Methods for determining the specifications of gears

In fact, when repairing machines, engineers will encounter many problems that need to be solved, one of the fairly basic problems is the calculation and redesign of the damaged gear part of the gear transmission, and the difficultly there is not drawing of the gear part and the part model has been severely damaged. So how to solve the above problem?

The blog below outlines the basic way to solve this problem!

Illustrated below are procedural steps to determine the specifications of a spur gear

Step 1. Count how many teeth a sample spur gear has  Z          Picture10


Step 2. Measure its tip diameter da                                                  Picture11


Step 3. Estimate an approximation of its module, assuming that it has an unshifted standard full depth tooth, using the equation:



Step 4: Measure the span measurement of k and the span number of teeth. Also, measure the k-1. Then calculate the difference.

Span number of teeth k=    Picture13                                                                                       Span measurement Wk =   Picture13

Span number of teeth k-1 = Picture13                                                                                      Span measurement Wk-1 = Picture13
                                                                                                                                                                                    The defference  = Picture13

Step 5: This defference represents Pb = pm*cosa

Select module m and presure angle a from the table on the below (attachment table1)
                                                m =  Picture13
                                                a =    Picture13

Step 6: Calculate the profile shift coefficient x based on the above m and presure angle a and span measurement W.

                                               x =   Picture13

To find the calculation method, please see at the next topic!

Attachment table

 This table deals with the presure angle 20o and 14.5o only. There maybe cases where the degree of the presure angle is difference. Tooth profile come with deep tooth depth or shallow tooth depth, other than a full tooth depth.

Author: Phan Nguyen

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