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TM 9-254
3-7.
Worm and Worm Gear Mechanisms - Continued
(2)
The only remedy for this condition is to install a screw that fits snugly in the housing and make sure that
the dog-point fits in the slot of the socket.
i.
Binding. A binding or uneven movement is caused by a bent worm, the presence of dirt between the worm
and worm gear, or by a burr on one of the teeth. If a burr is present, remove it with a stone, file, or scraper. Polish the
area with crocus cloth, clean and lubricate then assemble the parts and check that the movement is smooth.
Section IV. TUBULAR LEVEL ASSEMBLIES
3-8.
Level Vials.
a.
General. The ordinary tubular level vial is essentially a straight glass tube closed at both ends and partially
filled with a liquid, leaving a small free space or bubble. The vial must provide the necessary accuracy and durability.
b.
Uses. The tubular level vials are used in instruments to establish a true horizontal position for a known
starting point of operation. Another use is to indicate the angular rotation of a mechanism in a vertical plane. The purpose
of the markings is to indicate when a true horizontal plane exists.
c.
Eccentric. The eccentric is an adjustable device to eliminate level vial error during final adjustments of the
instrument. The reasons for using a two piece eccentric or a three piece eccentric are as follows:
(1)
A two piece eccentric is used to correct for slight defects in the level vial tube and level vial mount when
setting up a true horizontal plane.
(2
A three piece eccentric is used to correct for slight defects in the level vial tube and level vial mount
when setting up a true horizontal plane that must also be rolled in a vertical axis.
d.
Removal of Two Piece Eccentric and Tubular Level Vial (fig. 3-24). The proper method of removing a two
piece eccentric and tubular level vial is as follows:
(1)
Use fabricated eccentric tool (5) (fabricate per fig. C-2, app C) to remove external threaded ring (4) and
eccentric (3).
(2)
Rotate level vial cover (7) to gain access to the viewing slot of the level vial tube (2).
(3)
Insert a common straight blade screwdriver (6) or similar device into the exposed viewing slot of level
vial tube (2). Carefully slide level vial tube from bracket (1) and level vial cover (7).
(4)
Remove straight pin (8) only if necessary to replace.
e.
Installation of Two Piece Eccentric and Level Vial Tube (fig. 3-24). The proper method of installing a level vial
tube and two piece eccentric is as follows:
3-21
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