IBM Selectric - Tabulator Mechanism

2.
3.
4.
1.
CAUTION: Be sure that the tab set and clear lever is
fully seated on top of the two pivot pins on the left side
of the powerframe.
Tab Set and Clear Link - Adjustthelinksothatthe slope
of the keybutton matches the slope of the ON/OFF
switch keybutton with the switch in the OFF position.
NOTE: A I ink guide found on the 721 should be adjust-
ed so that it will permit free operation without allowing
the I ink to flex during a set or clear operation. The link
guide must also be positioned in the slot of the selector
latch bai I shaft to maintain the proper lateral position
of the shaft.
Set and C lear Arm Stops - Form the stop I ugs on the set
andclear lever bracket (Fig. 161) so that they limit the
movement of the arm just as the tab stop fully reaches its
set or cleared position. Also, form the extension on the
rear stop lug so the tab set and clear arm cannot pivot
sideways out of engagement with the tab rack bellcrank.
Set And C lear Lever
Bracket
Set And C lear Arm
FIGURE 161. Set And Clear Arm Stops
NOTE: On the early style tab set and clear mechanism
the stop lugs were anchored and adjusted by two screws
on the outside of the powerframe.
Tab Rack Brake - Ad just the tab rack brake so that the
tabrackwill not flip past the rest position when released
from either a set or clear position. The tab rack must
return fully to the rest position when the keybutton is
released slowly. The brake is located just inside the
powerframe at the left end of the tab rack.
TABULATOR MECHANISM
Tab Lever Stop - Form the stop on the escapement bracket
(Fig. 162) to obtain .00111 to .003
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clearance between
the verticallugon the tab lever and the backspace pawl
when the tab lever is at rest and the backspace pawl is
fully seated in its rack.
55
This small clearance insuresthat the backspace pawl will
be allowed to bottom in its rack and that a minimum
amount of tab lever motion wil! be required to remove
both the backspace and escapement pawls from their racks
during a tabulation operation.
Tab Lever Stop
--
Tab Lever ~ ..... ~-.!-
Backspace Pawl ~
.00111 to .003
11
FIG URE 162. Tab Lever Stop
2. Tab Lever Pawl - Ad just the pawl forward or back on the
tab lever so that the tip of the pawl clears a SET tab
stop by .035
n
to .04Y with the tab lever at rest (Fi g.
163) .
3.
Tab Lever
t
Tab Rack
---~J,
---:TTn=:t[. :' .:-: ,.1 I-~
I •
.. . ~
•. ~ .035" To .045"
I)/_c~ Ad ius! Tob Lever
I -W- Pawl
FIG URE 163. Tab Lever Pawl
The ad justment ofthe tab lever pawl has an effect on the
amount of overlap between the tab stop and the pawl ti p
in the active position. It also directly affects the pawl
clearance during tabulation. Unless the tab lever pawl
is properly adjusted, correct pawl clearance cannot be
obtained.
The ad j ustment of the tab iever pawl can be measured by
using the push-end of the large spring hook. The push-
end is approximatel y .035
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th i ck.
Pawl Clearance - The upright lug of the tab latch should
be formed forward or back so that the tip of the escape-
ment pawl clears the escapement rack teeth by .005" to
. 01 0" when the tab lever is latched to the rear.
The ad justment insures that the escapement pawl wi II re-
enter the rack quickly to minimize the 'Chances of en-
tering the wrong rack tooth. If excessive clearance is
present, it is also possible that the tab keylever and as-
sociated parts might not have enough throw to positively
latch the tab lever each time.