Quote Originally Posted by Al_The_Man View Post
An example application where locomotive car wheels are press fit on to the axle.

The boring mill must bore a spiral groove in one shot through the wheel bore.
The tool on the boring bar has a convex shape that results in a concave groove......Al.
What is the function of the spiral groove? I could understand it for an oil groove but I doubt whether the wheel is intended to spin on the axle .

Lubrication during a multi-hundred ton press fit to prevent galling?