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FIGURE 13-Directions of Feed and Cut showing (A) Turning work between centers and (B) Facing off a work piece.

In normal machining, the depth of cut is set by the crosslide handwheel, and the feed is provided by the handwheel on the end of the bed. When facing off the end of a work piece held in a chuck or faceplate, the depth of cut is set by the handwheel on the end of the bed, and the feed is provided by the crosslide handwheel. (See Figure 13B above.)

When using a mill, cut is determined by the amount of depth the cutter is set to by the "Z" axis handwheel. Feed is supplied by either or both the "X" or "Y" axis handwheels depending on the desired direction of the cut.

General rules for feed rates and cutting speeds

Before attempting to machine any metal, please try to remember this simple rule about machining:

"If the tool chatters, decrease speed and increase feed."

Understanding this simple rule can save you many hours of grief. When the tool "chatters", it is not cutting in a continuous fashion. Metal likes to be machined in a way that allows the material to come off in a continuous strip while the tool is in contact with the metal. If the tool is not fed at a rate that is fast enough, the tool skips along the surface, occasionally digging in. The surface of the tool that is doing the most cutting will find a frequency of vibration that is a product of all the variables involved. This can cause anything from a high pitched whine on light, high speed cuts to a resonating racket that can rip the work out of the chuck on heavy cuts. If you maintain the same feed rate and reduce the RPM, the feed will increase because chip will be thicker. (If that sounds wrong at first, think of it this way: At the same feed rate, if you cut the RPM in half, twice as much metal must be removed with each rotation to get to the end of the cut in the same amount of time. The chip is twice as thick, so the feed is GREATER at lower RPM if the feed RATE stays constant.)

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