IBM Selectric Reference Manual

Print Cam Follower
FIGURE 138. Velocity Control Plate Adjustment
the rear increases the powered travel, as shown by dimen-
sion B.
Because
of the constant operational speed of the print
cam
and follower, the type head velocity must increase
or decrease proportional to the increase or decrease in
powered travel. An accompanying change in typehead
velocity occurs when the powered travel is changed be-
cause the type head must a I ways t rave I from its rest pos i -
tion to its active position in the same amount of time
regardless of what this distance may be.
The proper impact velocity of the typehead can be
achievedbycontrollingthe amount of powered travel of
the typehead while maintaining at the same time the
correct amount of free flight. Since the position of the
platen has been previously fixed and the amount of free
flight is determined by the point at which the limit of
powered travel occurs relative to the platen, only the
rest position (beginning of powered travel) may change
when the amount of powered travel is Ghanged. There-
fore, in order to maintain a fixed amount of free flight
to the typehead when the amount of powered travel is
changed, the velocity control plate pin must also be ad-
justed up or down relative to the rocker.
The eccentric shouldered nut (Fig. 139) on the velocity
Type Head
Held Slightly~
Forward
Slight Drag On Three Tab Cards
Approx. 1/32" Of Slot Visible
Above Head Of Screw
FIGURE 139. Velocity Control Plate Eccentric Adjustment
2-44
control plate provides a means of control I ing the vertical
position of the velocity control plate pin relative to the
rockerthereby controll ing the free fl i ght of the typehead.
The elongated hole in the ~elocity control plate (behind
the binding screw) allows the velocity control plate pin
to be adjusted front or rear in the forked slot of the fol-
lower thereby controlling the amount of powered travel
that the typehead will receive. Each adjustment affects
the otherand must be adjusted alternately until both are
correct .
The
adjustments can be made easily if the following pro-
cedure is used.
a. Raise the anvil adjusting eccentrics and the restor-
ing cam follower eccentric to prevent any inter-
ference, and remove the ribbon feed plate for ac-
cessibility.
b. If the velocity control plate is loose or completely
out of adjustment, set the high part of the eccentric
forward and tighten it in place. Adjust the plate so
that about 1/32" ofthe adjusting slot is visible above
the binding screw and tighten the screw friction
tight. These settings provide a good starting point.
c. Hand cycle the machine using a zero rotate, zero
ti It character until the print cam follower is on the
high point of the cam. Do not hold the typehead
toward the platen. With the mechanism in this posi-
tion, adjust the velocity control plate eccentric un-
til a slight drag is felt on three tab cards inserted
between the typehead and the platen (Fig. 139). A
heavy drag should be felt on four cards. No drag
should be felt on two cards. You should not be able
to insert five cards.
This will place the limit of powered travel of the
typehead .020" to .030" away from the platen
(providing the typehead with the proper amount of
free flight).
Loosen This Screw
FIGURE 140. Velocity Control Plate Adjustment

IBM Selectric Specifications

General

Type	Electric typewriter
Introduced	1961
Keyboard Layout	QWERTY
Carriage Return	Electric
Manufacturer	IBM
Printing Technology	Typeball (golf ball)
Power Source	AC Power
Power Supply	120V AC