Check out the latest projects here:Project Logs
Wikipedia states that 20° is the usual value but that 14½° is a less common value.
I have looked at ways of identifying the pressure angle of gears. The simplest procedure is to roll it in plasticine, slice through the impression and measure the angle. When I tried this it did not work very well for two main reasons:1. On the gears I was trying to identify (mini-lathe change gears) the plasticine would not pull away cleanly from the gear when trying to make an impression. Often material was left between the teeth of the gear or the impression was distorted.2. Cutting through the impression also causes distortion and the measured angle can differ depending on the direction of cut.In the end I resorted to a photographic method which is outlined on this webpage:http://mikesworkshop.weebly.com/change-gear-pressure-angle.htmlThis method seems to give good results and will positively differentiate between 14.5 degree and 20 degree gears.Mike
Take the gear, roll it in Plasticine to form a rack. Cut along the length of the rack so you can see the profile in elevation. Measure the angle