Gear question

[bb218]

I have scrapped an old actuator and got some straight spur gears out of it. I would like to know what I have.
The gear measures 42.4 mm OD has a root diameter of 39.73 mm and 65 teeth. May be an inch application which measures 1.669" with a root diameter of 1.564" Have no idea what the Pressure angle is.


Mike

 

[xpylonracer]

Hi Mike

Formula is:
DP = (Number of teeth + 2) / Outside diameter
Doesn't work out to a whole number pitch with your quoted figures but is very close to 40 DP

Emgee

 

[bb218]

Emgee,
Thank you for the response, I think you are correct in the value being 40 DP Now a question, using a hand caliper it looks like 40 might be the tooth thickness at the pitch line ? Visually they appear to be .040 " thick in the middle of the tooth, is this where the 40 value comes from ?

Mike

 

[kvom]

The Diameterial Pitch (DP) is the number of teeth divided by the Pitch Diameter, If we assume perfect mesh than the pitch diameter is halfway between the root and crest, Given your numbers DP 40 looks correct. The DP is an inverse ratio of distance. If we assume 40 DP is correct then 40 = 65/PD or PD = 65/40 = 1.625". The circumference of the pitch circle = 1.625*pi = 5.105". Divided by 65 teeth means each tooth occupies .079" of the circle, and that includes one tooth and one space. So your measurement of the tooth width at midpoint of .040" is quite close to the calculated value.