If you've ever drilled a deep hole and ended up with a wadded-up bird's nest of stringy chips jammed in the flutes — or worse, a broken bit buried in your workpiece — you skipped peck drilling when you shouldn't have. It's one of those techniques that feels like extra work until the day it saves your part.
Peck drilling is a technique where you advance the drill a set depth, retract it fully or partially to clear chips, then re-enter and advance further. You repeat this cycle until you hit full depth. Instead of plunging straight through in one continuous pass, you're breaking the cut into smaller bites. The retract stroke pulls chips out of the hole before they pack, overheat, or drag back through the cutting edge on re-entry.
Deep holes — generally deeper than 3x diameter. Once you exceed 3 diameters of depth in a single pass, chips start packing against the lands and the wall of the hole. You'll feel it as increased torque. Ignore it long enough and the bit snaps at the flute.
Stringy materials. Aluminum, low-carbon steel, copper, and brass all produce long, continuous chips. In a deep hole with no peck cycles, they spiral around the drill body and generate friction heat that kills the cutting edge fast.
Blind holes where chip evacuation matters. Through-holes have an exit. Blind holes trap everything. In a blind hole past 2x diameter, pecking isn't optional if you want a clean, on-size hole.
Thin or fragile workpieces. Stringy chip tangles create side loads. On thin-wall parts or unsupported workpieces, that lateral force will shift the part before you know what hit you.
Full peck (G83 in G-code): The drill retracts all the way to the R-plane on every cycle. This fully clears chips from the hole. It's slower. For deep holes in stainless, titanium, or stringy aluminum, it's worth every second.
Partial peck / chip-breaking (G73 in G-code): The drill retracts only a small amount — typically 0.010–0.040" — on each cycle. This breaks the chip without fully clearing it from the hole. Much faster cycle time, works well in cast iron, short-chip materials, and moderate-depth holes. It does not give you chip evacuation; it just prevents continuous chip curl.
The rule of thumb: if the material produces long stringy chips, use full peck. If it produces short brittle chips (cast iron, free-machining steel), partial peck is usually enough.
Set your depth stop to your peck increment. A good starting point is 1x diameter per peck for typical jobs — so a 1/2" drill pecks 1/2" at a time. For difficult materials or deep holes, go shallower: 1/2 diameter or less.
Drill to the stop, retract until you feel the flutes clear the hole entrance, advance again. In stringy materials, pull fully out, brush or blow chips away, then re-enter.
One thing manual drillers miss: re-entry speed. Don't plunge back in fast. Feed in at your normal drill rate — plunging fast on re-entry pushes chips down ahead of the point and defeats the whole purpose of the retract.
Chips that re-enter the cut act like grinding compound. They drag across the cutting lips, heat up the margins, abrade the web. Regular peck cycles mean chips are gone before they can do damage. The bit runs cooler. In practice, properly pecked holes extend bit life by 30–50% in deep-hole applications.
| Depth-to-Diameter Ratio | Material | Peck Type | Increment |
|---|---|---|---|
| 3–5x | Free-machining steel | Partial peck | 1.5x dia |
| 3–5x | Aluminum | Full peck | 1x dia |
| 5–8x | Any steel | Full peck | 1x dia |
| 5–8x | Stainless, titanium | Full peck | 0.5x dia |
| >8x | Any | Full peck | 0.5x dia or less |
These are starting points, not law. Watch your chips. Short, tightly curled chips mean your increment is fine. Long stringy chips packing in the hole mean back off.
A sharp drill with correct geometry evacuates chips more efficiently than a dull one. Dull bits require more peck cycles at shorter increments to do what a sharp bit does naturally. If you're fighting chips constantly on holes that shouldn't be a problem, inspect the cutting edges first.
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