📷 IMAGE AREA — FEED HOLD, CYCLE START, RESET and EMERGENCY STOP keys on the Mitsubishi M70 panel
Suggested alt text: Mitsubishi M70 feed hold cycle start reset and emergency stop keys
In this lesson we learn which stopping method to use in which situation while a program runs: temporary stop with FEED HOLD, SINGLE BLOCK stop, M00 and M01 stops, cancel with RESET, restarting the program from the beginning, and when to resume from where it stopped vs start over.
1. Why is a program stopped?
A program can be stopped for: tool/part checking, dimensional checking, a suspicious move, chip cleaning, tool wear, a program error, an alarm, a power failure or an emergency. The same key is not used for every stop. The most important distinction: temporary stop → FEED HOLD, cancel the program → RESET, real danger → EMERGENCY STOP.
2. Temporary stop with FEED HOLD
FEED HOLD is used to stop the program temporarily. General operation: press FEED HOLD while the program runs → wait for the axes to stop → check the program stays active → if there is no problem, resume with CYCLE START. The Mitsubishi handbook states that with Feed Hold active the program stops and can be resumed with CYCLE START. During FEED HOLD: the program is not cancelled, the cursor stays around the current block, the mode should not be changed, the axes should not be moved by hand, RESET should not be given. If the axes are moved by hand, resuming from where it stopped may not be safe.
3. SINGLE BLOCK stop
With SINGLE BLOCK on, the program stops at the end of each line; after each line, CYCLE START is given to move to the next line. This stop is not an alarm. The Mitsubishi handbook explains that with Single Block on the program stops at the block end and resumes when CYCLE START is given again.
N10 G21;
N20 G54;
N30 T1 M6;
N40 S1500 M3;4. M00 program stop
M00 is the compulsory stop command written into the program (e.g. N50 M00;). When the program reaches this line it stops; use cases: checking the part, cleaning chips, doing a manual operation, seeing the tool/part position. To continue: do the needed check, verify the door is closed, check there is no alarm and give CYCLE START. When M00 runs, it does not matter whether the Optional Stop switch is on or off.
5. M01 program stop
M01 is the optional stop command (e.g. N60 M01;). M01 stops the program only when the OPTIONAL STOP switch on the panel is on; when the switch is off, the program passes the M01 line and continues. M01 is usually used in first-part checking, between certain operations and when operator control is needed.
6. Cancelling the program with RESET
RESET does not stop the program temporarily; in most cases it cancels program execution. After RESET: the program may return to the start, the current block position may be lost, some active modal commands may change, and resuming directly from where it stopped may not be possible. The Mitsubishi handbook states that when reset is given, the program execution position returns to the program start and the program must be run from the beginning. So if you want to stop only for a check, use FEED HOLD.
7. START is not given immediately after RESET
After RESET, these must be checked: has the spindle stopped, has the coolant turned off, where is the tool, has the program returned to the start, is the correct program active, is there an alarm on screen, is there a safe distance between the tool and the workpiece? Giving CYCLE START directly after RESET can be dangerous.
8. Restarting the program from the beginning
General sequence: (1) Give RESET. (2) Check the program has fully stopped. (3) Reselect the correct program. (4) Do TOP SEARCH. (5) Check the cursor is at the program start. (6) Switch to AUTO/MEMORY mode. (7) Lower Feed and Rapid Override. (8) Turn on SINGLE BLOCK. (9) Give CYCLE START. Re-reading the preparation commands at the program start is important. For example if the program below is started only from N60, G54 may not be selected, the tool may not be called, the spindle may not be turning or the compensation commands may not be correct; so in a normal case the program is run from the beginning.
O1000
N10 G21 G17 G90;
N20 G40 G49 G80;
N30 G54;
N40 T1 M6;
N50 S1500 M3;
N60 G0 X0 Y0;9. Situations where you can resume from where it stopped
Generally you can resume with CYCLE START in these cases: stopped with FEED HOLD, stopped at a SINGLE BLOCK end, stopped with M00, stopped with M01, the mode changed briefly but the axes were not moved. The Mitsubishi handbook states that in Feed Hold and Single Block stops you can resume with CYCLE START.
10. Situations that require starting from the beginning
Generally the program must be restarted from the beginning in these cases: RESET was given, the wrong program was selected, the program was changed, the tool or coordinate information was changed, the axes were moved by hand to a different position, it is not clear where the program stopped, the DNC connection dropped, or the program file was reloaded. Starting the program from a random point in the middle is not safe.
11. Situations that need a Program Restart
In these cases a Program Restart may be needed instead of starting over: a power failure, a broken tool, Emergency Stop used, the program accidentally reset, the program interrupted by operator intervention, or when you do not want to run a long mold program from the start again. The M70 Program Restart document explains that in these cases the program can be restarted from where it stopped with Type 1 or Type 2. This topic is covered in detail in a separate lesson (Lesson 9).
12. What to do when an alarm occurs
If the program stopped due to an alarm: read the alarm number and message, check which block the alarm occurred in, do not give RESET immediately, note the line where the program stopped, check the tool and axis positions, clear the alarm cause, and decide whether to resume, restart or start over. Giving RESET without seeing the alarm can make it harder to determine where the program stopped.
13. Emergency stop (EMERGENCY STOP)
EMERGENCY STOP must be used only in a real danger: collision risk, the tool going toward the part in the wrong direction, the part coming out of the clamping, abnormal motion in the spindle/axes, or operator safety being at risk. After Emergency Stop the program is not resumed directly; first the danger is removed, the axis and tool position is checked, the machine is made ready again, and whether the program will be run from the start or with a restart is determined. The Program Restart source states that programs interrupted by Emergency Stop can be resumed with the restart function.
14. Comparison of stopping methods
| Stop method | Does the program stay active? | Resume method |
|---|---|---|
| FEED HOLD | Usually yes | CYCLE START |
| SINGLE BLOCK | Yes | CYCLE START |
| M00 | Yes | CYCLE START |
| M01 | Yes | CYCLE START |
| RESET | Usually cancelled | From the start or Restart |
| EMERGENCY STOP | Operation is interrupted | After checking, from the start or Restart |
15. Moving the axes by hand during a stop
Even if the program is stopped with FEED HOLD, moving the axes with JOG or HANDLE changes the situation. For example if the tool was moved away from the program position, CYCLE START must not be given directly; because the program may continue the cutting move it was on, take the tool quickly to the old position, and hit the part or a clamping element. If the axes were moved by hand: stop the program, check the current position, use Program Restart if needed, create a safe return position, and test with low override.
16. What to do if the tool was changed
If the program stopped midway and the tool was changed, do not continue directly. These are checked: the correct tool number, tool length offset, tool radius offset, spindle speed, spindle direction, coolant command and the tool’s position in the program. In Program Restart Type 1, checking the past M, S, T and B commands from the MSTB History screen is recommended.
17. Program reset to start but the tool is near the part
Even if the program will be run from the beginning, the tool may be near the part or in a cut. In that case: move the tool to a safe Z position, check the part and clamping elements, examine the program’s first rapid move, lower Rapid Override, turn on SINGLE BLOCK, and watch the first moves carefully. Resetting the program to the start does not mean the machine is physically in a safe position.
18. Decision table for beginners
- I want to stop only for a check: FEED HOLD.
- The program stopped at M00 or M01: check → CYCLE START.
- I want to cancel the program completely: RESET.
- I gave RESET and will start over: select the program → TOP SEARCH → AUTO → CYCLE START.
- The program is long and stopped midway: use the Program Restart procedure.
- There is a collision risk: EMERGENCY STOP.
19. Short application example and lesson summary
Stopping for a tool check: press FEED HOLD → wait for the axes to stop → check the tool/part → do not touch the axes by hand → check there is no alarm → verify the AUTO/MEMORY mode has not changed → resume with CYCLE START. Restarting the program from the beginning: press RESET → check the machine has stopped → select the correct program → TOP SEARCH → check the program start → lower Feed and Rapid Override → turn on SINGLE BLOCK → select AUTO/MEMORY → give CYCLE START. In this lesson we learned temporary stop with FEED HOLD, the SINGLE BLOCK stop, the M00/M01 difference, that RESET can cancel the program, resetting to the start with TOP SEARCH, when to resume vs start over, and the situations that need a Program Restart.
Next lesson — Lesson 9: Restarting an interrupted program with Program Restart Type 1 (when Type 1 is used, MONITOR → RESEARCH → TYPE 1, Restart Search, MSTB History, checking tool/speed/coolant commands, a safe axis position and restarting with low override).
📷 IMAGE AREA — Stopping-method decision chart: FEED HOLD / M00-M01 / RESET / EMERGENCY STOP
Suggested alt text: Mitsubishi M70 stopping methods feed hold m00 m01 reset emergency stop decision chart