Dimension across pins, ANSI B92.1 1

[as321]

I'm trying to specify internal splines using ANSI B92.1 I've gotten through everything but the dimensions across pins just fine, here is what I have so far:

ANSI B92.1-1996 Internal Involute Spline
Class 5
Fillet Root Side Fit
Teeth: 36
Pitch: 16/32
Pressure angle: 30
Base Dia: 1.949"
Pitcch Dia: 2.25"
Major Dia: 2.363"
Form dia: 2.317"
Minor dia: 2.188"/2.193"
Circular space width: 0.0982 (MIN)

The trouble is when I get to measurment between pins. I'm using a pin diameter of 0.108, but I don't understand how I'm supposed to arrive at dimension between pins from the equations in B92.1.

Specifically: "inv (phi i) = s/D + (inv (phi D) di/Db)"

What is "inv"? I've never seen this function before.

 

[israelkk]

Inv is the involute function.

inv(phi)=tan(phi)- phi in (phi in radians).

 

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