The rope lock
or lock dog is the part of a theatrical stage rigging
system that secures the arbor
. Each lineset
on a counterweight fly system
has a rope lock mounted to the pin rail
. The purchase line
passes through the rope lock. When the handle on the rope lock is pushed into the fully vertical position it clamps the purchase line thus preventing any movement in the system. Usually, the purchase line passes through a small steel ring which can be hooked over the rope lock securing it in the "up" position.
When the locking ring is removed and the handle on the rope lock lowered, the purchase line can again be used to control the lineset.
Always use caution when removing the rope lock. If for some reason the system was left out of weight (unbalanced), removing the rope lock will cause either the batten or the arbor to coming crashing to the ground. Always inspect the purchase line to see if there appears to be too much tension on the rope. This is a good sign that the system is out of weight. Stop, and call for assistance.
An out of control lineset is a dangerous thing. At best the ensuing crash will severely damage the sheaves. At worst, the batten and associated scenery can come crashing to the deck or be violently yanked to the grid. If this hasn't yet severely killed or injured someone, it is likely from this point that the 20 to 50 pound counterweights will jump the arbor falling directly where you are standing. After this the wire rope will fail causing the heavy steel batten to fall back to the floor.
Attempting to stop a runaway arbor is also not an option. It can leave you with extremely severe rope burn or yank your body up into the air until you smack into the grid, thus causing you to fall back to the floor again.
A fly system is a very dangerous thing to those not familiar with it. If you don't know what you are doing, whatever you do, Don't touch the rope lock!
Part of the Stage Rigging Metanode