### Gear Design for Known Center Distance and Ratio

Gear Design and Engineering

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

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:

Np = Number of teeth in pinion
NG = 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 Dp1 and of the gear DG1 are:

Base diameters of the pinion DPB1 and of the gear DGB1

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

Root diameters of the pinion DPR1 and gear DGR1

where:

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

Tooth thicknesses of the pinion tP2 and the gear tG2 are

Outside diameter of the pinion DPO and the gear DGO :

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