Rob wrote:
> I'm working with a friend at a new facility. The architects want to
> install: "18' lighting pipes referred to as "pipe booms"...They are to
> be attached to the floor using a threaded flange and tied of using a
> heavy duty rope to a location above the stage"
>
> My concern and the concern of the lighting install company is:
> "...that the pipe is too long and has too much load for the specified
> flange attachment (5" floor flange). We recommend a larger floor base
> which will offer better stability for a pipe of that length and
> eliminate the chance of causing damage to the floor and also the
> possibility of a more rigid attachment point for the top of the pipe
> in addition to the rope tie off."
>
> The architects claim this is a 50 year old practice used in other
> sites. I think it sounds suspect-- it would not be my choice. Any
> comments?
Dear Rob,
It is a common practice but only where 2 1/2" to 3" long lag screws can
be driven into the deck through the four flange holes. The point of
doing a boom lag/flange arrangement is that the base isn't any bigger
than necessary to hold the boom down. The weight is ALL held up at the
top in the grid by safely and properly tied off lines that have been
very carefully spotted, either through sheaves and head blocks to the
pinrail, or tied off at their spot points in the grid. NOTE: Only well
maintained lines and professional flymen should be allowed to rig this.
Traditionally, whole booms - sidearms, instruments, twofers, cables and
breakouts - are built horizontally on the deck across sawhorses, with a
flange at the bottom and boom pickup line at the top, properly
half-hitched at the top and secured to the boom below the topmost
instrument's sidearm C-clamp with a clove hitch finished with one
half-hitch. Circuit cable is dressed up the pipe if being fed from
overhead drops or cable picks in the air. When ready to be flown, the
crew on the deck gives the boom a helping shove up as the grid crew [or
pinrail flymen] take the strain and pull the boom vertical until it
floats about a foot off the deck. The boom is allowed to stretch the
pickup line for a while so it gets as taut as possible under the full
weight of the assembled boom.
When it is time to actually 'spot' the boom to its floor mark, the most
secure procedure is to have the boom line let in very easy on its pin
until the flange is about two inches off the deck. The line is secured
with a 'good double tie' on the pin and then the deck crew waits until
the flyman gives the OK to lag. At that point, one stagehand with an
impact wrench drives each lag [with a washer on top of the flange hole]
into the deck while two other stagehands hold the boom steady at the
correct angle for the sidearms. They step on the flange, adding their
weight to the boom to stretch it the last two inches so it is truly
tight. The lags do the rest and hold it until load out. Once tied off,
the boomline is marked or tagged by the flyman as a line in use [under a
load] which the double tie should tell you anyway.
This method is as safe as a full 24"+ boom base, loaded with sandbags
and an overhead safety line. The advantage is that the small footprint
of a 5" flange allows spotting the boom very close to legs, set pieces,
and it never sticks out any further than any instrument on the boom
itself. For fine 'tuning' the boom, the 5" flange should have at least
one 180 degree thread spin of freeplay so any re-angling of the sidearms
can be done by simply twisting the whole boom one way or the other. If
the flange is on so tight that you cannot turn it after lagging, you've
boxed yourself in. When the LD/TD is happy with the whole position, a
right angle 'crowsfoot' should be attached to the base of the boompipe
above the flange by its C-clamp and its mini 3" flange drilled to the
deck with regular drywall or any short 1" screws.
Bad ASCII art:
Boom crowsfoot [standard sidearm parts]
| |
C-clamp======== <== 1/2" pipe 90 elbow
| | || <== 1/2" pipe
| | ||
| | ||
------------ ----<== 3" flange
When all is done, then tighten the C-clamp to lock in everything. The
advantage of a crowsfoot is that it can be angled in any direction off
the boom pipe and secured out of the way of performer's feet passing by.
The most used angle is directly under the instruments or on-off stage,
but the most im****tant position is the one that's out of the way.
Without having to fight the rigidity of a wide boom base on the floor,
breast lines can be used to straighten or correct a leaning boom from up
to down or offstage by tying the breastline off the boomline and pulling
it to the desired angle to offset and make a perfectly vertical boom.
This makes doing really tight shutter cuts manageable in close spaces.
As long as this method is correctly applied, the boom must be considered
a flown piece and treated as such. This means qualified personnel on the
flyfloor or grid. If the boom lines must be dead tied to the grid, then
you must have experienced hands who know how to properly tie off a line
under full load. Slipping is NOT an option.
In practice over the years, I have built many 20' - 24' booms with 10 to
12 instruments, double sidearms, loaded with color scrollers, strobes,
cables, foldback speakers from sound, and the whole thing flown, dead
tied, and just marrying the deck on a well lagged 5" flange - on one
single hemp line [when I began]; now, synthetic braided lines and wire
rope safeties everywhere.
Regards,
Bert
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