G82 / CNC Dwell P-Value Calculator

Inch system. Compute the G82 dwell P value (counterbore / spot-face / flat-bottom) from spindle RPM and the number of flutes.

Unit
Inch (in)
Spindle speed
Tool flutes
Dwell lasts the time for the spindle to turn by one flute spacing (1 / flutes of a revolution), so the next flute reaches the bottom.
Glossary — what do these terms mean?
P (dwell time)
The dwell duration at the bottom of a G82 cycle. The tool feeds down, pauses (dwells) for P, then retracts. The pause lets the cutting edges clean up a flat bottom — important for counterbores, spot-faces, and spot drills. On most Fanuc-style controls P is given in milliseconds with no decimal (P1000 = 1.000 s); some controls take seconds — check your machine.
G82 (drill with dwell)
A canned drilling cycle identical to G81 but with a programmed dwell at the bottom. Used where a clean, flat, burr-free bottom matters more than depth — counterbores, spot-faces, chamfers, and shallow flat-bottom holes.
Dwell time formula
This calculator sizes the dwell so the spindle turns by one flute spacing while paused — long enough for the next flute to sweep the bottom: dwell = (1 / flutes) × 60 / RPM seconds. More flutes or higher RPM → shorter dwell.
Flutes
The cutting edges on the tool. With n flutes, one flute reaches the bottom every 1/n of a revolution, so a dwell of 1/n revolution guarantees a fresh edge passes the bottom once during the pause.
RPM (revolutions per minute)
Spindle speed. Enter it directly, or derive it from surface speed and tool diameter: RPM = (3.82 × SFPM) / D. The dwell is inversely proportional to RPM — a faster spindle needs a shorter pause for the same fraction of a revolution.
Sample G82 program
A minimal dwell-cycle block. The G82 line defines the cycle once — depth Z, retract R, dwell P (ms), and feed F. Each X Y after it repeats the cycle at a new hole until G80 cancels it. 
(--- setup ---)
G00 G90 G17 G20 G40 G49 G80 M05
T10 M06                  (load tool)
G90 G54 S3056 M03        (spindle on, 3056 RPM)
G00 X0.0 Y0.0
G43 H10 Z1.0 M08
G00 Z.1

(--- G82 dwell cycle ---)
G82 G99 Z-.250 R.050 P10 F24.45  (dwell 10 ms at bottom)
X1.0  Y0.0              (cycle repeats at hole 2)
X2.0  Y0.0             (... hole 3)
G80                     (cancel canned cycle)

(--- clean up ---)
G00 Z.1 M09
G28 G91 Z0. M05
G90
M30

Dwell = (1 / flutes) × 60 / RPM, converted up to whole milliseconds for the P word. Verify P against your control's dwell convention before running.