[dneisler]

Can any tell me how splines are put inside parts. Example, maybe a axle hub?

[wms]

Most common way is to drag a broach thru the part.

By this, I mean a tool called a broach is drawn thru a hole in the part..the broach is made with the spline form ..and tapered..with cutting teeth..so as you draw it thru the part it gradually cuts deeper and deeper with each row of teeth until you have the final form..

Broaches can be pushed thru or pulled thru..depending upon the part and the machine and broach being used..

There are other possesses that will create internal splines but this is most common..

http://www.americanbroach.com/tools.htm

[Konrad]

Yes, or Rotary Broaching
Check this out [Video]
http://www.slatertools.com/rotary_broaching.htm

Konrad

[Machineguy]

Internal splines can also be produced with a gear shaper we do this for large diameter internal splines.