Helical Gears

Bookmark and Share
Helical Gears
Now that you’ve been introduced to the most common gear – the spur gear – let us turn our attention to another commonly used gear, the helical gear. Helical gears are similar to spur gears except that their teeth are cut at an angle to the hole (axis) rather than straight and parallel to the hole like the teeth of a spur gear.
Helical gears are used to connect non-intersecting shafts.
Helical gears are manufactured as both right and left-hand gears. The teeth of a left-hand helical gear lean to the left when the gear is placed on a flat surface. The teeth of a right-hand helical gear lean to the right when placed on a flat surface. Opposite hand helical gears run on parallel shafts. Gears of the same hand operate with shafts of 90º.
Helical gears are commonly used when efficiency and quieter operation are important.
Now let’s look at two configurations of helical gear connections: those connecting parallel shafts and those connecting non-parallel shafts.
Helical Gears Connecting Parallel Shafts
Helical gears connecting parallel shafts will run more smoothly and quietly than spur gears, particularly when the helix angle is great enough to ensure that there is continuous contact from one tooth to the next. A pair of helical gears used to connect parallel shafts must have the same pitch, pressure angle and helix angle, but they will be opposite hand gears (that is, one will be a left-hand gear; the other a right-hand gear).
Helical Gears Connecting Non-Parallel Shafts
Helical gears used to connect non-parallel shafts are commonly called spiral gears or crossed axis helical gears. If the shaft angle is 90 degrees, the gears will be of the same hand and the sum of the helix angles will be equal to the shaft angle (90 degrees).
Helical gears used on non-parallel shafts must have the same normal pitch and normal pressure angles. They may, however, be of the same or opposite hand depending on the shaft angle.