What is the limiting factor for how fast a drill or endmill can feed through any material?

• A. Maximum speed of machine spindle
• B. Operator courage
• C. Phase of the moon at that particular hour
• D. Size / strength of cutting edges/ lips

Answer: (D)

The limiting factor is the cutting edge itself—the size and strength of the lips. The edge has to shear and carve away material, and its geometry and toughness determine how much chip load per tooth it can safely carry. If you push the feed too fast, the edge can dull, chip, or fail, and cutting becomes rubbing with excessive heat, leading to poor finishes or breakage. You can trade speed for a higher spindle RPM or adjust the feed to maintain an allowable chip load, but you cannot exceed what the edge can handle. The other factors listed don’t set the fundamental limit in practice; the edge’s capability governs how fast you can effectively and safely move through material.