The required operation is not C-axis indexing. It is simultaneous continuous rotation of the work spindle and the driven tool for center drilling. On the Doosan Puma LM400 with Fanuc Series 21i-T control, the evidence does not identify the enabling M code. Treat that function as machine-builder logic and verify it in the Puma machine manual or through the machine builder's official support channel.
Separate C-axis indexing from dual rotation
A milling-mode sequence that enables the driven tool, references the C axis, positions it at angular coordinates, and applies the spindle brake supports indexed drilling around a diameter. It does not produce continuous work-spindle rotation during drilling. Therefore, a sequence using M76, G28 H0, C-axis positions, M50, and M51 from another Fanuc 21i-T installation does not solve the stated center-drilling requirement.
| Operation | Work spindle | Driven tool | Relevant control behavior |
|---|---|---|---|
| Indexed radial or axial milling | Positioned as a C axis | Rotates | Milling mode, angular positioning, and spindle brake |
| Dual-rotation center drilling | Rotates continuously | Rotates continuously | Machine-specific function must permit and independently command both rotations |
Why an M code from another machine is unsafe
Fanuc executes the CNC program, but machine-tool builders assign many M functions through machine-specific control logic. The evidence gives M76 as milling-mode activation on one Fanuc 21i-T machine and M73 plus M200 on a Biglia machine with Fanuc 31i. It also states that M200 separates the two speed commands on that Biglia installation. None of those assignments establishes the corresponding code for the Doosan Puma LM400.
Do not test these M codes by substitution. An incorrect machine-specific M function can request an unrelated auxiliary action. Locate the Puma M-code table, ladder-function description, training notes, or an archived program known to use simultaneous spindle and driven-tool rotation.
Determine the required relative speed
The intended application is center drilling holes of 1 to 1.5 mm while overcoming a stated work-spindle limit of 2500 rpm. If the work spindle runs at 2500 rpm and the driven tool runs at 1000 rpm in opposite cutting directions, the relative rotational speed is 3500 rpm. If they rotate in the same direction, the relative speed magnitude is 1500 rpm. Confirm the commanded directions before treating the speeds as additive.
Opposite directions: N_relative = |N_work| + |N_tool|
Same direction: N_relative = |N_work - N_tool|The desired function must preserve separate speed commands. Evidence from the Fanuc 31i/Biglia example indicates that, without its machine-specific separation function, the driven tool can follow the speed subsequently commanded for the main spindle. That behavior is not confirmed for the Puma and must be checked rather than assumed.
Verification procedure for the Puma LM400
- Search the machine-builder M-code documentation for simultaneous main-spindle and driven-tool rotation, independent driven-tool speed, or speed-command separation. Do not rely only on the generic Fanuc programming manual.
- Confirm that the function applies to continuous spindle rotation, not C-axis positioning or spindle-brake control.
- Verify which S command addresses each spindle and whether issuing the second speed command overwrites or synchronizes the first.
- Prove the sequence without a cutting load using the machine builder's prescribed safe setup. Observe both commanded speeds and directions, then stop the test if either speed changes when the other spindle starts.
- For the 1 to 1.5 mm center-drilling operation, calculate relative speed from the verified directions and commanded speeds before feeding the tool.
FAQ
Which M code enables dual rotation on a Doosan Puma LM400?
The evidence does not identify it. Use the Puma LM400 machine-specific M-code documentation or the machine builder's official support channel; M76, M73, and M200 are documented here only as assignments from other installations.
Does C-axis milling mode rotate the work spindle continuously?
Not in the indexed-drilling sequence described. That sequence references and positions the C axis at specific angles and applies the spindle brake, while the requested operation requires continuous work-spindle rotation.
Do 2500 rpm and 1000 rpm produce 3500 rpm at the drill?
They produce a 3500 rpm relative speed only when the workpiece and drill rotate in opposite cutting directions. If both rotate in the same direction, the relative speed magnitude is 1500 rpm.