Figure 14-4.--Helical gears.
toward the right, the gear is right-handed. If the helix
at an angle to each other, as long as their axes do not
moves upward to the left, the gear is left-handed.
intersect (fig. 14-4).
To mill a helical gear, you need a dividing head, a
Helical gears operate more quietly and smoothly
than spur gears because of the sliding action of the spiral
tailstock, and a lead driving mechanism for the dividing
teeth as they mesh. Also, several teeth make contact at
head (fig. 14-5). These cause the gear blank to rotate at
the same time. This multitooth contact makes a helical
a constant rate as the cut advances. This equipment is
gear stronger than a comparable spur gear. However,
an integral part of a universal knee and column type of
the sliding action of one tooth on another creates friction
milling machine.
that could generate excessive heat and wear. Thus,
When a helical gear is manufactured correctly, it
helical gears are usually run in an oil bath.
will mesh with a spur gear of the same diametral pitch
A helical gear can be either right-handed or
(DP), with one gear sitting at an angle to the other. The
left-handed. To determine the hand of a helical gear,
dimensions of a helical gear would be the same as those
simply put the gear on a table with its rotational axis
of a comparable spur gear if the helical gear's teeth were
perpendicular to the table top. If the helix moves upward
14-6