M41–M44

Format and notes

M41–M44 (how many ranges there are and which is the low-speed one depends on the machine)

• Switches the spindle's speed-change gear. The low-speed gear gives large torque at low speeds (thick stock, heavy cutting, large threads). The high-speed gear is for high speeds. The MHLW NC lathe training material describes M41–M44 as “setting the gear range (speed range)”
• Many NCs select the gear automatically from the S value, so you usually don't need to write it. M41 and the like are used when you want to fix the gear (Haas, Mitsubishi Electric, Beckhoff)
• Write the gear command together with S before starting the spindle (in the Haas example, M03 comes on the line after S and M41; in the lathe training material example, M41 is written on the tool call line, followed by G97 S_ M03)
• The speed range of each gear is set by machine parameters, and an S outside the range causes an error or an automatic gear change
• Common mistakes: running M43 and M44 from another maker's program as they are (on Haas lathes they unclamp and clamp the turret). Misreading the meaning of M40 (automatic selection on Siemens, gear range 1 on Beckhoff)

Example

T0101 M41 ;        (low-speed gear. On the same line as the tool call)
G97 S300 M03 ;     (set the gear before starting the spindle)

An example written by Kezuriba following the style of the MHLW NC lathe training material.

Most M codes are assigned by the machine builder (the Siemens ISO dialect manual leaves M00–M89 to the machine tool maker). The same number can mean different things on different machines, so always check your machine’s manual.

Differences between controls and machines

The same code can be written or assigned differently depending on the CNC control and the machine builder. Always check your machine’s manual.