IBM Selectric - Page 73

7.
Take-Up Tensi on - The recommended method of con-
troll i ng the amount of take-up tensi on to the take-up
spool is by the installation of either a light, medium,
or heavy drive spring. These springs are color coded
as follows:
Light .
Medium
Heavy. .
red
no color
blue
CAUTI ON: Do not attempt to control the amount of
take-up tensi o~either stretching the drive spring or
cutti ng loops off one end of the spri ng. Thi s method is
not effective and will only lead to erratic take-up ten-
sion.
SERVICE HINT: A lack of sufficient take-up tension
can usually be recognized by the fact that the take-up
spool either fails to hold an enti re spool of ribbon caus-
ing spi lIage; or, upon reaching the end of a spool of rib-
bon the take-up spool is filled beyond its safe capacity
which is approximately 1/32" within the outer edge of
the flanges. If this condition exists, before a decision
is made to replace the drive spring both the spring and
its pulleys should be thoroughly cleaned with cleaning
fluid and then lubricated I ightly with ET oi I. If cleaning
and oiling does not bring about the desired results a new
drive spring of the same category shou Id be tried first be-
fore going to a heavier drive spring.
Excessive take-up tension will generally cause the rib-
bon to be pu lied through the feed and pressure rollers
resulting in over feeding of the ribbon. This condition
is most apparent at the beginning of a new supply of
ribbon when the take-up tensi on fe It at the feed and
pressure rollers is the greatest. If there is enough rib-
bon slippage a noticeable reduction in character yield
perspoolof ribbon will be present. In addition, exces-
sive take-up tension can be a contributing factor to an
overly sensitive tracking condition.
(Screw)
Ribbon hangs slack
Erratic take-up tension is generally caused by either a
dirtyordamageddrive spring. It can usually be detect-
ed by examining the feeding pattern on the ribbon. If
there are signs of both over-feeding and character over-
lap together on the ribbon this is a good indication that
erratic take-up tension is present. The drive and take-
uppulleys should be cleaned and a new drive spring in-
stalled(lubricated lightly with ET oil). Erratic take-up
may also contribute to unreliable tracking.
NOTE: If at some time it becomes necessary to check
the amount of take-up tensi on, it may be measured with
a gram gauge (I isted under Tools and Suppl i es) usi ng the
following procedure:
a. Thread a small machine screw, approximately 1/2"
long, up through the hole in the bottom flange of
the transparent take-upspool. (This hole, provided
for this purpose, is located exactly one inch from
the center of the spool.)
b. Withthetake-upspool installed, remove the ribbon
from between the feed and pressure rollers and let
it hang slack.
c. Remove the type head, disconnect the escapement
trip link, and position the carrier at the left hand
margin.
d. Place the gram gage (using a times one spring blade)
as shown in Figure 207 and operate the repeat under-
score. For the most accurate reading try to keep
the end of the spring blade in line with the center
of the spool. Also, keep the small hole in the end
of the blade against the machine screw as shown by
the insert in Figure 207. If the measurement ob-
tained fa 115 within a range of 45 to 55 grams the
take-up tensi on is correct.
Gram Gauge
FIGURE 207.
Take-Up Tension Check
72