IBM Selectric - Page 70

Tangent
Supply Drag Lever
FIGURE 199. Pressure Roller Release Arm
Shock Spring
Feed Plate ........ ___ ,/
FIGURE 200.
Shock and Drag Spring Adjustments
69
RIBBON TRACKING ADJUSTMENTS
The term
IItracking II is used in this mechanism to describe the
path or course that the ri bbon assumes as it prog resses from the
supply spool through the guides and onto the take-up spool.
The mechanism contains a series of guides and springs which
are designed to establish and maintain a constant ribbon track-
ing characteristic throughout the ribbon circuit. Since the en-
tire mechanism issubject to vibrations, the purpose for some of
the adjustments is to over-ride the effects that these vibrations
incur on the ribbon feed operation. The tracking adjustments
are inter-related and must be considered together in order to
obtain reliable ribbon trackin?:
1. Sup)ly Spool Drag Spring - Position the drag spring par-
aile tothe front edge of the feed plate (Fig. 200). Mov-
ing the spring further away from the center of the supply
spool increases the amount of drag, while bringing it
closer will decrease the amount of drag.
NOTE: Use the following technique to check and ad-
just the tension of the drag spring: Remove the C-clip
which retains the supply spool on its pivot stud. Then,
raise the spool slightlyand allow it tosettle down onto the
drag spring by its own weight. If the drag springs tension
is properly adjusted it wi II hold the supply spool elevated
so that 1/2 of the ang led surface (chamfer) on the top of
the pivot stud is protruding above the top face of the
spool (Fig. 201). Form the drag spring up or down to ob-
tain this condition.
Supply Spool Pivot Stud
Supply Spool
Feed Plate Supply Spool Drag Spring
FIGURE 201. Supply Spool Drag Spring Check
CAUTION: The drag that is supplied to the core of the
ribbon supply by this drag spring during a ribbon feed op-
eration is necessary in order to maintain a tightly wrapped
spool ofribbon on the supply spool. If a condition exists
where the outer wraps of ribbon on the supply spool have
become loose check the suppl y spool brake adj ustment
first
before suspecting the drag spring.
Excessive drag on the supply spool may cQuse ribbon slip-
page at the feed and pressure rollers which could result
in characters overlapping on the ribbon. Character
overlap from excessive drag is most apparent when nearing
theendof a spool of ribbon on the supply spool. This is