Pitch diameter

Basically, two engaging gears are two cylinders of different diameter with teeth machined on their periphery (Fig. 29-82). A gear is defined by its basic diameter (pitch diameter), its width, the number of teeth, and the angle that the teeth make in respec t to the axis. 

The ratio between the input-to-output shaft speeds is determined either by the ratio of the two pitch diameters or the ratio between the number of teeth ... 

The ratio between the pitch diameter and the number of teeth is called the diametral pitch, and for two gears to mesh, they must have the same diametral pitch. The diametral pitch is standardized and is always an integer. For gears used in process machineiy, the diametral pitch varies between 6 (coarse) and 20 (fine). 

D = pitch diameter of the larger pulley (mm) d = pitch diameter of the smaller (faster) pulley (mm)... 

Power rating for smaller pulley, with preferred pitch diameter of... 

Belt section Pitch diameter (mm) Outside diameter ... 

The limits of tolerances on the pitch diameter will be 0.8% Courtesy Goodyear. See also IS 3142 and ISO 4183... 

An important consideration of a gear unit is the pitch line velocity (PLV), which is the product of the gear or pinion pitch diameter and the shaft speed of the gear or pinion. 

The measurement of tlie pitch diameter of the tliread of a fitting is noniuilly distributed with mean 0.4008 inch and standard deviation 0.0004 inch. The specifications are given as 0.4000 0.0010 inch. Wliat is tlie probabilily that a defective fitting will occur ... 

Figure 3-22 shows the general dimensions of an open-belt drive. For V belt drives, the pulling diameter D and d are pitch diameters [11]. The quantity C in the center distance, 0 in the contact angle for the smaller pulling, and 2x is the angular deviation from a 180° angle of contact. 

This can also be expressed in terms of sheave pitch diameter. This is... 

Find the V-belt speed using Equation 3-16 using pitch diameters of sheaves. Speed must be below 600 ft/min (or 100 ft/s). 

Knowing the speed (in rpm) of the smallest sheave and its pitch diameter, find the horsepower capability per V bell using the appropriate table for the V-belt type to be used (see Tables 3-9-3-16). 

Pitch diameter (of either the drive sprocket or driven sprocket) is generally on a theoretical circle described by the centerline of the chain as it passes over the sprocket. 

Most worms are cylindrical in shape with a uniform pitch diameter. However, a variable pitch diameter is used in the double-enveloping worm. This configuration is used when increased load capacity is required. 

Belt-drive ratios may be calculated if the pitch diameters (see Figure 44.5) of the sheaves are known. This coefficient, which is used to determine the driven speed given... 

Figure 44.5 Pitch diameter and center-to-center distance between belt sheaves...

To approximate the rotational speed of the belt, the linear speed may be calculated using the pitch diameters and the center-to-center distance (see Figure 44.5) between the sheaves. This method is accurate only if there is no belt sag. Otherwise, the belt rotational speed obtained using this method is slightly higher than the actual value. 

BD = Ball or roller diameter PD = Pitch diameter yS = Contact angle (for roller = 0) n = Number of balls or rollers... 

Linear and circular measurements that define gears and are used in their specification and design are center distance, offset, pitch diameter, diametric pitch, axial pitch, base pitch, and axial base pitch, lead, and backlash. 

A pitch circle is illustrated in Figure 57.29. The imaginary circle can be drawn to illustrate the motion of a gear in operation. The diameters of these imaginary circles are referred to as the pitch diameters of the gears. The center distance of two correctly meshed gears, illustrated in Figure 57.30, is equal to one half the sum of the two pitch diameters. 

C = Center distance, inches Di = First pitch diameter, inches D2 = Second pitch diameter, inches... 

Diametric pitch is a whole number used to specify the ratio of the number of teeth in a gear to its pitch diameter. Stated another way, it specifies the number of teeth in a gear per inch of pitch diameter. For each inch of pitch-circle diameter, there are pi (jr = 3.1416) inches of pitch-circle circumference. Therefore, the diametric pitch provides the number of teeth for each 3.1416 inches of circumference along the pitch circle. 

Figure57.31 Determining center distance with known pitch diameter...

The mathematical relationship of the circular pitch to the pitch-circle circumference, number of teeth, and the pitch diameter is shown in the following equations ... 

C = Pitch circle circumference (jtD), inches D = Pitch diameter, inches N = Number of teeth p = Circular pitch, inches jr = pi (3.1416)... 

Example 1 What is the circular pitch of a gear with 48 teeth and a pitch diameter of 6 inches ... 

Example 2 What is the pitch diameter of a 0.500-inch circular-pitch gear with 128 teeth ... 

The mathematical relationship of pitch diameter, diametric pitch, and number of teeth is shown in the equations below. As with any equation, one of the variables can be calculated if any two are known. 

D = Pitch diameter, inches P = Diametric pitch, inches N = Number of teeth... 

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