A machine shaft and bore should always be checked for out-of-round status before performing which task?

• A. Pressing a bearing
• B. Shaft alignment
• C. Lubricating bearings
• D. Measuring runout

Answer: (A)

Checking for out-of-roundness before pressing a bearing is essential because a press-fit relies on perfectly concentric surfaces. If the shaft or bore isn’t truly round, the bearing will not seat evenly during pressing, causing binding, uneven contact, and high localized stresses that can deform parts, misalign the bearing, or damage the bearing race. By verifying runout first, you ensure the surfaces are within tolerance so the bearing can be pressed on smoothly and seat true, delivering a reliable, concentric fit.

Lubricating bearings or measuring runout are separate steps in the process, and shaft alignment is a different operation that benefits from a true, correctly seated bearing but hinges on the same principle: avoid introducing a misfit during the press.