Page 249 - Practical Machinery Management for Process Plants Major Process Equipment Maintenance and Repair

Power Transmission Gears 231

Axis of gear-

Lead angle,

LDedendum ]

\y
Base circle Helix angle
dimeter
Face uidth
I
Pitch diameterJ
Helical gear

Heha1 rock
Figure 6-7. Helical gear and rack terminology.
4. Angle of Approacb--The angle through which the gear turns
from the time a particular pair of teeth come into contact until they
are in contact at the pitch point.
5. Angle of Recess-ne angle through which the gear turns from
the time a given pair of teeth are in contact at the pitch point until
they pass out of mesh.
6. Backlash-The difference between tooth thickness and the space
width in which the tooth meshes. The different backlash terms are
normal backlash, transverse backlash, radiak backlash, and axial
backlash.
7. Base Circle--The circle ji-om which the involute tooth form is
generated.
8. Base Pitch-The distance measured along the base circle from a
point on one tooth to the corresponding point on the adjacent
tooth.