TB 9-5210-202-40
(4) Repeat (2) and (3) above using sequence and TI combinations as listed in table 3
of example A. Both surfaces of each TI must be checked.
EXAMPLE A:
NOTE
Each distortion fringe is multiplied by 11.6 microinches-
wavelength of the monochromatic light.
Sequence
Distortion (fringes)
Distortion (micro
inches)
B on A
A + B = 1/10
1.16
C on A
A + C = 1/4
2.90
D on A
A + D = 1/5
2.32
C on B
B + C = 1/10
1.16
D on B
D + B = 1/10
1.16
D on C
C + D = 1/5
2.32
NOTE
Place each surface of each TI upon the same surface (top or
bottom) of each of the other TIs.
NOTE
If the fringes bow around the contact point, convexity is
indicated (+) and the fringe distortion has a positive sign. If
the fringes bow away from the contact point, concavity is
indicated (-) and the fringe distortion has a negative sign.
NOTE
The contact point is determined by downward pressure on the
flat at a point directly above one of the edges running parallel
to the interference bands. If bands remain the same distance
apart, that edge forms the line of contact. If the bands tend to
decrease in number, the opposite edge forms the line of contact.
(5) Determine deviation of TI (each flat) by arranging distortion values from table 3
(Example A) in an equation, such as Example B, and solve algebraically. The maximum
deviation should not exceed 0.000003 (approx. 1/4 of one band) inch.
5