IBM Selectric I/O Manual Of Instruction page 41

play; side play in the tilt detent; vertical play in the rear
carrier shoe; ti It ring side play; loose typehead latch; improp-
er detent timing; or worn rocker shaft bearings. Any of these
conditions can cause poor vertical alignment.
Rotate Alignment
Since the rotate mechanism must position the typehead to
eleven positions, it is a great deal more complex than the
ti It mechanism. The alignment concepts brought out under
the ti It mechanism also apply to the rotate mechanism irre-
gardless of its complexity. Like the ti It ring, the typehead
is also detented after it has been coarse aligned to approxi-
mately the correct position (which is within the allowable
band width). Bui It-in play of the typehead allows the rotate
detent to refine the selected type head position after the head
has been coarse aligned. This play comes from backlash be-
tween the slots in the ball joint and the pins in the upper and
lower ball sockets. The rotate detent mounts on the ti It ring
and operates in V-shaped notches cut into the skirt of the
typehead (Fig. 87). It is spring loaded at the rear into en-
gagement with the typehead.
FIGURE 87. Detent Mechanism
As in the tilt mechanism, once the rotate detent has fully
seated in the typehead notch any horizontal misalignment
problems cannot be attributed to coarse alignment adjustments.
The problem lies in the carrier and rocker area and usually is
caused by one of the following: side play in the rotate de-
tent; improper detent timing; excessive side play of the rock-
er; binds in the rear carrier shoe; or anything that will re-
strict the carrier from escaping properly.
Detenting
The typehead cannot be ti Ited or rotated with the detents en-
gaged. They must be he Id out of engagement unti I the type-
head has been completely positioned. They must also be re-
moved from engagement before the typehead can be restored
to rest position. The rotate detent operates against the tilt
detent. As long as the tilt detent is not allowed to rise, the
32
rotate detent cannot enter the notches of the typehead. The
ti It detent is controlled by a small lever called the detent
actuating lever located under the left side of the yoke (Fig.
87). The lever pivots at the rear and extends forward along
the right side of a lower extension of the ti It detent. When
the detent actuating lever is operated to the left, the ti It de-
tent moves down pushing the rotate detent down with it.
When the actuating lever moves to the right, both detents
are a II owed to ri se •
Movement of the detent actuating lever is controlled by the
detent cam through the detent cam follower (Fig. 87). The
cam follower i!> pivoted on a bracket below and to the rear of
the print sleeve and extends up alongside the detent cam in
position to operate the detent actuating lever. The camming
surface of the detent cam is on the left side so that operation
of the cam follower is toward the left against the detent act-
uating lever.
The rotate detent does not pivot into engagemen t as the ti It
detent does. It contains an elongated hole at the front which
allows both the front and rear of the detent to move up and
down (Fig. 88). A small flat link at the top stabi lizes the
detent. If the rotate detent were pivoted at the front, the
amount of travel and timing of the detent would vary with
the tilt selection. With the sliding arrangement, the rotate
detent action is approximately the same for all tilt selec-
tions.
Active Position
Detent Link
Rest
Position~·
FIGURE 88. Rotate Detent
While the typehead is being positioned, the cam follower is
against the high part of the detent cam. This causes the de-
tent actuating lever to be held to the left to prevent the de-
tents from engaging their notches. During the positioning of
the typehead, the detent cam is rotating, but it maintains
the same high point for the cam follower. As soon as the
rotate and ti It operati ons have been completed, the cam fol-
lower is allowed to move to the right into a recess in the de-
tent cam. This allows the detent actuating lever to move to
the right to permit operation of the tilt and rotate detents.
As the typehead is being moved toward the platen the detent
cam continues to turn, but it maintains the same low point
for
the follower.
As soon as the character has printed, locking the typehead in
positi on is no longer necessary; therefore the detents can be
disengaged to a II ow the typehead to restore to the rest posi-
tion. As the rocker is restoring to the rest position, the de-
tent cam moves the cam follower back to the left onto the
high part of the cam. This action causes the detent actuating
lever to disengage the detents from their notches. Timing of
the detenting is such that both detents begin to engage their
notches just as the type head completes its positioning and are
disengaged just as the type head starts to rotate and/or tilt
bacl< to the rest positi on.