Theatre Design & Technology - Spring 1992 - 49

Wire
Rope
Termination
JAY

G LERUM

he enrenainmenr indusrry
commonly uses wire rope
for rigging ro arrach barrens ro arbors, scenery ro
barrens and for orher
applicarions rhar suppon loads over rhe
heads of people. Oerermining rhe breaking srrengrh of differenr sizes of wire rope
in order ro selecr rhe acceprable safery or
design facror is relarively simple. Properly
rerminaring rhe wire rope is more complex. The wire rope is only as srrong as
rhe rerminarion.
The fWO devices mosr frequendy used
ro rerminare wire rope up ro 1/4" in
diamerer are cable clips and hand swaged
firrings. (Swaging wire rope over 1/4"0 is
usually done wirh a hydraulic press.) The
selecrion of rhe correcr device and careful
applicarion according ro manufacrurers'
insrrucrions are viral ro achieve a precise
rerminarion rhar meers rhe load requiremenrs.

DETERMINING
THE BREAKING
STRENGTH OF
WIRE ROPE IS
RELATIVELY
SIMPLE.
PROPERLY

CABLE CLIPS
In order ro assure consisrenr
qualiry, only clips manufacrured under Federal Specificarion FF-C-450 should be
used. Type I is mosr commonly used in rhe enrenainmem indusrry. This is rhe
common single grip, single
saddle, wirh U-bolrs and
nurs rype.

TERMINATING IT
When properly applied to
the wire rope, the clips wiLL
produce a termination equal
COMPLEX.
to 80% of the breaking
strength ofthe wire rope. The
saddles for Type I clips are
made from rwo differenr marerials: fOrged
stee!, a Type I Class 1 clip; and malleable
iron, a Type I Class 2 clip. Careful examinarion of rhe saddles shows rhe difference
(Figure 1). The forged saddle on rhe
righr has a smorher surface and usually
has a ridge where rhe fWO halves of rhe
forging die meer. The malleable saddle

IS MORE

on rhe lefr has rhe mold marks from
being sand casr and a slighrly pirred
appearance. Forged clips meering rhe
specificarion use heavy hex nurs; malleable clips use srandard hex nurs.
Four US clip manufacruring companies-Crosby, Chicago Hardware, Brewer-Tirchener, and Columbus McKinnon-were conracred for informarion
abour rheir producrs. All four of rhe
companies sell borh forged and malleable
clips. All fOur ofthe manujtzcturers recommend using only fOlged clips fOr load-bearing applications. All rhe forged clips from
rhese companies meer rhe federal specificarion and documemarion is available
from me manufacrurers ro cenifY rhis. In
addirion, Crosby and Brewer-Tirchener
sram p rhei r eli ps wi rh iden rificarion
codes rhar indicare rhe year of manufacrlife and rhe hear number of rhe meral
used for rhe saddle. Chemical analysis
records of each hear number are available
upon requesr.
Two of rhe companies, Chicago
Hardware and Brewer-Tirchener, sell
malleable clips rhar meer Federal Specificarion FF-C-450.None ofthe companies
recommend using maLLeable clips fOr the
entertainment industry. In facr, rheir lirerarure specifically srares rhar malleable
clips should only be used for lighr-dury,
non-load-bearing applicarions.
The main reason for nor using malleable clips for load-bearing applicarions
relares ro rhe manufacruring process.
Because rhe saddles are casr, rhey can
have inrernal flaws rhar are nor evidenr ro
rhe naked eye. Usually failure occurs ar
rhe rime rhe clips are righrened. Because
rhe saddle is malleable (rhar is, bendable),
a disronion caused by a weakness may go
unnoriced. A shock load can cause rhe
weakened clip ro fail. Samples of malleable clips obrained from rhe four manufacrurers show a consisrenr high qualiry
of producr.
However, rhis consisrenr high qualiry
is nor evidenr in off-brand clips rypically
found in hardware and orher srores rhar
do nor specialize in wire rope and firTD&T

1992 SPRING

Table of Contents for the Digital Edition of Theatre Design & Technology - Spring 1992