Siemens 828D: Troubleshooting G-Code Tool Changes Guide

On a Siemens 828D, a G-code program can stall during T2 M6 even though the same command works in MDA and ShopMill. The reported sequence is consistent: the spindle reaches the magazine, orients, the magazine rises, and execution stops with “Wait for speed of master spindle SP”. The evidence points to a modal feed-mode conflict inside the machine tool builder’s tool-change subprogram.

Identify the modal-state conflict

The machining program used G95 feed per spindle revolution for drilling. The tool-change subprogram then executed a G01 movement while the spindle was stopped. Under G95, axis feed depends on spindle rotation, so the subprogram waited for master-spindle speed instead of completing the movement.

Apply the program-level workaround

Switch to feed per minute and assign the verified feed value before calling the tool change. Restore feed per revolution afterward only if the following machining operation requires it.

G94 F500
T5 M6
G95

This sequence resolved the reported failure. Keep G94 F500 in a separate block before each affected tool-change block so the required modal state is established before the machine builder’s subprogram begins.

Verify the correction

1. Run the program from a safe restart point before the tool-change sequence.
2. Confirm that G94 is active before execution reaches T5 M6.
3. Verify that the spindle approaches and orients at the magazine, the magazine completes its motion, and the tool exchange finishes without the spindle-speed wait message.
4. After G95 is restored, confirm that subsequent cutting or drilling feed is again interpreted per spindle revolution.

Correct the underlying machine subprogram

The program-level sequence is a workaround for a tool-change subprogram that relies on the caller’s modal feed state. A permanent correction would explicitly establish an appropriate feed mode and feed inside that subprogram before its G01 movement. Because the evidence does not identify the subprogram name, access level, or machine-builder implementation, preserve the working workaround unless the machine builder approves and validates a subprogram change.

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