Methods for determining the specifications of gears

The Helix angle is what differs helical gears from spur gears and it is necessary that the helix angle is measured accurately. A gear measuring machine can serve this purpose, however, when the machine is unavailable you can use a protractor to obtain an approximation.
Lead pz of a helical gear can be presented with quation:


Given the lead pz, number of the teeth z normal module mn, the helix angle b can be found with the equation


The number of teeth z and normal module mn can be obtained using the method for Spur gear (explained in the previous topic). In order to obtain pz, determine da be measuring the Tip diameter. Then by using a piece of paper and with ink on the outside edge of a helical gear, roll it on the paper pressing it tightly. With a protractor measure, the angle of the mark left printed on the paper, ba. lead pz, can be obtained with the following equation:



For a calculation example            

Using excel to make a calculation table, the following results are calculated based on the gear product (was broken)  to give the basic parameters:
   z = 24

   mn = 2.5
   an = 20 degree
   b = 19.5 degree

(For details, please refer to the table below)




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