Holemaking and tapping
Peck drilling calculator
Start at a first peck of 1 x D and later pecks of 0.5 x D (rule of thumb); a 0.2500 in drill to 1.5000 in deep takes 11 pecks.
Technical review pending. Formulas and values are cited. This notice comes down after a machinist review.
Number of pecks
pecks
pecks = 1 + ceil((Z - first) / later) = 1 + ceil((1.5 - 0.2500) / 0.1250) = 11
First peck 0.2500 in (1 x D), later pecks 0.1250 in (0.5 x D). Starting point; adjust by chip form and spindle load. Depth is 6.0 x D.
G83 Q value
Fanuc-style mill: G83 G99 Z-1.5000 R_ Q0.1250 F_
Q is the later peck, incremental and positive. With one Q value every peck is Q deep: 12 pecks to 1.5000 in. R_ is your retract plane and F_ your feed.
Source: peck ratios are shop rules of thumb, not a standard; G83 format from control programming manuals (Fanuc-style mill controls).
How it works
pecks = 1 + ceil((Z - first) / later)
| Symbol | Meaning | Unit |
|---|---|---|
| Z | Programmed hole depth | in or mm |
| first | First peck depth = k1 x D | in or mm |
| later | Later peck depth = k2 x D; this is the G83 Q value | in or mm |
| D | Drill diameter | in or mm |
| k1, k2 | Peck ratios, rule of thumb 1.0 and 0.5 | x D |
| ceil | Round up to the next whole peck | none |
When the first peck already reaches Z, the hole takes 1 peck. On a Fanuc-style mill the cycle is G83 X_ Y_ Z_ R_ Q_ F_, with Q as the peck depth: incremental, positive, no sign.
Worked example: 1/4 in drill, 1.5000 in deep
A 0.2500 in drill to Z 1.5000 in, first peck 1.0 x D, later pecks 0.5 x D.
- First peck: 1.0 x 0.2500 = 0.2500 in.
- Later pecks: 0.5 x 0.2500 = 0.1250 in.
- Depth left after the first peck: 1.5000 - 0.2500 = 1.2500 in.
- Pecks: 1 + ceil(1.2500 / 0.1250) = 1 + 10 = 11.
- Block, single-Q form on a Fanuc-style mill: G83 G99 Z-1.5000 R0.1000 Q0.1250 F_ (R plane is an example).
Result: 11 pecks with the split, Q0.1250. A single-Q block pecks 0.1250 in each time: 12 pecks.
Worked example: 10 mm drill, 50 mm deep
A 10 mm drill to 50 mm, first peck 1.0 x D, later pecks 0.5 x D.
- First peck: 1.0 x 10.000 = 10.000 mm. Later pecks: 0.5 x 10.000 = 5.000 mm.
- Depth left: 50.000 - 10.000 = 40.000 mm.
- Pecks: 1 + ceil(40.000 / 5.000) = 1 + 8 = 9.
Result: 9 pecks, Q5.000 in mm.
Shop notes
- Rule of thumb: peck when the depth passes about 3 x D. Treat every ratio here as a starting point.
- Rule of thumb: G73 (chip break, short retract) for moderate depth, G83 (full retract) for deep holes.
- Reduce the peck depth in gummy materials; adjust by chip form and spindle load.
- Tool-maker data for coolant-through carbide drills overrides these ratios.
- Full-diameter depth: add the tip length. A 0.2500 in, 118° drill to 1.5000 in full diameter programs to 1.5000 + 0.0751 = 1.5751 in.
- No feeds or speeds here; the spindle speed calculator covers RPM from the tool maker's SFM (surface feet per minute).
FAQ
How deep can you drill before you need to peck?
Rule of thumb: past about 3 x D. Coolant-through carbide drills follow the tool maker's data instead.
What Q value for a 1/4 in drill?
0.1250 in at the 0.5 x D rule of thumb.
G73 or G83?
G73 breaks the chip with a short retract; G83 retracts fully to clear chips in deep holes. On a Fanuc-style mill both take the peck depth as Q.
How many pecks for a 10 mm drill 50 mm deep?
9, at a 10.000 mm first peck and 5.000 mm pecks after that.
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