href="#ulink_16784b60-d916-5ae8-9cdd-ad5132813dcf">
ON/OFF SWITCHES
The CNC operator can turn a number of switches located on the operation panel to ON state or to OFF state, as necessary to achieve certain operating conditions. These are important switches, used daily, and there are many of them located within the operation panel.
Depending on the controls system (manufacturer’s preferences), these switches can be of two types:
| ▪Toggle switches | ... UP and DOWN |
| ▪Button switches | ... IN and OUT |
Both types work on the same principle - they both select one of two modes available. For example, you flip the switch up or down (for toggle switches), or you push the button once and push it again (for button switches).
Regardless of the switch type, either of the two selections will make the particular switch inactive (OFF) or active (ON) and its function disabled or enabled.
The English word ‘toggle’ means a ‘selection from two opposite options’. A typical household light switch is a good example - it can be either ON or OFF - other options are not possible. In CNC, the operation panel has quite a number of toggle switches, mostly offering a selection from two possible options. Operation panel toggle switches can be similar to a common light switch, at least in the sense that they can be operated by flipping the switch up or down. Toggle switches can also be of the push-button type - push once for ON selection, push once more for OFF selection.
Normally, all toggle/button switches are OFF and activated only as needed. The one exception is the Manual Absolute switch (if available), which should be normally ON. This is a special purpose switch and will be described later in this chapter.
Several toggle switches can be used in combination to achieve a certain desired result, but understanding each switch individually is most important.
In this chapter, the UP/DOWN type of switches will be shown, as they better show their state visually.
Optional Stop
Optional Stop switch is only one of several switches that require a part program input in order to be fully functional. When the miscellaneous function M01 is contained in the part program, the CNC operator may choose to use the Optional Stop switch by setting it to ON position or leave in the normal OFF position.
When the M01 is processed, the program processing will stop. To continue with the program processing, it is necessary to press the Cycle Start button.
Programmers often place M01 function at the end of each tool, with the possible exception of the last tool. It is up to the CNC operator to decide whether to use it or not. There are a number of situations when the Optional Stop switch is useful:
▪Checking tool for wear and other flaws
▪Part dimension check
▪Temporary absence from the machine (see note)
▪... any other activity not required for each part
Leaving machine with Optional Stop set to OFF should be combined with Feedrate Override switch set to zero - always observe safety rules
If the program includes mandatory program stop M00, program processing will always stop - no interference from the operator is necessary.
Single Block
All CNC part programs are always written sequentially, in the order of tasks and instructions needed to complete certain machining operations. Normally, for full production, the Single Block switch is set OFF, so the program processing is continuous. Setting the switch to ON position is useful particularly during setup, as it allows the CNC operator to process one block at a time.
During part setup, using the Single Block mode enables the operator to test not only the program itself, but also settings of tools and offsets, check clearances, depth and width of cuts, and other cutting oriented activities.
Well structured part program always helps during part setup. For example, a common program entry for a tool number three (T03) is:
T03 M06 (NEXT TOOL SEARCH AND TOOL CHANGE)
During single block mode, the next tool search command (T03) will be done first but immediately followed by the actual tool change (M06) - in the same block. There is no pause between the two functions - they will be processed simultaneously as a single block.
There is nothing wrong with the block or program for efficient production, which is always the main objective. On the other hand, the format may slow down the setup in certain cases. Consider a possible scenario that may benefit changing the program structure to two blocks.
If those two functions are programmed in separate blocks, there will be no delay during production, but during setup the two blocks will bring some benefits:
| T03 | (NEXT TOOL READY) |
| M06 | (TOOL CHANGE) |
As the tool search is independent of the actual tool change, it takes place first. Working with Single Block mode set to ON, the CNC operator has the option to walk around the machine, check if the right tool is ready for tool change and - if necessary - make corrections before the ‘wrong’ tool is actually brought into the spindle.
This is only a small example of how program structure may affect setup. Programmer’s cooperation should not be difficult to secure.
Single Block mode is NOT functional for tapping or threading operations
Block Skip
Block Skip switch is another operation panel feature that requires support in the program. Part program that contains a forward slash symbol (
Some controls use description ‘Block Delete’ instead of the more accurate ‘Block Skip’. Keep in mind that no blocks in the program will actually be deleted - they will be only skipped -
