I am having a problem with milling a slot in thin wall (.014) telescoping brass tubing. There is a .003 difference between the outside diameter of the inner tube and the inside diameter of the outer tube. They telescope perfectly before I cut the slots but stick afterwards. There is no problem with burrs so I can only assume that the tubing is being forced out of round by the milling process. Any thoughts on how to true the tubing afterwards or how to prevent this from happening?