Spur and Helical Gear Mechanical Drawing Specifications Requirements

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Defining a gear for manufacturing, or procurement requires engineering and manufacturing information. Typically, this information is provided on a engineering drawing. The dimensional requirements of the gear may be expressed as a mechanical detail drawing dimensional data or specified by use a requirements chart on a mechanical drawing.

The following is a typical gear manufacturing requirements chart for Spur and Helical gears.

Spur Gear
Description (See Below)	Nomenclature
A	Number of Teeth
B	Diametral pitch or module
C	Pressure angle
E	Standard Pitch Diameter
F	Tooth Form
G	Max. Calc. Circular Thickness on Std. Pitch Circle
K	Maximum Tooth to Tooth Total Error
L	Specification Master
M	Outside Diameter
J	Maximum Total Error
H	AGMA Quality / Tolerance Class

Helical Gear
Description (See Below)	Nomenclature
A	Number of Teeth
B₁	Normal Diametral Pitch or Module
C₁	Normal Pressure Angle
D	Helix angle
D₁	Hand of Helix (Right or Left)
E	Standard Pitch Diameter
F	Tooth form
G₁	Max. Calc. Normal Circular Thickness on Standard Pitch Circle
J	Maximum Total Error
K	Maximum Tooth to Tooth Total Error
L	Master Specification
M	Outside Diameter
H	AGMA Quality / Tolerance Class

Description:

A. Number of Teeth: Total number of teeth on gear.

B. Diametral Pitch: Ratio of the number of teeth on the gear to the number of inches in the standard pitch diameter.

B₁) Transverse Diametral Pitch: Diametral pitch in the transverse plane.

C) Pressure Angle: Angle between the gear tooth profile and a radial line at the pitch point.

C₁) Normal Pressure Angle: Pressure angle in the normal plane.

D) Helix Angle: Angle between the pitch helix and an element of the pitch cylinder, or any specified feature.

D₁) Hand of Helix: Direction in which the teeth twist along the axis. (right hand twists clockwise, and left hand twists counterclockwise).

E) Standard Pitch Diameter: Diameter of the pitch circle, or the number of teeth divided by the transverse diametral pitch.

F) Tooth Form: Normally defined within a detail view on the mechanical drawing, information delineated is one or more of the following; Standard addendum, long addendum, short addendum, modified involute or other.

G) Maximum Calculated Circular Thickness on Standard Pitch Circle: Tooth thickness which provides required minimum backlash with gear assembled within mating gear at minimum center distance.

G₁) Maximum Calculated Normal Circular Thickness: Circular tooth thickness in the normal plane.

H) AGMA Quality / Tolerance Class: Defines the accuracy of the gear.

J) Maximum Total Error: Cumulative or actual tolerance values permitted by the AGMA quality / tolerance class.

K) Maximum Tooth to Tooth Total Error: Tolerance value is given within the AGMA quality / tolerance class.

L) Specification Master: This is used to specify the check tool by part number or industry specification for backlash or to verify gear interface parameters.

M) Outside Diameter: This is the largest and major diameter of the gear. The parameter is normally verified with the mating Specification Master Gear.