CNC Control Setup for Milling and Turning:. Peter Smid
M-S-T Lock
The letters M-S-T refer to functions related to machine operation and programmed with three types of corresponding addresses:
| ▪M | ... Machine functions |
| ▪T | ... Tool functions |
| ▪S | ... Spindle functions |
These three function groups represent many physical activities of the machine tool, controlled by the program:
When the M-S-T switch is turned ON, all machine related functions are locked and not available. This setup method allows testing the part program without any tool changes and spindle rotation, although XYZ motions will still be performed. It is often used in Dry Run mode, when there is no part mounted in the fixture.
Z-Axis Neglect - Z-Axis Lock
Another name for the Z-Axis Neglect switch is called the Z-Axis Lock. In either case, the function of this switch is the same. When the Z-Axis Neglect switch is turned ON, and all other switches are OFF, the program can be checked without any motion along the Z-axis, while the rest of the program is processed normally with full functionality.
When using this switch in the ON mode, make sure your ABS (absolute) position is maintained. The initial ABS position should also be available after the Z-Axis Neglect switch has been turned back to OFF, its normal setting.
Machine Lock
This is the ultimate machine lock function. While the M-S-T Lock switch disables mainly non-axis functions of machine operations, and the Z-axis Neglect switch only disables motions along the Z-axis, Machine Lock switch locks all functions and all motions.
When the Machine Lock switch is in the ON position, all machine motions will be disabled, along with any related activities. Locking the CNC machine is often used to verify the part program without actually moving any axes. All other settings should be available for best results of the part verification.
Dry Run
This feature of the Operation Panel is used quite frequently. The subject title ‘Dry Run’ can also be described as saying ‘machining the part dry’. The word ‘dry’ simply means machining without a coolant. As most metal machining will require coolant, the term ‘running the part dry’ is reserved to the program testing stage where there is no part mounted in the fixture, therefore it can be run ‘dry’, as not coolant is required.
A common application of Dry Run is combined with the Z-axis Neglect, when both switches are turned ON. In this case, the Z-axis is locked a short distance above the part, so visually following the toolpath is much easier than if the Z-axis were locked too high, machine zero position included.
Manual Absolute
Older CNC machines had a toggle switch identified as Manual Absolute, with its ON and OFF mode, like other toggle switches. Modern machines only show a status light, but do not provide a toggle switch. The setting ON or OFF can still be made, but through a much more involved method, suing system parameters. That is not to make the CNC operator unhappy - it is for overall safety.
For safety reasons.Manual Absolute mode should always be ON
Manual Absolute is a switch (in whatever form) that updates (if set to ON) or does not update (if set to OFF) the position of the cutting tool when it is moved manually in the middle of program processing. Consider this situation:
Ten holes have to be machined, using drilling fixed cycle mode G81 with G99 command. G81 will drill all ten holes, G99 controls the retract of the drill from each hole to the feed plane level programmed as R-address in the cycle - this is called the R-level. Assume that the R-level is set at 2.5 mm (0.1 inches). When the tenth hole is completed - where exactly is the drill tip point?
Yes, it is at whatever XY drawing location of the tenth hole, but it is also 2.5 mm above the part. This rather short distance prevents the operator to look into the hole and check it, because the drill is in the way. Manual Absolute mode ON comes to the rescue.
By setting the operation mode from Auto to Manual and/or Handle mode (see later explanations), the drill can be moved manually from its current location to a location that allows visual evaluation of the machined hole. of course, the manual motion has changed the programmed XYZ coordinate location. Continuing program processing from this manually reached coordinate location would present serious problems - unless ...
Unless the Manual Absolute mode is turned ON !
Manual Absolute mode ON will update the current coordinate system by the amount of any manual motion performed during program processing
From the example, you can see that Manual Absolute setting being ON makes sense, and setting it OFF does not. For that reason, most controls do not have Manual Absolute function as a toggle switch anymore, just an indicator light.
Auto Power
Not every control system has a special switch that allows a selection between Auto Power ON and OFF. The purpose of this switch is to allow the user an automatic shut-down of the CNC machine, when the control reads the end-of-program function M30. Wire EDM machines often do include this switch, as machining operations are frequently unattended, and may last several hours.
Coolant Function
Coolant function also uses a toggle switch for coolant control, but this switch deviates from the original definition of ‘toggle’, as it has three selectable positions, rather than the normal two.
In the CNC program, coolant (actually coolant pump) is normally turned on by the miscellaneous function M08 and turned off by function M09.
Although the majority of metal machining will require coolant, there are several cases when coolant is either not recommended or not required:
▪For initial program verification (Dry Run mode)
▪For certain materials, such as wood
▪When using ceramic or similar inserts
▪For some hard-machining applications
▪... other reasons
The three-way setting of the Coolant switch provides the following options:
| ▪ON setting | ...Coolant is always enabled |