|Module||= mn = = or|
|Normal pitch in mm||= pn = mn.p or|
|Normal base pitch in mm||= pb = pn.cosa|
|Number of teeth||= z = of|
|Pitch diameter in mm||= d = z.mn of or da+2.mn|
|Tip diameter in mm||= da = mn.(z-2) of d-2.mn or d-|
|Face width in mm||= b = 10.mn|
|Tooth depth in mm||= h = 2,16.mn of 2,16. for a = 14°30’|
|= h = 2,25.mn or 2,25. for a = 20°|
|Addendum in mm||= ha = mn or|
|Dedendum in mm||= hf = 1,16.mn or 1,16. (a = 14°30’)|
|= hf = 1,25.mn or 1,25. (a = 20°)|
|Thickness below the tooth in mm||= H = approx. 1,6.mn minimum|
|Centre distance in mm||= A =|
|Root diameter||= df = d+2,5.mn|
At toothing of internal gear on a Fellows- or similar machine through gear cutters the obtained dedendum is 1.25 m instead of 1.16. m.
In a transmission with internal gears there are no special precautions to take when it comes to an internal gear with a large number of teeth and a pinion with a small number of teeth. On the other hand, where the teeth numbers approach each other at a reduction, there will be a moment that gripping is no longer possible.
One assumes that for a normal gear with pressure angle 14°30′, this difference must amount to at least 12 teeth; for stub gear (reduced tooth depth) and with pressure angle 20° this difference can be reduced to 7 teeth.
The chart below allows a quick way to define the maximum number of teeth of the cutter for cutting of gears with internal teeth.
Z0: maximum number of teeth of the cutter.
Z1: number of teeth of the gear with internal teeth.