IBM Selectric I/O Manual Of Instruction page 89

Margin Stops
The margin stops are mounted on the margin rack. The rack
is positioned horizontally in the machine in front of the car-
rier. Each margin stop has a slider and pin assembly that
meshes with teeth at the rear of the margin rack (Fig. 177).
The number of teeth per inch in the margin rack corresponds
to the pitch of the machine.
Margin Set Lever
SI ider and Pin
Margin Stop Latch
Line Lock Bracket
FIGURE 177. Left Margin Mechanism
Each margin stop has a margin set lever attached to the slider
and pin assembly. The margin set levers extend through a
slot in the front case so as to be accessible to the operator.
Either margin stop may be repositioned by pushing the margin
set lever to the rear to disengage the pin from the rack and
then by sliding the margin stop along the rack to the desired
location. A scribe line on the margin set lever acts as a
pointer to indicate the position of the margin stop in relation
to the sca Ie on the front of the case. A pointer on the front
of the carrier indicates the position of the carrier.
Keyboard Lock Interposer
Keyboard Lock
Bell crank
The left hand margin stop controls the left margin on the pa-
per. An extension of the stop is struck by the margin stop
latch pivoted on a bracket attached to the carrier (Fig. 177).
This action forces the margin rack to the left to unlatch the
carrier return leaving the carrier resting at the left margin
position.
Line Lock - (Early)
The purpose of the line lock mechanism is to
loc~
the key-
board when the carrier has reached the right hand margin on
the paper. With the keyboard locked, the operator cannot in-
advertently continue typing at that position.
The line lock mechanism is operated by the right hand margin
stop. In addition to operating the line lock, the margin stop
also rings a bell several spaces before the line lock action oc-
curs. The bell warns the typist that the carrier is near the
margin stop. In most cases this allows sufficient space to com-
plete a word or phrase before the line lock occurs. The typist
can then return the carrier to begin the next line.
If the typist continues typing after the bell rings, the key-
board is locked after a few spaces to prevent typing on the
margin. The keyboard is locked by forcing a special bell-
crank into the selector compensator (Fig. 178). The keyboard
lock bellcrank forces the steel balls of the compensator to
shift in the tube and block the depression of any other inter-
poser.
The keyboard lock bellcrank is actuated indirectly by an arm
welded to the bellringer bai I near the left end. A camming
surface on the front of the line lock bracket forces the bai I to
pivot farther forward after ringing the bel I (Fig. 179). The
arm welded to the bai I moves downward forcing down on the
keyboard lock interposer. The keyboard lock interposer and
the keyboard lock bellcrank pivot on the character interposer
fulcrum rod. The keyboard lock interposer and bellcrank are
connected at the rear by an extension spring. When the in-
terposer is forced down, the extension spring pulls the bell-
crank down into the selector compensator.
Because of the machine's character storage feature and the
speed with which the interposers can be depressed, it is not
\"'~----I
i ne Lock Bracket
FIGURE 178. Line Lock Mechanism - {Early Style}
70