Feeds and Speeds for Turning

Speeds and feeds are critical factors in the performance of a lathe and the quality of the parts being produced. Proper selection of speeds and feeds can optimize tool life, surface finish, and dimensional accuracy.

• The speed of the lathe spindle and the feed rate of the tool against the workpiece all affect tool performance. The cutting speed is the speed at which the tool is moving relative to the workpiece. The feed rate is the distance that the tool advances per revolution of the workpiece. Other variables that affect tool performance include the material being machined, the tool geometry, the tool material, and the depth/width of cut.

• In addition to these variables, the type of turning operation being performed also affects the ideal speed & feed needed to create a quality cut

Formulas can be used to get "in the ballpark" of where your speeds and feeds should be when performing turning operations, but beyond that you also want to learn how to use your senses (see, feel, hear) to identify if a cut is performing as expected:

• SEE: Observe the cutting tool and the workpiece to ensure that the tool is making the desired cut and that the workpiece is being properly shaped. For example, a machinist might look for signs of chatter, such as tool marks or uneven surfaces, and adjust the cutting speed and feed rate accordingly. Additional, chip color, size, and shape provides good indicators of cutting performance

• FEEL: Use your sense of touch to determine whether a cut is performing as expected. By feeling the vibrations of the lathe during cutting operations, you can feel if the cut is smooth and consistent vs. chatter-y, as well as if the tool is feeding as the rate it wants to vs. being aggressively forced into the part.

• HEAR: Use your sense of hearing to detect any unusual sounds coming from the lathe or cutting tool. If the tool is making a high-pitched squeal, it typically indicates the speed is too high, feed is too low, and/or the tool is too dull. If you hear a grinding sound, it typically indicates the speed is too low, feed is too high, and/or the tool is chipped/broken/dull.