IBM Selectric Reference Manual

the negaf'ive four and negative five rotate positions to be
reduced, or the detenting ofthe negative five to be posi-
tive with respect to all the other rotate positions.
Since the ratio change adjustment will not affect the
negative five position, the typehead is then rehomed
to the negative five position making it detent properly
but causing all of the other positions (-4 through +5) to
detent too far negative. The lost motion of the rotate
arm is still felt between the negative four and negative
five rotat'e positions. The rotate arm motion in this area
can be controlled by the ratio change adjustment which
will be discussed under the next adjustment. This re-
homing of the typehead to the negative five position
(which is usually a slight refinement of the original
homing adjustment) is accomplished by the eccentric
stud ad justment rather than by sl ipping the rotate shaft
within the rotate pulley. It has been found that the
homing adjustment can readily be refined to the nega-
tive five, position with the eccentric stud while at the
same time obtaining a relaxed condition for the com-
pensator roller (accompl ished by control I ing the length
of the rotate I ink and reseating the compensator roller).
12. Ratio Change Adjustment - With the machine half-cycled
under power to an upper case -3 character, form the pad-
dle on the rotate eccentric arm until, the upper case -3
character detents the same as the upper case -5 char-
acter. Each time the paddle (Fig. 128) is formed the
machine must be recycled under power before observing
the detenting of the -3 character. This allows the ec-
centric shoulder to reseat itself in the compensating arm.
FI GURE 128. Arm Assembly. In -3 Position
CAUTION: When forming the paddle the V-shaped
wedging slot may accidentally open up causing the rol,ler
to drop. If this occurs, reseat the roller by raising it to
the top and striking a series of -5 characters. Thisad-,
justment should require only slight forming of the paddle.
2-39
Forming the paddle has no effect on the negative five
position. This can be easily seen by looking at Figure
129which shows the arm assembly in a negative five posi-
tion. In this position there is a large clearance between
the paddle and the barrel on the rotate arm therefore any
change in the paddle position just increases or decreas~s
this clearance without affecting the negative five posi-
tion of the rotate arm.
FI GURE 129. Arm Assembly in -5 Position
The paddle ad justment does affect all of the rotate posi--
tions from a negative three to a positive five position
equally because it controls how long the compensatinq
arm wi
II rotate about the eccentri c shou I der on the rotate
eccentric arm as ittravelsfrom the negative five position
towards
the negative three position. In other words the
more clearance there is between the rotate arm and the
paddle, the farther the compensating arm can travel un-
der a ratio change condition as it moves towards the
negative three position.
Figure 130illustrates how the detenting pattern of the
typehead is affected by the ratio change adjustment.
Notice in Figure 130A that all the rotate positions from
the -3 to the +5 detent equally but much less negative
than the -5. This indicates that there is too much ratio
change (too much motion) in the system between the -5
and the -3. The paddle should be formed in until the
-3 detents the same as the -5.
Figure 130B illustrates the detenting pattern of a system
that lacks a sufficient amount of ratio change. All the
rotate positions from -3 to +5 detent alike but too far
negative with respect to the -5. The system lacks motion
between the -5 and the -3 therefore the paddle should
be formed out to increase the amount of ratio chanqe.
Note that the negative four position is detenting the
same as the -3 In Figure 130B. This is because the ratio

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