Fellows Stub Tooth, 9 teeth on a 10 tooth blank? Help..
Fellows Stub Tooth, 9 teeth on a 10 tooth blank? Help..
(OP)
I have a pinion spur gear that I need to mate a new gear with. It is an 8/10 Fellows Stub tooth with 9 teeth on a 10 tooth blank. Pitch diameter the # teeth divided by the diametral pitch. I know for Fellows Stub Tooth gears the numerator of the 8/10 diametral pitch is the one to use to establish pitch diameter (the 8), but what of the # of teeth? The pinion prints says the pitch diameter is 1.25. That means they were using the # of teeth for the blank size (10), not the actual # of teeth (9). Is this correct? I do not understand what 9 teeth on a 10 tooth blank means, and whether to use 9 or 10 to establish pitch diameter.





RE: Fellows Stub Tooth, 9 teeth on a 10 tooth blank? Help..
For gear transmission rate calculations you need to use the number 9. For center distance calculations you need to use the pitch diameter of 1.25.
RE: Fellows Stub Tooth, 9 teeth on a 10 tooth blank? Help..
RE: Fellows Stub Tooth, 9 teeth on a 10 tooth blank? Help..
RE: Fellows Stub Tooth, 9 teeth on a 10 tooth blank? Help..
1) The meaning of Fellows stub – tooth system
For example for DP 8/10:
a- use DP 8 for pitch diameter calculation
d = N / DP = 9 / 8 = 1.125 "
b- use DP 10 for addendum and dedendum calculation
addendum = a = 1 / DP = 1 / 10 = 0.1”
dedendum = 1,25 / DP = 1.25 / 10 = 0.125”
The above values are the same as DP 8 stub – tooth gear with 0.8 / DP addendum (addendum = 0.8 / 8 = 0.1” )
and 1 / DP dedendum ( dedendum = 1 / 8 = 0.125”).
2) The meaning of the use of 10 teeth blank for 9 teeth gear, for example.
This is an old and bad way of specification for one Profile Shift gear.
The pitch diameter for DP 8 gear with 10 teeth is
d = N / DP = 10 / 8 = 1.250”
The pitch diameter for DP 8 gear with 9 teeth is
d = N / DP = 9 / 8 = 1.125”
Profile shift = (1.250 – 1.125) / 2 = 0.125” / 2 = 0.0625 = x / DP
x = 0.0625 (DP) = 0.0625 (8) = 0.5
3) Conclusion:
The stub - gear mentioned will be better and clearer specified as:
DP = 8; N = 9; x = 0.5; addendum = 0.8 / DP and dedendum = 1 / DP