G73 and G83 Peck Drilling Cycles — Deep Hole Drilling on CNC Mills

Standard G81 drilling works well for shallow holes, but as depth increases relative to diameter, chips pack into the flutes and the drill overheats, wanders, or breaks. Peck drilling solves this by breaking the cut into incremental passes — either retracting fully to clear chips (G83) or breaking the chip with a short retract (G73).

Choosing between the two comes down to material and hole depth.

G73 — High-Speed Peck (Chip Breaking)

G73 advances the drill by the Q amount, then retracts a small fixed distance (typically 0.1–1mm depending on the controller) before pecking again. The drill never leaves the hole — it just backs off enough to break the chip.

G73 X_ Y_ Z_ R_ Q_ F_

Q — depth of each peck (always a positive value)
R — retract plane above the part
Z — final hole depth
F — feed rate

G73 Example — Ø8mm drill, 40mm deep, aluminum

T3 M6                          (8mm drill)
G0 G90 G54 X30. Y30. S3500 M3
G43 H3 Z50.
M8

G99 G73 Z-40. R3. Q5. F400    (5mm pecks, chip-break retract)
X80. Y30.
X80. Y80.
G80

G0 Z50.
M9 M5
G28 G91 Z0.
M30

Each peck goes 5mm deeper than the last. After reaching Z-40, the drill retracts to R3 and the cycle ends.

Use G73 for: aluminum, brass, and soft materials where chips curl cleanly and break easily. Also used for shorter depth-to-diameter ratios (up to about 3×D).

G83 — Full Retract Peck (Chip Clearing)

G83 is more aggressive about chip evacuation. After each peck, the drill retracts fully to the R-plane, pulling chips out of the hole completely before re-entering. On re-entry, it rapids back to just above the previous depth (typically 1mm above) before resuming feed rate.

G83 X_ Y_ Z_ R_ Q_ F_

The syntax is identical to G73. The difference is entirely in behavior: full retract vs. chip-break retract.

G83 Example — Ø6mm drill, 60mm deep, steel

T4 M6                          (6mm drill)
G0 G90 G54 X50. Y50. S2000 M3
G43 H4 Z50.
M8

G99 G83 Z-60. R3. Q4. F200    (4mm pecks, full retract to R3 each time)
X100. Y50.
X100. Y100.
G80

G0 Z50.
M9 M5
G28 G91 Z0.
M30

Use G83 for: steel, stainless, cast iron, and any material that produces stringy or difficult chips. Also mandatory for deep holes (5×D and beyond) where chip packing is a serious risk.

Choosing Q — Peck Depth

Q should be set based on material and drill diameter. A useful starting point:

Material	Q (relative to drill diameter)
Aluminum	2–5× D per peck
Mild steel	1–2× D per peck
Stainless / hardened	0.5–1× D per peck
Cast iron	1–3× D per peck

For a 6mm drill in steel, 1× D = 6mm per peck. Start conservatively and increase if chip control is good.

The Re-Entry Clearance in G83

When G83 returns to depth after a full retract, it doesn't plunge all the way at rapid — it switches to feed rate at a small clearance distance above the previous depth. This distance is controller-dependent (commonly 1mm on Fanuc) and ensures the drill is cutting at feed rate when it contacts the chips at the bottom, not plunging at rapid into a packed hole.

Some controllers let you set this clearance via a parameter. If you're drilling deep holes in hard material and noticing tool wear at the re-entry point, reducing this clearance (or switching to a slower feed on re-entry) can help.

G73 vs G83 — Quick Reference

	G73	G83
Retract per peck	Short (chip break)	Full (to R-plane)
Chip evacuation	Breaks chip in hole	Pulls chips out
Cycle time	Faster	Slower
Best for	Aluminum, soft materials, 3×D	Steel, deep holes, 5×D+
Re-entry rapid	Not applicable	Yes — returns to near-bottom

Common Mistakes

Q value too large — oversized pecks cause chip packing on the next pass. If the drill stalls or makes unusual noise, reduce Q.

R-plane inside the part — if R is set below the part surface, the drill feeds from the wrong position. Always set R above the surface with clearance for any raised features or weld beads.

Using G73 in deep steel holes — chip breaking doesn't evacuate chips, so deep steel holes with G73 pack up quickly. Switch to G83.

Forgetting G80 — the cycle stays active after the last hole. The next positioning move will trigger another drill cycle. Always cancel with G80.

Simulate Before Drilling

A broken drill inside a 60mm deep hole in hardened steel is a day-ruining event. Before running a new peck drilling program, load it into Eureka3X to verify the R-plane, Z depth, and cycle behavior against the actual part model.

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