TM 9-1290-357-15
the time required for the needle to complete five
the azimuth fixture, rotate the instrument with
periods. A period of the needle is the time re-
any combination of azimuth and orienting move-
quired for it to move from its maximum dis-
ments for 1600 mil increments and return with
placed position to right of the point of equili-
the azimuth fixture ring. Repeat for 6400 mils.
brium, to the extreme left, and back to the initial
The horizontal reticle line should not deviate more
position.
than 2.25 mil from a target. When reversing direc-
tion the displacement between reticle line and
d. If the total time is more than 40 seconds,
target must not exceed 0.5 mil. When testing se-
or more than 8 seconds per period, the magne-
parately, the azimuth worm will not displace the
tism of the needle is weak.
reticle and target more than 1.5 mils and the
e. If there is a weak needle, out of shape, or
orienting worm movement will not displace the
north and south does not line up with the respec-
reticle and target more than 0.75 mils.
tive indexes, replace needle in accordance with
b. Vertical Travel. When the telescope is ele-
vated or depressed the reticle must not deviate
more than 0.75 mil from a plumb line. The stop
5-58. Clamp and Releasement of Plungers
mechanism should permit at least 8 degrees (142
a. Operate the olive drab and red plungers
mils) of movement.
to see that the magnetic needle can be released
for rotation.
b. If by operation of either plunger it fails
Place instrument on a leveled surface plate. Also
to clamp or release the needle, this indicates a
place a collimating telescope in a V block on the
damaged part and/or component necessitating re-
plate. With the level bubble centered, measure
pair or replacement of the part or component.
from the center of the eyepiece to the center of
Repair or replace as required.
the collimator. Construct a target using this same
dimension and place it 150 yards away. Sight on
5-59. Azimuth Worm Throwout Lever
the target through collimator and instrument. If
lines of sight are more than 0.5 mil beyond the
a. Operate the azimuth worm throwout lever
measurement, adjust level vial to suit (para 539
to see that it moves freely without binding, and
above).
that it will fully disengage and engage the worm
and worm gear. There must be no drag of teeth
when lever is pushed to the outward position
and the azimuth scale index is rotated. Binding
a. Place aiming circle on a level surface plate.
of the lever ind cates a malfunctioning of the
The bubble in the circular level vial should be
throwout shoe, and drag of the teeth indicates
centered in the etched lines on top of the vial
improper adjustment of either the azimuth com-
and should remain centered when instrument is
pression spring or ball cap and socket of the
rotated 6400 mils.
worm mechanism.
b. If bubble in the circular level vial does not
b. Bent throwout shoe or burrs between the
remain centered turn the adjusting screws (fig.
shoe and body may cause the throwout shoe to
stick and prevent complete disengagement of the
etched lines on the top of level vial.
worm. Remove the burrs with a fine mill file
or oilstone and polish the surface with crocus
5-57. Magnetic Needle
cloth. Replace bent or broken shoe.
a. Place aiming circle on a level surface.
5-60. Tripod M5
Note. No magnetic materials should be in close proxim-
ity to the instrument during the procedure.
a. With the proper adjustment of the clamp-
ing screw on the tripod M5 (fig. 1-1) the ball
b. By attraction of an iron object, such as a
and socket should have enough tension to support
screwdriver, displace the magnetic needle about
the aiming circle M1 in any position.
30 from the equilibrium position. Remove the
screwdriver allowing the needle to swing to the
right and left of its equilibrium position.
b. Check the tripod leg assembly joints at the
c. Using a watch with a sweep hand measure
tripod bend for proper tension and adjust as re-
