involute profiled modified?

[peteswift]

I have been trying to draw an accurate representation of a spline BS 3550 and have written a program to plot, from a given base circle, the involute between the major diameter and the minor diameter.

However is the spline form a true involute or does the cutter “modify” the involute as it revolves around the work?

I am doing this to answer a question of if we nitride a standard spline ant the surface grows by 0.02 mm how much does this affect the fit.

 

[dimjim]

I would thin the tooth thickness by the
same amount per side. The error would
be dependant on the module that you are
cutting.
You could plot the tooth and then offset
each side by the .02mm on each side of the
teeth and accomplish the same thing before
cutting the tooth space. Basically the
cutter would then not be a true involute
but after nitriding end up being close to
a true involute.
What is the function of the spline? If
a sliding fit, then you might want to use
the second method.