Selectric Resources

 

DEAD KEY OPERATIONAL THEORY

 

The purpose of the dead key mechanism is to inhibit escapement on certain keyboard positions. This mechanism is used with several foreign keyboards. We will refer to the Trilingual keyboard for discussion purposes (Figure 1).

 

On the Trilingual keyboard the characters in positions 41 and 42 are accent marks used with the vowels in certain words to indicate pronunciation. These are “dead key”d characters and when they are typed, the carrier does not escape. The next character typed will appear directly below the accent mark.

Figure 1 — 74 Trilingual Keyboard

 

In order to inhibit escapement a 7th selection bail is installed in the keyboard. With the typewriter on its back, the dead key bail is the bottom bail. The interposer for a dead key position has an extra lug to operate this bail. Attached to the bail is a finger over which the eye of a cable is located. This cable is very similar to the cable used to control impression. The cover of the cable is held tight by two clamps, one for each end, mounted to the power frame. The rear end of the cable is attached to a hole in the bottom of the escapement trigger (Figure 2).

Figure 2 — Dead Key Mechanism

 

When an interposer in a dead key position is driven forward by the filter shaft, the rear lug on the interposer pulls the dead key bail forward. The finger on the dead key bail pulls the dead key cable which pivots the escapement trigger away from the lug on the escapement torque bar. A spring window which normally rests on the top of the escapement trigger is allowed to move in front of the escapement trigger as the trigger pivots. This prevents the trigger from restoring over the torque bar lug until the end of the print cycle. When the escapement mechanism operates, the trigger is away from the torque bar lug, which prevents escapement (Figure 3).

Figure 3 — Spring Window Operation

 

As the escapement trigger is pulled down, it moves out of contact with the spring window and is pulled forward by a spring. As the escapement mechanism restores, the top of the trigger contacts the bottom of the spring window, pushes it up and is allowed to restore in its normal position over the escapement torque bar lug.