Regression analysis: Simple Linear Regression Multiple Linear Regression
Helical and Herringbone Gear Design and Specifications
1. Helical Gears and Herringbone Gears
Helical gears are used instead of spur gears for heavy loads and high speeds and especially where the
noise level is to be kept very low. Helical gears may be used to connect parallel and non-parallel shafts.
A special type of helical gear called the “herringbone.” This is a double helical gear with teeth opposed.
This construction eliminates the end thrust factor.
Example of Helical Gear Specifications:
K HG 1 – 20 R
R = Direction of helix (right)
20 = number of teeth
1 = module
HG = Type (Ground Helical Gear), H = Helical Gear
K = SCM440 (alloy steel), S = S45C (medium strength steel)
Helical Gears
A helical rack is shown in the figure below, in which lines LM and NO represent the center lines
of two consecutive gear teeth. Angle ψ is the helix angle of the rack.
2. The distance LN in the transverse direction of the helical rack is defined as the transverse pitch,
Pt, while the distance LP in the direction normal to the helix angle is the normal pitch, Pn. Evidently,
Also, the distance LO, in the axial direction, as shown in the figure, is defined as the axial pitch, Px of the
helical rack, which is related to the transverse circular pitch, Pt as follows,
Setting Pnd and Ptd as normal and transverse diametral pitches of the helical rack,
And
Substituting respective equations, the following relation for normal pitch diameter can be obtained,
In the figure, the section of helical rack, along transverse section A-A and a normal section B-B are
shown. Because of the helix angle, it is necessary to define two pressure angles øt and øn. The two
pressure angles, transverse pressure angle, øt and normal pressure angle, øn are related by
Further, in helical gear, the face width, F must be sufficiently large enough for the face advance to be
greater than the transverse pitch, Pt for a given helix angle, ψ. The ratio of face width, F to the transverse
pitch, Pt is sometimes called the contact ratio for helical gears. The general recommendation is
3. Contact of Helical Gears
Example:
It is required to replace a pair of gear consisting of 20 o full depth spur gears of 24 teeth and 60 teeth
having a diamteral pitch equal to 6, by helical gears of 6 diametral pitch and 20o full depth.
The center distance:
Speed ratio:
For the helical gear pair, it is necessary to keep a center distance of 7 cm and speed ratio of 2.5
