TB 9-5220-212-40
7. Equipment Setup. The conditions in a through e below must prevail before starting
a. TI must be supported at same points used by manufacturer. If support feet are
missing, replace at points specified by manufacturer.
b. TI must be level as indicated by bench level.
c. Temperature of mass must be in equilibrium.
d. Vibration must be excluded.
e. TI must be clean.
8. Flatness Tolerance
a. Performance Check
(1) Select carriage from autocollimator accessory equipment with support points
approximately 8 percent of TI width.
NOTE
Use 4-inch carriage if 8 percent of TI width exceeds 4 inches.
(2) Designate north, south, east, and west as shown in figure 1.
(3) Set up perimeter, diagonal, and centerlines on TI as shown in figure 1, following
sequence listed in (a) through (d) below:
(a) Lay out 2 diagonal lines, making certain that they bisect physical center of TI.
NOTE
Any marks made on TI surface must not be made where
carriage will travel. If possible, mark only on clamping ledges
of TI.
(b) Lay out even number of increments (stations) along each diagonal line,
using length of carriage base selected in (1) above. Each diagonal line will have same
number of stations. Do not extend stations onto clamping ledges of TI.
(c) Lay out 4 perimeter lines connecting with diagonal lines, and observe
conditions listed in 1 through 3 below:
1 Each perimeter line will have even number of stations.
2 No station will extend to clamping ledge of TI.
3 North perimeter line will have same number of stations as south
perimeter line, and east perimeter line will have same number of stations as west
perimeter line.
(d) Lay out centerlines, observing conditions listed in 1 through 3 below:
1 Each centerline will pass through physical center of TI.
2 Ends of centerlines will tie at midpoints of respective perimeter lines.
3 Each centerline will have same number of stations as respective parallel
perimeter lines.