IBM Selectric I/O Manual Of Instruction page 39

The same method is used to eliminate alignment variations in
both the ti It and rotate mechanisms. Since the ti It mechanism
operates basically the same as the rotate mechanism and is
simpler in structure, most of the alignment concepts will 'be
discussed in the ti It mechanism. A good understanding of
these concepts is required in order to properly diagnose an
alignment problem.
Tilt Alignment
To insure that any character in one of the four bands of char-
acters on the typehead is properly aligned vertically when
the typehead prints, the tilt ring must be tilted to an exact
position and locked. As previously mentioned, the tilt ring
cannot be accu rately positi oned by its mechanism a lone be-
cause of uncontrollable factors. To overcome this conditi on,
the detent mechanism con refine and lock the tilt ring in the
exact position desired, after the tilt mechanism coarsely po-
siti ons the ti It ring. This is accomplished by placing a spec-
ific amount of play in the tilt ring and using a detenting
mechanism to refine and lock the ti It ring into position.
This bui It-in play is located in the ti It pulley link on the
gearless tilt and is commonly referred to as "tilt ring play".
On the old style ti It mechanism, the ti It ring play is felt as
backlash in the ti It ring sector gears. If the ti It mechanism
tends to supply too much or too little motion to the tilt ring
for a given tilt selection, the detenting mechanism will cor-
rect this error by utilizing the tilt ring play. The left side
of the ti It ring contains four V-shaped notches that corres-
pond to the four ti It positions. A small arm called the ti It
detent mounts in a s lot on the left si de of the yoke and oper-
ates in the notches on the ti
It
ring. When the ti It ring is
operated to approximately the correct tilt position, the tilt
detent is allowed to enter one of the notches in the ti It ring
(Fig.
81).
A heavy extension spring causes the detent to
seat in the V-shaped notch; thus camming the tilt ring into,
and locking it in an exact print position. It is the built-in
"ti It ring play" that enables the ti It detent to cam the ti It
ring into the proper tilt position.
Tilt Ring
Tilt Detent
FIGURE 81. Tilt Ring Detenting
Since the ti It detent assumes the responsibi lity of refining the
position of the tilt ring to the proper place, the requirement
of the tilt mechanism is only to coarse align the tilt ring (to
each ti It positi on when selected) so that the ti It detent can
enter and bottom in the correct notch without uti lizing all
the tilt ring play. This means that the largest coarse align-
ment variation between any two of the four ti It positions must
30
not exceed the ti It ring play, or a detenting fai lure wi II re-
sult. To insure that detenting failure will not occur after a
certain amount of wear comes into the ti It mechanism, the
amount of coarse alignment variation must be within specific
tolerance. The ti It mechanism shou Id be adjusted so that
the "band width" of the ti It mechanism wi
II
be within this
tolerance. Band width in the ti It mechanism is defined as
the maximum amount of coarse alignment variation JYleasured
between any two of the four ti It positions (Fig. 82). Of the
factors mentioned that affect the ti It ring position, only the
accuracy of adjustments can be controlled by the Customer
1
/
/
/
/
,
/
\
FIGURE
82.
Band Width
c
Band Width
O-Tilt
l-Tilt
2-Tilt
3-Tilt