 21, 2010)

Be sure to include the following measurements in regards to your grid height and pipe trims: Minimum Trim Above Stage, Total Pipe Travel, Maximum Trim Above Stage, Height to Grid Floor, and Headroom Between Grid and Roof. Also, list whether your lofts blocks are grid mounted or underhung from the ceiling.

Hope this helps!


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## MPowers (Feb 21, 2010)

Grid height usually refers to the walking surface of the steel, but not always. 
Some places lit the underside of the lowest support beam that runs under the grid. Knowing both is a good thing. Other things to list are Batten length, batten material (1 1/2" sched 40 pipe or......, lift line spacing, Arbor height, all the things just mentioned by the previous post, overhang length from the long and short lines to the batten end. Manufacturer of the system if known, installing company if known, date of install, last date inspected. System loading capacitys, that is, max load for any lineset and max point load at any lift line determined by the individual loft block specs. Max point load between lift lines is determined by batten material and spacing between the lift lines. Age of system, age and type of purchase lines. 

Michael Powers, Project Manager, ETCP Certified Rigger-Theatre
Central Lighting & Equipment, Inc., Des Moines, Iowa, Central Lighting & Equipment


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## Reynolds (Feb 23, 2010)

Thanks for your help guys.

MPowers: Is there a general rule of thumb for inspection frequency? Seeing the condition of some of our auditorium, I wouldn't be surprised if there has been no inspection since installation about 17 years ago. We have a few professionals who stop by occasionally, and know enough that getting a qualified inspector wouldn't be any trouble.


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## MPowers (Feb 23, 2010)

Permanent rigging installations should be inspected *at least* once a year. If you do 4 shows a year with 20 performaances each, that is often enough. If your venue runs events 250 or more nights a year with many cues or rigging moves, then it should be about twice a year. Ultimately the frequency of use and type of use, such as how many in-show cues.... few, mostly at the in and out or "A Lot" , what is speed of travel during cues, slow like a sunrise or fast like a yo-yo, what are the loads, light or heavy...etc. all these will add up to what is the right inspection interval for any given house. The rule of thumb you are looking for is "Once a year at least and more often as dictated by usage". Hope this helps.

Michael Powers, Project Manager, ETCP Certified Rigger-Theatre
Central Lighting & Equipment, Inc., Des Moines, Iowa, Central Lighting & Equipment


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## Reynolds (Feb 23, 2010)

It does, I talked with our Stage Manager and our drama teacher today, we're trying to arrange a day for an inspection.

Thanks again for your help.


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