This section is from the book "The Boy Mechanic Vol. 2 1000 Things for Boys to Do", by Popular Mechanics Co.. Also available from Amazon: The Boy Mechanic, Vol2: 1000 Things for Boys to Do.
Reducing the diameter of a small rod by filing while it is turning in a lathe is a difficult thing to do, as the pressure of the file on one side bends the rod. The filing may be easily accomplished by using two files, as shown in the sketch. In this manner almost any amount of pressure can be applied by the Rod from Bending squeezing the files together without danger of bending the rod. - Contributed by J. F. Tholl, Detroit, Mich.