Methods for determining the specifications of gears

12/07/2021

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 p_zof a helical gear can be presented with quation:

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

The number of teeth z and normal module m_n can be obtained using the method for Spur gear (explained in the previous topic). In order to obtain p_z, determine d_a 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, b_a. lead p_z, 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

m_n = 2.5

   a_n = 20 degree

   b = 19.5 degree

(For details, please refer to the table below)