IBM Selectric I/O Manual Of Instruction page 47

Several factors affect detent timing. Some of the most im-
portant are: the adjustments of the rotate and ti It systems,
typehead homing, detent actuating lever and cam adjustments,
and timing of the print shaft relative to the cycle shaft. If
any of these are changed, the machine MUST ALWAYS be
cycled by hand to check the detenting action before it is
operated under power.
It should be noted that the detents are spring loaded into en-
gagement, but they are driven out of engagement by the cam.
This is to prevent parts breakage shou Id the typehead not be
properly positioned when the detents try to engage.
Head Play
Figure 97 illustrates typehead play by showing a single de-
tent notch (of the typehead). This built in play should be
approximately .045".
Head Play
Removed In
The Negative
Direction
Band Width
FIGURE
97.
Head Play
Removed In
The Positive
Direction
~
"Head Play"
approximately .045"
Typehead Play
Band width is defined as the difference in detenting between
the rotate se lecti on that detents the least negative and the
rotate se lection that detents the most negative with respect to
the rotate detent. The head play must be removed in a
clockwise (negative) direction when the comparison is made
(Fig. 98).
The typing element is "homed" to the rotate selection that
wi II coarse a lign the most positive (with respect to the rotate
detent) when the head play is removed in the negative di-
rection. It is IIhomed" so that this rotate selection will de-
tent
.010"
to
.020"
on the negative side of the detent notch
when the head play is removed in the negative direction
(Fig. 99) •
38
Head Play
Removed In
The Negative
Direction
Head Play
~
Removed In
The Negative
Direction
~ ~
Band Width
I
Rotate Selection
That Detents The
Least Negative
With Respect To
The Detent
Rotate Selection
That Detents The
Most Negative
With Respect
To The Detent
FIGURE 98. Band Width
Head
Play~
Removed In
The Negative
Direction
.010"
To
.020"
Of The Head
~
r-Play Utilized For Detent
~-t-+-_
Timing Purposes
I
I
I I
I I
----+1
I
FIGURE
99.
The Positive
Direction
t+-"Head Play"
Typehead Homing
The purpose of this adjustment is to slightly retard the restor-
ing of the typehead whenever it restores in the positive di-
rection so that the rotate detent can begin to withdraw be-
fore the typehead starts to restore. If the wi thdrawa I of the
detent did not lead the restoring of the typehead, the detent
would restrict the head from restoring causing breakage in
the system. This homing adjustment uses up approximately
1/4 of the typehead play.