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the pusher worked and the buffer merely moved forward with
it without performing any service. When the cam reaches 90
0 ,
or its first high point, the toggle springs are carried over center
by the momentum of the basket mechanism and the upper pin
leaves the pusher. The toggle springs reverse their direction
of tension and now power the operation. The toggle levers
assembly continues to rotate and the lower pin contacts the
lower wing of the buffer (Fig. 45). Buffer restoration is limit-
ed by the receding surface of the cam which is serrated and
sti II engaged with the power roll. The toggle springs, there-
fore, are not a Ilowed to s lam the seglTlent support into lower
case, but can only complete the operation as fast as the cam
will allow the buffer to restore. When the washer and motion
adiusting nuts on the stop screws strike the stop bracket, ro-
tation of the toggle levers ceases and the buffer leaves the
lower pin. The stud on the back of the buffer is cammed up-
ward by the bottom of the cutout in the toggle lever plate until
the buffer hairpin spring is over center. The buffer spring then
continues to raise the buffer unti I the buffer spring stud contacts
the upper edge of the window in the retainer (Fig. 44). The
buffer is now positioned to work on the upper pin in the next
shift operation. The tension of the toggle springs now holds
the mechanism in the upper case position. The key levers are
sti II he Id down or locked down by the shi ft lock. The cam has
rotated 180
°
and the inner I ug on the cam is aga i nst the cam
release lever lug (Fig. 46).
When the key lever is released and restores upward, the bot-
tom arm of the pusher is dropped behind the lower pin on the
toggle lever plate. The lug on the cam release lever moves
out of the path of the inner cam lug and the cam is released on
the power roll. The release lever then moves into the path of
the outer cam lug, to prevent a
~'epeat
operation. The cam
moves the pusher forward and the lower arm on the pusher con-
tacts the lower pin in the plate. This causes the toggle lever '
assembly to rotate clockwise and move the segment support up-
ward. The toggle springs power the mechanism after the cam
has reached 270°, its second high point, and the buffer works
on the upper· pin to cushion the basket mechanism. The pin on
the back of the buffer is cammed downward by the top of the
cutout in the toggle lever plate as the buffer completes its
restoration. The cutout and the buffer spring position the buf-
fer in I ine with the lower pin before the next operation is
begun.
Direction of
Cam Rotation
-
Outer Cam Lug
Figure 46.
Shift
Cam
23
The distance the segment support travels, either up or down
during shift, is called shift motion. This distance corresponds
to the distance between the bottom of the upper and lower
case characters. The maiority of IBM type styles have a
motion of .265", however, a few of the larger type styles have
a motion of .300".
TABULATION
The tab mechanism permits the operator to place typing in
previously determined accurate columns at a minimum of two
spaces between columns. A rack of tab stops, mounted on the
carriage and corresponding to the pitch of the typewriter,
allows the operator to select the positions where the carriage
will stop when the tab mechanism is activated. The operator
may then place typing in straight columns by tabulating to the
same stop when ever it is necessary to place figures in that
column. Tab stops may be set or cleared by depressing the
appropriate button located on the front cover at the right and
slightly above the keyboard. Through linkage, these buttons
operate set and clear levers attached to the rear frame of the
typewriter (Fig. 47). Spring fingers in the tab rack hold the
stops in either position. All set tab stops can be' cleared in
one operation by holding down the clear button and operating
the carriage return simultaneously. The tab rack does not
contain stops within a few spaces of either margin as tabulation
in these areas is infrequent. Additional stops may be installed
if the customer so desires.
Tab Lever shown operoted
II I
I
Figure 47. Tab Set and Clear Levers
The basic part of the tab mechanism is the tab lever assembly
consisting of the tab lever, tab check lever, margin control
lever, tab latch, extension, leaf spring and pawl release hook
(Fig. 48). It is mounted to a shock-absorbing horseshoe shaped
bracket on the left side of the rear rail by means of a pivot
stud. The tab lever can rotate freely about the pivot stud.
(Operation)
Depressing the tab key releases a double lobe single action
cam. As the cam is rotated by the power ro II, the cam frame
pulls the operating link and the top of the tab actuating lever
toward the front of the machine (Fig. 48). The actuating
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