Pressure angle of gears

[drmico60]

Does anyone have a good way of measuring the pressure angle of gears?
I have tried measuring the curvature of gear teeth, from photographs and using a USB microscope and then using Ivan Laws circular approximation to the involute to calculate the pressure angle but the results are very inconsistent. Is there a simple way of reliably measuring the pressure angle of a gear using normal measuring tools? Any ideas greatfully received.
Mike

[HuFlungDung]

If you call a set of gear pitch gauges, in both 14.5° and 20° PA, 'normal measuring tools', then yes

The thickness of the tooth at the pitch circle is the same, regardless of the pressure angle, but the tip thickness is quite markedly different, and the 14.5° gauge will not go deep enough into a 20 degree gear.

If you have some cad facilities, I'd recommend that you sketch up both iterations of the same tooth count and print out for a comparison to the real gear you might have in hand.

Failing that, you could also, from a full scale cad drawing, figure out how deep a pin should descend into the tooth space while attaining tangential contact in two places on the pin. You'd want to pick a pin diameter that is larger than that recommended for measuring the gear pitch diameter, because that particular size pin is designed to measure at the pitch circle, where there is no distinguishable difference between the gears, no matter what the pressure angle.

[drmico60]

Thanks, I have now convinced myself that I have a 20 degree pressure angle gear. My method is described here:
http://mikesworkshop.weebly.com/chan...ure-angle.html
Mike

[MikeZee]

Good answer.