TM 9-1290-357-15
Table 51. Tolerances for Aiming Circle, M1 -- Continued
Tolerances
Limit
Rebuilt
New
of
instru-
instru-
Item
Condition
service-
ments
ments
ability
1.5
1.5
1.5
Coincidence of 60-mil
graduations with
testing target (mils).
None
None
Parallax
None
At 75 to 85 yards from
instrument.
0.75
0.75
0.5
Spindle clamp
Effect on leveling caused by
clamping and unclamping
shall not exceed (mils).
0.75
0.75
0.5
Azimuth mechanism
Backlash (mils).
2.0
2.0
1.5
Error in reading azimuth
angles including backlash
shall not exceed (mils).
0.75
0.75
None
Backlash (mils).
Orienting mechanism
None
None
None
Backlash (mils).
Elevating mechanism
Same
Same
Less
Magnetic needle
Half period (seconds).
than
4.0
1
Apply the correction value to all line of sight readings if the error exceeds 0.5 mil.
5-50. Vibration Test
5-52. Parallax
Caution: Lock compass needle before vibrat-
a. Test. With the focusing sleeve in the center
ing.
of its movement, and sighting on an 80 yard
target, check for parallax by moving head verti-
a. Utilizing a suitable adapter, mount the aim-
tally and horizontally. Observe any movement be-
ing circle on the vibration tester (fig. 46) and
tween reticle and target.
vibrate the instrument in a verticle plane for a
period of two and one half minutes 15 seconds
b. Adjustment. To remove any apparent paral-
at an amplitude of not less than 1/16-inch (1/8-
lax, adjust objective cell.
inch maximum total movement) at a frequency
of 30 cycles per second.
5-53. Backlash
b. After vibration, remove the aiming circle
a. Azimuth Mechanism. With the instrument
and adapter from the tester (fig. 46) and in-
mounted on the azimuth test fixture as indicated
spect for dirt, scratches, broken or defective com-
in paragraph 5-52a above, set azimuth scale and
ponents, clean or repair as required.
micrometer at zero. Rotate the instrument with
the orienting knob until the vertical reticle line
is superimposed on a clearly defined target. Note
5-51. Eyepiece Focus
micrometer reading, then continue a few mils in
a. Test. With the aiming circle mounted on
the same direction. Reverse the direction and
the azimuth fixture as indicated in paragraph
again view target without overpassing. The dif-
550 above, direct the line of sight into the col-
ference between readings must not exceed 0.75
limator. Set the collimator scale to 150 yards.
mils. Adjust mechanism if required.
Place focusing sleeve in center of its movement,
b. Orienting and Elevation Mechanisms. Make
and sight into collimator. Observe whether tar-
checks similar to a above, to determine backlash
get and reticle images are well defined.
does not exceed 0.75 mils in these mechanisms.
b. Adjustment.
Lines scribed on ends of knobs will aid in estima-
ting mil measurements.
(1) Adjust eye and field lens assembly to
obtain good reticle definition.
(2) Adjust objective cell to obtain definition
a. Horizontal Travel. With the instrument on
of the field.
5-12
