

How to tell gear pressure angles 20* vs 14 1/2*
Bought a coil winder but need some different change gears to wind the size wire I want.
Question how do I determine the pressure angle of the existing gears?? The catalogs warn that the pressure angles are not compatable.
Thanks, John

Pressure angle
Sir,
There are some brass geartooth gauges which are available for a small fee. These come as a bunch of different diametral pitches AND pressure angles. I even had one that was plastic at one time. Reid Tool Supply has one (steel) at $88.00 ! ! ! You ought to be able to find a cheaper version somewhere!.
Regards,
Jack C

geartooth gaugesanyone got a spare??
A gauge sounds like the way to go! Does anyone have a spare they would be willing to part with?? I only need one for 32 pitch. Willing to pay of course.
TIA, John

Take the gear to your local bearing supplier they should have a set of guages to check the pressure angle.

I copied this tip from an earlier thread on the same subject. Sorry but I can't credit the original poster, I didn't copy his name!
as long as you know the 'DP' of the gear the following will give you a good guide to the 'PA'. take a measurement over any number of teeth with whatever equipment you have,multiply the cosine of the 'PA' by 3.1416 and the divide by the 'DP' add this to your measurement, this should be the measurement over one more tooth if its not the same, change the cosine of the 'PA' and try again. example 10dp 14.5pa 30 teeth, the meas over 3 teeth .776,cos.986147 multiplied by 3.1416 and divided by 10 = .304 add .776=1.080 over 4 teeth.hope this helps

20 degree pressure angle gears are much more "pyramid" shaped than 14.5's. They are very easily recognised once you take a look at the 2 types.

Thanks Mudflap for reposting that handy tip

Like Mr. Wilson says  20° is more "pointy" and 14 1/2° is more square ended  same in the root.


as long as you know the 'DP' of the gear the following will give you a good guide to the 'PA'. take a measurement over any number of teeth with whatever equipment you have,multiply the cosine of the 'PA' by 3.1416 and the divide by the 'DP' add this to your measurement, this should be the measurement over one more tooth if its not the same, change the cosine of the 'PA' and try again. example 10dp 14.5pa 30 teeth, the meas over 3 teeth .776,cos.986147 multiplied by 3.1416 and divided by 10 = .304 add .776=1.080 over 4 teeth.hope this helps
What does 'take a measurement' mean? Over pins, across the chords, at what depth?

Originally Posted by HuFlungDung
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What does 'take a measurement' mean? Over pins, across the chords, at what depth?
I took it to be a span over teeth measurement. Just use a dial caliper.

Originally Posted by johnoder
Like Mr. Wilson says  20° is more "pointy" and 14 1/2° is more square ended  same in the root.
Here is a link to a web page with a diagram:
http://shopswarf.orcon.net.nz/spur.html

Get a worm of modelling clay on the bench and roll a gear along it, cut through the impression (along the length of the worm) and look at the tooth angle of the rack you have made in the clay, it is easy to measure the angle, send the $88 to me!
Peter
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