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G74 Left hand tapping cycle / Face groove or peck drill cycle
Centroid CNC12 Acorn G-code · Mill, Lathe
On mills: Left hand tapping cycle
Taps a left hand thread. Start the spindle in M4. At the bottom the spindle reverses using the M codes in parameters 74 and 84.
Format
Addresses
| Address | What it does |
|---|---|
X Y | Hole position |
Z | Hole bottom |
R | R plane |
Q | Thread lead for rigid tapping, needed on every line |
P | Dwell at bottom |
F | Feed for floating tap |
How it works
Modal, canned cycle. Cancel with G80.
Example program
T1 M6 ; LOAD TOOL 1, Z GOES HOME FIRST
G54 G0 X0 Y0 ; WORK OFFSET 1
M4 S500 ; SPINDLE CCW
…
The full 8-line example is in the app. Example is in inch. Check offsets and clearances first.
Watch out for
- With rigid tapping Q is not modal. Put Q on every hole line.
- Feed hold is off in the cycle. Cycle cancel with the tap in the hole will likely break it.
- Program Z a little short of a blind hole bottom. The tap coasts before reversing.
On lathes: Face groove or peck drill cycle
Pecks in Z for face grooving or center drilling. With an X shift and stepover it cuts a face groove wider than the tool.
Verify on your machine. This entry could not be fully checked against the maker manual. Check your machine manual before you run it.
Format
Addresses
| Address | What it does |
|---|---|
R line 1 | Peck retract amount |
X U | Final X shift position |
Z W | Final Z depth |
P | X stepover |
Q | Z peck depth |
R line 2 | X escape amount |
L | Dwell |
How it works
One shot.
Example program
G97 S1000 M3
G0 X0 Z.1 M8 ; START ON CENTER
G74 R.02 ; PECK RETRACT
…
The full 6-line example is in the app. Example is in inch. Check offsets and clearances first.
Watch out for
- For a center drill start at X0 and leave out the X shift and stepover.
- The one line form cannot give the peck retract. It then comes from parameter 73.
- P, Q and D follow the implied decimal rules of parameters 245 and 246. Type a decimal point.
Related codes
G74 on other controls
The same number can mean something different on another control.
| Control | Meaning |
|---|---|
| Fanuc | Left hand tapping cycle |
| Haas NGC | Reverse tapping cycle |
| Mazak (EIA) | Reverse tapping cycle |
| Okuma OSP | Reverse tapping cycle |
| Mitsubishi M70 M80 | Reverse tapping cycle |
| Brother Speedio | Left hand tapping cycle |
| Siemens 840D 828D | Reference point approach |
| Fagor 8055 8065 | Home search |
| LinuxCNC Tormach | Left hand tapping cycle |
| Mach3 Mach4 | Left hand tapping, Mach4 |
| Hurco WinMax (NC) | Left hand tap (ISNC) or single quadrant arc (BNC) |
| Fadal | Left hand tap |
| Swiss (Citizen Star) | Face peck drilling and grooving cycle |
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