Lathe centers may need readjusting during a job because of

• A. Expansion
• B. Contraction
• C. Wear
• D. Thermal lag

Answer: (A)

When you’re turning, heat is generated in the workpiece and the machine parts. Metals expand as they heat, so the distance between the centers tends to increase during a job. That growth shifts the centers out of exact alignment, which can throw the work off true on the centerline. To maintain accuracy, you recheck and reposition the centers to compensate for this expansion.

Contraction would occur if things cooled, which isn’t the typical condition during a cut. Wear can cause gradual drift, but the immediate need to readjust during a job is usually due to thermal expansion from the heat of cutting. Thermal lag describes a delay in temperature change, not the primary reason centers need moving to stay in alignment.