Selectric Resources

ESCAPEMENT (RB/S) OPERATIONAL THEORY

The rotary backspace (RB/S) escapement mechanism  uses a gear on the carrier return cord drum that receives motion from a driver to move the carrier during a backspace operation. The vertical position of the escapement pawl is critical in machines with rotary backspace. The pawl must be centered in the escapement rack within the opening in the escapement rail. An escapement pawl guide bracket is mounted above the escapement pawl. The escapement pawl guide lug extends down from the bracket and is formed under the escapement pawl to control vertical movement. The escapement pawl vertical position is controlled by the vertical position of the carrier, which is adjustable. This is done by an elongated mounting slot in the rear carrier shoe. As the carrier shoe is adjusted left or right, the rear of the carrier is raised or lowered (Figure 1)

RB/S escapement functions in the same way as NRB/S escapement. The only differences are the escapement rack (covered in the Switch Pitch Section), the escapement pawl, the escapement pawl mounting and some adjustments.

RB/S machines use a steel cable in place of the nylon carrier return cord. Early level dual pitch machines use a steel cable for both the carrier return cord and the escapement cord.

Figure 1 — Escapement Mechanism