DEDENDUM (fig. 3-1). The distance between the
pitch circle and the bottom of the tooth space.
WORKING DEPTH (fig. 3-1). The depth to which
the teeth of a gear enter into their mating space.
CLEARANCE (root) (fig. 3-1). The distance
between the top of a tooth and the bottom of its
WHOLE DEPTH. The total depth of the tooth
space and also the sum of the addendum and
INTERFERENCE. Contact between mating gears
at some point other than along the line of action.
FILLET (fig. 3-l). The concave radius that joins
the tooth profile and the bottom of the tooth space.
Tests and inspections according to the PMS are
minimum requirements only. When defects are
suspected, or operating conditions indicate, inspections
should be made at more frequent intervals.
When opening gear cases for inspection, use
extreme care. Even under normal conditions, when the
covers are lifted the possibility of getting foreign
particles inside the gear case is high. The engineer
officer should evaluate all ongoing work in the engine
room, especially in the areas over the gears. Besides
evaluating the work, the engineer officer must schedule
all necessary MRG inspections.
You must be sure that gear sumps are cleaned after
all work to the MRG has been completed. Thoroughly
inspect the gear sump and remove any foreign material.
Absolute cleanliness is required before filling the gear
sump with clean oil.
Oil should be renovated before returning it to the
sump. If new oil is used, you must be careful to remove
any water or foreign particles. Cloth bags placed in the
lube oil (LO) strainer baskets after major repairs is
another required precaution. The bags stop foreign
particles from passing through the gear train and
bearings. Once the proper temperatures and pressures
have been reached in the LO system, inspect the MRG
for leaks and all sight-flow indicators for proper flow.
The following paragraphs discuss some of the
inspections, tests, and problems that may occur to
BACKLASH. Backlash is the play between the
surfaces of the teeth in mesh measured at the pitch circle.
The backlash will increase with wear, and can increase
considerably without causing trouble. On some gears
that are recut, the backlash does not affect operation or
Figure 3-1.Gear tooth nomenclature.