A cutter, then, of 8 diametral pitch is the one to use for this particular gear. To illustrate, if the pitch diameter of a helical gear is 6.718 and there are 38 teeth having a helix angle of 45 degrees, the transverse diametral pitch equals 38 divided by 6.718 = 5.656 then the normal diametral pitch equals 5.656 divided by 0.707 = 8. This normal pitch is found by dividing the transverse diametral pitch of the gear by the cosine of the helix angle. The cutter should be of the same pitch as the normal diametral pitch of the gear. The normal pitch varies with the helix angle, hence, the helix angle must be considered when selecting a cutter. Pitch of Cutter to be Used.-The thickness of the cutter at the pitchline for cutting helical gears should equal one-half the normal circular pitch. If each helix angle is less than the shaft angle, then the sum of the helix angles of the two gears will equal the angle between the shafts, and the helix angle is of the same hand for both gears if the helix angle of one of the gears is larger than the shaft angle, then the difference between the helix angles of the two gears will be equal to the shaft angle, and the gears will be of opposite hand. Helical Gears Shafts Parallel, Center Distance Approximate Design Equations and CalculatorÄetermining Helix Angles.-The following rules should be observed for helical gears with shafts at any given angle. Related Resources: calculators Helical Gears Shafts Parallel Center Distance Approximate Design Equations and Calculator
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