Related Resources: gears

Gear Design for Known Center Distance and Ratio

Gear Design and Engineering

Gear Design for Known Center Distance and Ratio per. ANSI B6.7

Preview: Gear Design for Known Center Distance and Ratio

When it is necessary to use a pair of gears of given ratio at a specified center distance C₁, it may be found that no gears of standard diametral pitch will satisfy the center distance requirement. Gears of standard diametral pitch P may need to be redesigned to operate at other than their standard pitch diameter D and standard pressure angle φ. The operating diametral pitch P₁ at which these gears will operate is:

where:

N_p = Number of teeth in pinion
N_G = Number of teeth in gear
P₁ = Operating diametral pitch (in, mm)

where:

φ₁ = Operating pressure angle is
P = Diametral pitch as-built (in, mm)
P₁ = Operating diametral pitch (in, mm)

Thus although the pair of gears are cut to a diametral pitch P and a pressure angle φ, they operate as standard gears of diametral pitch P₁ and pressure angle φ₁. The pitch P and pressure angle φ should be chosen so that φ₁ lies between about 18 and 25 degrees.

The operating pitch diameters of the pinion D_p1 and of the gear D_G1 are:

Base diameters of the pinion D_PB1 and of the gear D_GB1

Basic tooth thickness, t₁, at the operating pitch diameter for both pinion and gear is:

Root diameters of the pinion D_PR1 and gear D_GR1

where:

b_c is the hob or cutter addendum for the pinion and gear.

Tooth thicknesses of the pinion t_P2 and the gear t_G2 are

Outside diameter of the pinion D_PO and the gear D_GO :