Which statement about cutting speed units is correct?

• A. It is commonly expressed in surface feet per minute (SFM) or meters per minute.
• B. It is always expressed in inches per hour.
• C. It is measured in revolutions per minute only.
• D. It is not related to tool wear.

Answer: (A)

Cutting speed is the velocity of the workpiece surface as it moves past the cutting edge, so it’s expressed as surface speed units like surface feet per minute (SFM) or meters per minute (m/min). These units reflect how fast material at the contact point is being sheared, and they relate to spindle speed and tool diameter through V = πDN (with appropriate unit conversions). The other statements don’t fit: inches per hour isn’t a practical speed unit for cutting speed, revolutions per minute is the spindle speed (not the surface speed), and cutting speed does affect tool wear—higher speeds can increase wear and heat.