What Your Chips Are Telling You About Your Drill

In machining, chips are the most immediate feedback loop you have. They form at the cutting edge, carry heat away from the cut, and leave evidence of everything that happened during their creation. A machinist who knows how to read chips doesn't have to guess whether the drill is cutting well — the chips say so directly.

Color: The Heat Indicator

Chip color is a proxy for temperature at the cutting zone. In steel:

• Silver/bright: Low temperature. Cutting is clean, heat is being carried away efficiently.
• Straw/gold: Moderate temperature. Normal for many steel alloys at standard speeds.
• Blue/purple: High temperature. Heat is building. Reduce speed, check coolant.
• Black: Very high temperature. The drill is past its cutting edge — it's rubbing and generating heat through friction. Pull the drill immediately and inspect.

For stainless and titanium, even straw-colored chips are worth attention. These materials work-harden rapidly, and elevated temperatures accelerate that process. Bright silver chips are the target.

Shape: The Feed and Geometry Indicator

• Tight curls (C-shaped or 6-shaped): Healthy chip formation. Feed and speed are in the right range.
• Long, stringy chips (ribbon chips): Feed is too low, speed is too high, or the drill has a very high helix angle. In production, ribbon chips wrap around the drill and pack in the flutes. Increase feed or reduce speed to encourage chip breaking.
• Powdery or dusty chips: Feed is too low for the material, or the drill is rubbing rather than cutting. This is the chip signature of a dull drill. A dull cutting edge extrudes and compresses the material, creating fine particles rather than true chips.
• Short, thick chips: Feed is appropriate and the drill is cutting cleanly. Common in harder steels with proper parameters. Desirable — these evacuate easily and carry heat away efficiently.
• Chips with rough or torn edges: The cutting lip geometry is off. A fresh resharpen or geometry inspection is indicated.

Length and Where They Land

Chips should be thrown clear of the drill and land in a reasonable radius around the hole. If chips are collecting around the drill shank or piling up at the entry, they're not evacuating from the flutes — chip packing is starting.

On a CNC machine with flood coolant, watch the coolant drain for chip character. Long, wiry chips in the coolant strainer mean you have a ribbon chip problem. Heavy particulate in the coolant can indicate rubbing — powder that passed through the hole and suspended in the coolant.

Chips After Resharpening

The first five holes after a fresh resharpen are worth paying extra attention to. On a properly resharpened drill, chips should immediately look healthy — clean color, good curl, evacuating well. If the first-hole chips are off-color, powdery, or ribbon-like, the resharpen may have introduced geometry issues or the parameters need adjustment.

This is the practical quality check on any resharpening service: the chips don't lie. A drill that came back from reconditioning and immediately produces healthy chips is a drill that came back right.