Local Machine Service/Repair

Late to the game. . . again. That's me. Am I correct in assuming this is a "round column" mill? When a tube is "struck" by some means, it will tend to spread in a "flat" dimension. Side to side. . . It may, or may not show a dent, depending on how hard it was struck. Just knocked a little out of round. Dropping the column, even in a soft material like sand, can possibly cause the "out of round" condition. I don't know an easy way to find where. You're off to a good start with marking fluid. Swinging side to side may make it more obvious.

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I have an RF30 clone, c.a. 1984. There is a keyway on the left side of the quill to prevent it from rotating. A dog point screw engages that keyway. If the screw in inserted too far, it will cause the quill to bind. An uneven depth of the keyway could cause the binding to occur in some positions and not others.

If your mill is set up similarly, try backing out that screw and see if the binding goes away. If that is the cause of your problem adjust the screw by inserting until binding occurs and slowly back out while checking for free movement. when you reach a setting where you just have free movement throughout the quill travel, back the screw out about 1/8 turn and lock with the jam nut.
 
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