📷 IMAGE AREA — Mitsubishi M70 MONITOR screen, CYCLE START / FEED HOLD keys and override dials
Suggested alt text: Mitsubishi M70 MONITOR screen cycle start feed hold and override dials
In this lesson we learn to run a program in NC memory safely: preparing the program to run, switching to AUTO/MEMORY mode, giving CYCLE START, using SINGLE BLOCK, stopping with FEED HOLD, resuming, the effect of RESET and what to do when the program ends.
1. Checks before running
Even if the program is called, CYCLE START is not given immediately. First: is the correct program selected; is the program reset to the start; is the correct tool loaded and is the tool number correct; is the workpiece zero correct; are the tool length/radius offsets correct; is the spindle speed suitable; are the vise/part/clamping elements safe; has the location of the first move been checked; is there an alarm on screen? The Mitsubishi programming manual recommends checking the program, tool offsets and workpiece offsets and doing a dry run before starting actual machining.
2. Resetting the program to the start
If the cursor was left in the middle of the program, the program may not run from the start. So: open the correct program → do TOP SEARCH → check that the cursor is at the start → verify the correct program number on the MONITOR screen. In the example below, if the cursor was left on N60, START must not be given directly — because the tool and spindle commands on N40 and N50 may not have been read.
O1000
N10 G21 G17 G90;
N20 G40 G49 G80;
N30 G54;
N40 T1 M6;
N50 S1500 M3;
N60 G0 X0 Y0;3. Switching to AUTO or MEMORY mode
To run a program in NC memory, the mode switch is set to AUTO or MEMORY (some machines show MEM, some AUTO). Automatic operation cannot start without selecting this mode; the Mitsubishi handbook states that start cannot be given if the automatic operation mode is not selected.
4. Safe settings on the first run (override)
If a new or changed program is run for the first time: Feed Override reduces the cutting feed; on the first run a low value (0–25%) can be selected, but if left at zero the machine does not move — the handbook states that automatic motion can be blocked when the cutting-feed override is zero. Rapid Override reduces the speed of G00 rapids; on the first try a low value like 5%, 10% or 25% is used (if zero, rapid motion cannot start). Single Block runs the program line by line; turning it on for the first run increases safety.
5. What is SINGLE BLOCK?
With SINGLE BLOCK on, the program stops after each line. For example: CYCLE START is given → N10 runs → the program stops → CYCLE START again → N20 runs → the program stops again. This way the operator advances checking each line. The Mitsubishi M700 handbook states that with Single Block active the program stops at the block end and resumes when CYCLE START is given again.
N10 G21 G17 G90;
N20 G54;
N30 T1 M6;
N40 S1500 M3;
N50 G0 X0 Y0;6. Steps to run the program
General sequence: (1) Select the correct program. (2) Reset to the start with TOP SEARCH. (3) Switch to the MONITOR screen. (4) Select AUTO/MEMORY mode. (5) Lower Feed Override. (6) Lower Rapid Override. (7) Turn on SINGLE BLOCK. (8) Close the machine door. (9) Check there is no alarm on screen. (10) Press CYCLE START. When CYCLE START is given, the program starts running.
7. What to watch while the program runs
While the program runs, do not only watch the tool’s motion. On the MONITOR screen, follow: the running program number, the active line/block, the X-Y-Z positions, the active tool number, the spindle speed, the feed rate, the M/S/T commands and any alarms/warnings on screen. On the first run the operator’s hand must be near the FEED HOLD key.
8. What is FEED HOLD?
FEED HOLD temporarily stops the program. If a dangerous or suspicious situation is seen while the program runs, the FEED HOLD key is pressed. Generally: axis motion stops, the program stays active, the cursor is not lost, and the program resumes when CYCLE START is given. The Mitsubishi handbook states that with Feed Hold active the program goes to a wait and can be resumed with CYCLE START.
9. Resuming after FEED HOLD
If the program was stopped with FEED HOLD: check why you stopped it, look at the state of the tool and part, check there is no alarm on screen, verify the mode is still AUTO/MEMORY, and if Feed Override is not at zero give CYCLE START — the program resumes from where it stopped. But if the axes were moved by hand during the stop, resuming directly may not be safe.
10. Stopping and resuming with SINGLE BLOCK
With SINGLE BLOCK on, a normal stop occurs at the end of each block; this is not an alarm. To continue, CYCLE START is pressed again. A stop code such as “T03 Single Block Stop” may appear on screen; in that case the program is resumed by giving CYCLE START.
11. What is RESET?
RESET is not the same as FEED HOLD. RESET usually cancels the program, ends automatic operation, resets some active commands and can return the program execution position to the start. The Mitsubishi handbook states that when a reset signal is given, the program execution position returns to the program start and operation must be run from the beginning. In short: FEED HOLD to pause temporarily, RESET to cancel the program.
12. What to do after RESET?
After pressing RESET, CYCLE START is not given immediately. Sequence: check the spindle has stopped → check the coolant state → check whether the program returned to the start → verify the correct program is active → check the tool number → reset to the start with TOP SEARCH → select AUTO/MEMORY mode → restart with low override values. If the program was interrupted and starting from the beginning is not appropriate, a Program Restart is needed; we will cover this in a separate lesson.
13. What happens if the mode is changed?
If the mode is switched from AUTO to another mode while the program runs, the program may stop. For example an AUTO → JOG change can interrupt automatic operation. The Mitsubishi handbook states that when the operating mode is changed the program stops, and it can be resumed by returning to the old mode and giving CYCLE START. Still, if the axes were moved by hand during the mode change, the position must be checked before resuming.
14. Checks if the program does not run
If the program does not start even though CYCLE START was given: is AUTO/MEMORY mode selected (the program will not run in the wrong mode); is Feed Hold active (the key may be stuck); is Feed Override zero (cutting motion will not start); is Rapid Override zero (G00 may not start); is the RESET signal active (the key may be stuck); are the axes moving; is there an alarm (if NC READY is off, clear the alarm first); is a file write/delete in progress; is a program search in progress? These are explained in the automatic-operation stop codes in the M700 Handbook.
15. What happens at the program end? (M30)
At the end of the main program there is usually M30. When M30 runs, generally: the program ends, axis motion stops, the program returns to the start and the control becomes ready to run again. But by the builder’s PLC structure the behavior of coolant, spindle or auxiliary systems can vary. After the program ends, check: has the spindle stopped, has the coolant turned off, is the tool in a safe position, has the program returned to the start, is there an alarm on screen?
16. Running the program a second time
If another part will be machined: check that the program returned to the start, check that the new part is clamped correctly, make sure the workpiece zero has not changed, check that the tool is not broken/worn, and give CYCLE START. If the program did not return to the start after M30, TOP SEARCH must be done.
17. Recommended method for the first run
The safest sequence for the first try of a new program: (1) Reset the program to the start. (2) Switch to AUTO/MEMORY mode. (3) Turn on SINGLE BLOCK. (4) Lower Feed Override. (5) Lower Rapid Override. (6) Keep the tool at a safe distance from the part. (7) Give CYCLE START. (8) Check the motion after each line. (9) Use FEED HOLD if needed. (10) Turn off SINGLE BLOCK once the program is seen to be safe.
18. Difference between FEED HOLD, RESET and EMERGENCY STOP
| Key | Purpose |
|---|---|
| FEED HOLD | Temporarily stops the program |
| CYCLE START | Starts or resumes the program |
| RESET | Cancels the program or resets the control |
| EMERGENCY STOP | Stops the machine in a real danger |
Emergency Stop must not be used as a normal program-stop key; but if there is a collision risk or serious danger, it must be used without hesitation.
Lesson summary
In this lesson we learned the checks before running a program, switching to AUTO/MEMORY mode, starting the program with CYCLE START, running line by line with SINGLE BLOCK, stopping temporarily with FEED HOLD, resuming with CYCLE START, that RESET can cancel the program, and the checks to do at the program end.
Next lesson — Lesson 5: Calling a program from a CF card and USB memory (selecting the external device, finding the program on the card/USB, copying it to NC memory, what to do if the same program number exists, whether direct running from an external device is possible, and cautions when removing the card/USB).
📷 IMAGE AREA — Running line by line with SINGLE BLOCK and the difference between FEED HOLD / RESET / EMERGENCY STOP
Suggested alt text: Mitsubishi M70 single block feed hold reset and emergency stop usage