After machining it is sometimes useful to file the workpiece while it is held in the lathe. This can be accomplished using the "free-hand" method or by using a guide. 

The below photographs show a guide that I made which provides more precision than the free-hand method.  The guide is positioned in the cross-slide and includes an up/down adjustment, useful for accurate setting of the depth of filing. The file itself rests on rollers which include shoulders to protect against the file contacting the jaws of the chuck.