pignon
je vous rappelle ma méthode (déjà donnée sur le forum).
* Note 2: Here is a method which can be used to determine the module and pressure angle of
a gear wheel using only the tooth profile (the profile must be of involute shape).
Example: for a 20 teeth gear measure W3 and W2 using a sliding calliper or
a disc micrometer.
W3 – W2 = m x π x cosα (it’s the base pitch, m being the module and α the pressure angle)
Thus : m = (W3 – W2)/π cosα
Try a first calculation with α = 20°, if the result is very near a standard module (or diametral pitch equivalent) you have found the module and pressure angle.
If the result is far from standards, try a second calculation with α = 14°30’ (these teeth look
slimmer than the previous).
If no result is satisfactory:
- The module and/or pressure angle are perhaps not standard.
- The teeth profile is badly worn.
- The teeth are not of involute shape.
- The measures have not been taken the good way (see later).
For a gear having a different number of teeth you must take the measure on (n) and (n+1) teeth, (n) being chosen for the measure to be taken between two tangents of the tooth profile, not on an edge, whether it be on the top or in the bottom of the tooth (the calliper’s edge in that case).
This method works even if there is an addendum modification, and on helical gears too, it uses the properties of the involute curve.