When counter-boring or spot-facing cast iron, what preparatory step is advised?

• A. Polish the surface
• B. Remove the scale with a chisel
• C. Apply oil
• D. Widen the hole

Answer: (B)

Before counter-boring or spot-facing cast iron, you want a clean, true seating surface. Cast iron often has a loose layer of scale on the surface, and if this scale is left in place, it can lift or ride under the tool, causing an inaccurate finish or an out-of-true hole. Removing that scale with a chisel physically knocks off the oxide layer and burrs, giving a flat, solid base for the operation to seat against. This prep helps the tool follow the true surface and maintain correct depth and alignment. Polishing the surface won’t remove the scale, applying oil can contaminate the seating area and affect cutting, and widening the hole changes the feature rather than preparing the surface.