Theatre Design & Technology - Winter 1980 - 10

The Inside Ladder
The use of 2" x 6" for the sub frame also made it possible to utilize
elements of a caster jack scheme devised earlier (see "Scenic Wagon
Restraint Systems," TD& T, Summer 1977). The principal alteration
involved operating all four caster jacks from a single winch shaft. This
was required by the limited space available but had the added benefit
of reducing jack operation to a one hand maneuver (Figs. 4, 5).
The ladder itself was constructed of 2" nominal thin-wall steel conduit with 3~" N.P.S. pipe rungs. The rungs were passed through holes
bored in the columns and brazed in position. This arrangment provided maximum frame rigidity and negligible difficulty with joint "fit
up" (Figs. 4, 6). The rung spacing was developed from a partial full
scale mock-up and seemed to provide the best combination of easy
climbing conditions, best access to various work heights and a comfortable hands free stance in typical work positions. Note that two
rungs are omitted at one side near the bottom to permit access to the
inside of the ladder (Fig. 2). The ladder was constructed in two parts,
the coupling being made by insert sleeves fastened with "Is" bolts (Fig.
6).

The boom pivot bearing is supported on back to back pairs of 1 %"

*''
*''

x 1 %" X
angle irons which were in turn bolted to the ladder legs
with "Is" bolts (Fig. 7). The unsupported angle iron flanges are stif-

Figure 1

The flexible facade system required a stagehand to work easily at
any height up to approximately 19' head level with both hands free,
and on a structure that would be stable and yet be easily moved while
being entirely self supporting in less than four square feet of stage
space. Furthermore, it was necessary to lift various components of
the facade into position since hanging pulleys from fixed portions of
the building structure had proved to be too cumbersome and time
consuming. Finally, the material cost had to be kept to less than about
$200.00.
The arrangement finally devised might be called an "inside ladder"
in that the operator climbs up inside a square column (Fig. 1). Since
the supporting base is wider than the column, the operator is physically restrained from ever placing his center of gravity beyond the
supports, so the arrangement is intrinsically stable in spite of its relatively small base. Maneuverability is provided by mounting this structure on lever-operated caster jacks (Figs. 2, 3, 4, 5). The self-contained lifting facility is provided by a rotating boom at the top of the
structure. By bringing the purchase line down the end of the boom opposite the load, no significant bending forces are exerted on the boom
pivot. Furthermore, provided the line operator at floor level stays fairly
close to the base, the lateral stability of the structure as a whole is not
compromised (Figs. 1, 2). Tie-off cleats are provided approximately 5'
above floor level as an additional convenience.
The base consists of two frames: a 2" x 6" nominal timber frame
covered with 'A" ply, on top of which is a second framework of 3"
channel iron. The latter acts essentially as outriggers for the ladder itself while the perimeter of 2" x 6" serves as a continuous pad to protect the stage floor and to spread the weight of the scaffold over as
much flooring as possible within the space available. The channel iron
frame is lag screwed to the wood base through 'A" X 5" bearing
plates. The long 'A" x 5" X 42" plates also serve to reinforce the
lower joints of the channel iron frame and provide a bearing surface
for the feet of the ladder (Fig. 3). The ladder feet are stabilized by
angle iron sockets and secured in position by "Is" bolts. The recess
formed by the channel iron frame also provides a convenient containment for the 400 Ibs. of stageweights used to stabilize the structure.

Theatre Design & Technology

fened by
plates. The 2" conduit boom pivot bearing was radially
stabilized in the angle iron assembly by 1 %" nom. bolt size washers
which were enlarged to approximately 2.2" 1.0. and welded to the
angle iron frame and conduit.
The boom consisted of a length of Binkley B-24 strut which was
brazed to a 1 %" N.B.S. washer which had in turn been welded to the
end of a piece of 1 %" N.P.S. pipe to serve as the pivot shaft. The assembly was held together with a length of 3~" threaded rod the upper
end of which was flattened and drilled to accept a shackle. This was
done to provide a convenient symmetrically loaded way of lifting the
upper ladder section into position during assembly. The sheave frame
design was adapted from another application. While generally satisfactory, experience has shown that it would have been better to cut
back the top of the frames at approximately 45° to reduce the possibility of fouling on curtains, etc., as the scaffold is moved about the
stage. This and a few other minor modifications are shown in the
drawings. Notice also that some features of this design were conditioned by available stock materials and other similar considerations.
For this reason the prospective builder is cautioned to verify for himself that the structure is sufficiently strong for the intended application.
Generally, this device has lived up to, and in some respects exceeded, design requirements especially in its remarkable stability.
Under test conditions with suitable safety precautions, a strong man
positioned at the highest possible working position in the ladder was
barely able to tip the structure by pulling on a stationary object. It has
been useful not only for its original purpose, but for more general applications.
lt should be reported, however, that several difficulties have surfaced since this unit was put into service about a year ago. Unquestionably the most serious of these is the difficulty of moving the unit
when jacked up on casters. The weight of the scaffold with its fairly
massive ballast plus that of the operator who often prefers to ride part
way in the ladder to save time, makes changing caster direction difficult in the relatively narrow spaces usually available on stage (Fig. 1).
The most obvious solution would be an air bearing but the necessary
high volume air supply is not readily available in the Brown County
Playhouse. Given the apparently large margin of stability, it is likely
we can safely remove a substantial amount of ballast. Another solution might be to replace the present rubber tired casters with a denser, less compressible material though the limitation here may be the
possibility of stage floor damage.
One other point that should be mentioned is the possibility of injury
from the jack handle. Although the force required at the operating end
is not great, if the handle is released suddenly it can be fairly dangerous. Thus, all those likely to operate the jack should be warned of
this potential danger.
Notwithstanding these limitations, however, the unique features of
the "inside ladder" have made it useful not only for its original purpose but as mentioned, for more general applications. lt is possible
that other builders not confronted with the special necessities of facade construction will devise ways to make this design more useful as
a general service appliance.
USITT/Winter, 1980

Table of Contents for the Digital Edition of Theatre Design & Technology - Winter 1980