CNC Training

What does a M05 code do?

The M05 code turns the spindle off.

M05 cancels any spindle rotation that has been set with either the M03 code (clockwise spindle rotation) or M04 code (counterclockwise spindle rotation).

Which codes are used to turn the spindle on?

There are two codes for turning the CNC spindle on.

M03 turns it on in a clockwise direction. M03 is used with right hand tooling.

M04 turns it on in a counterclockwise direction. M04 used with left hand tooling.

If you need to change directions, then it is best to stop the spindle before changing directions.

M5 vs M05

Some people get confused about whether the 0 is required to include with an M05 code.

To clear this up, there is no need to include the zero in the code. 

The CNC machine will read the code the same. It really is just a matter of preference.

Often you will see the full M05 code used in textbooks or other reference materials. In practice though, many prefer the shortened M5 code in their programs.

If you are working on your own, then go with whichever format you prefer. 

If you work in a bigger shop, make sure to stick to the format that the business has been using.

What other codes will stop the spindle?

There are multiple codes that turn the spindle off. 

Most of them perform multiple functions such as stopping various machine functions all at once. Some of those codes are:

• M00 – Program stop
• M01 – Optional stop
• M02 – Program end, no rewind
• M30 – Program end with rewind

M00 and M01 are both stops.

They both will turn off the spindle, turn off the coolant, stop any machine movement and pause your program until the cycle start button is pushed again. 

The difference between the two is that M00 will always cause the machine to act in this way and M01 will only cause the CNC to perform these action if the optional stop switch or button is set to on.

M02 and M30 are both program end codes. 

They will cause the machine to shut everything down just like the M00 and M01 codes but instead of pausing the program, they stop it.

M02 is a legacy code from when many CNC programs were made on tape for the machine to read. The M02 code would cause the machine to end the program. 

The M30 command would end the program and then rewind the tape back to the beginning of the program.

In many newer CNC machines, the M02 code is treated the same as the M30 code. In cases where the default is not to treat the codes the same, the machine often has a setting that can allow it to treat them both as M30 codes.

M02 codes are not needed on newer CNC machines. M30 is the standard code to end a CNC program.

What does a M06 code do?

The M06 code tells the CNC to perform a tool change.

The machine will swap the tool that is in the ready position of the automatic tool changer into the spindle.

Preparing the CNC for a tool change

You should be aware of some of the characteristics of your cutting tool. The size, as in diameter and length need to be taken into account.

A cutter with a very large diameter may need to be placed near empty spots in your tool changer so it doesn’t smash into other tools.

Length isn’t usually as big of an issue but still keep it in mind to make sure you have enough clearance with the machine and with your part.

Another big thing to consider is the weight of the cutter. Check your machine manual because the capabilities of various machines differ. 

Remember that the total weight of everything you are putting in the spindle or automatic tool changer is what counts, not just the cutter.

Executing a tool change

Certain conditions need to be met for a safe tool change.

Machine movement needs to be stopped and the machine should be in the tool change position. Often this position is the same as the home position.

The spindle should be stopped and the tool to be swapped in should be in the ready position.

Performing a tool change without an automatic tool changer

If your machine doesn’t have an automatic tool changer, then the operator (probably you) will need to change the tools manually.

The best way to do this is to put a program stop in your program using the M00 code. You should include comments in your program at the program stop to tell the operator what they are expected to do.

What other CNC codes are used with the M06 command?

The main code used with the M06 command is the T code.

The T code selects the tool that will be swapped in.

The line of code performing the tool change will usually be something like:

T02 M06

In this example tool #2 is readied for the tool change and then the M06 tells the CNC to swap the tool into the spindle.

M6 vs M06

Some people get confused about whether the 0 is required to include with an M06 code.

To clear this up, there is no need to include the zero in the code. 

The CNC machine will read the code the same. It really is just a matter of preference.

Often you will see the full M06 code used in textbooks or other reference materials. In practice though, many prefer the shortened M6 code in their programs.

If you are working on your own, then go with whichever format you prefer.

If you work in a bigger shop, make sure to stick to the format that the business has been using.

Frequently asked questions about the M06 code

Do you use the M06 code if you want to switch to an empty spindle?

Yes, just call up a tool holder location without a tool in it. 

When the M06 command is used the machine will swap in the empty spot, leaving no tool in the spindle.

Do you need to use the M06 command if you don’t have an automatic tool changer?

No, if you don’t have an automatic tool changer, the M06 code isn’t needed.

Without an automatic tool changer all tool changes will need to be done manually.

M07 is a modal command which turns on mist coolant.

Mist coolant is compressed air and coolant (usually oil). 

It can be more efficient than flood coolant and in some situations be better at clearing chips than flood coolant, but it is used far less often than flood coolant with the M08 command.

M07 [mist coolant] vs M08 [flood coolant]

The most common type of coolant used in CNC machining is flood coolant using the M08 code.

Flood coolant is where the cutter and workpiece are literally flooded with the coolant fluid. This works to lubricate the part, remove chips, and reduce heat buildup.

Mist coolant with the M07 code combines the coolant fluid with compressed air and sprays it on the cutting area.

Mist coolant uses less coolant fluid and can be less messy depending on your CNC setup, but it isn’t as good at reducing heat buildup as flood coolant is.

Advantages of using coolant

The three main advantages of using coolant with your CNC machine are:

• Lubricate the cutter
• Clear chips
• Reduce heat buildup

What are the other options for using coolant?

We discussed mist and flood coolant above but there are other options available as well including:

• Air: This type of coolant reduces heat and clears the chips, but it does not lubricate the workpiece. This type of coolant is used more often with sensitive materials.
• High pressure: High pressure coolant is similar to flood coolant. The only difference is that it hits the workpiece at greater than 1000psi. The higher pressure and higher quantity of coolant helps cool the cutter better and remove more chips.
• Through spindle: Through spindle coolant delivers the coolant directly where it is needed. It is better at clearing chips in many cases because the coolant from the spindle pushes the chips out of a hole or pocket.

How to turn off coolant

The M-code to turn coolant off is M09.

However, there are other stopping commands that also turn off coolant as part of their function including:

• M00 – Program stop
• M01 – Optional Stop
• M02 – Program end, no rewind
• M30 – Program end with rewind

Frequently asked questions about the M07 code

Does every CNC machine have coolant capabilities?

Yes and no.

You can expect that all industrial level CNC machines will have coolant capabilities.

Home or hobbyist level machines such as CNC routers often do not have coolant capabilities, but they can usually be added on if needed.

M08 is a modal command which turns on flood coolant.

Flood coolant is literally flooding or washing the cutter and/or workpiece in liquid coolant. The coolant helps remove chips from the cutting area.

If chips are not moved from the cutting area, then they can end up being recut which tends to cause heat buildup and can damage your cutting tool.

Flood coolant also cools the cutter and workpiece and lubricates the cutter. 

Both of these things help extend the life of your cutter as well.

M08 [flood coolant] vs M07 [mist coolant]

The most common type of coolant used in CNC machining is flood coolant with the M08 code.

The second most common option is mist coolant using the M07 code.

Mist coolant combines the coolant fluid with compressed air and sprays it on the cutting area. 

Mist coolant uses less coolant fluid and can be less messy depending on your CNC setup, but it isn’t as good at reducing heat buildup as flood coolant is.

Advantages of using coolant

The three main advantages of using coolant with your CNC machine are:

• Lubricate the cutter
• Clear chips
• Reduce heat buildup

What are the other options for using coolant?

We discussed mist and flood coolant above but there are other options available as well including:

• Air: This type of coolant reduces heat and clears the chips, but it does not lubricate the workpiece. This type of coolant is used more often with sensitive materials.
• High pressure: High pressure coolant is similar to flood coolant. The only difference is that it hits the workpiece at greater than 1000psi. The higher pressure and higher quantity of coolant helps cool the cutter better and remove more chips.
• Through spindle: Through spindle coolant delivers the coolant directly where it is needed. It is better at clearing chips in many cases because the coolant from the spindle pushes the chips out of a hole or pocket.

How to turn off coolant

The M-code to turn coolant off is M09.

However, there are other commands that turn off coolant as part of their function including:

• M00 – Program stop
• M01 – Optional Stop
• M02 – Program end, no rewind
• M30 – Program end with rewind

Frequently asked questions about the M08 code

Does every CNC machine have coolant capabilities?

Yes and no.

You can expect that industrial level CNC machines will have coolant capabilities.

Home or hobbyist level machines such as CNC routers often do not have coolant capabilities, but they can usually be added on if needed.

The M09 M-code turns off the CNC machine’s mist and flood coolant functions.

This shuts off the “normal” coolant flow.

Other types of coolant, such as through spindle coolant, usually have their own code for turning the specialized coolant functions on and off.

Advantages of using coolant

The three main advantages of using coolant with your CNC machine are:

• Lubricate the cutter
• Clear chips
• Reduce heat buildup

M07 [mist coolant] vs M08 [flood coolant]

The most common type of coolant used in CNC machining is flood coolant with the M08 code.

Flood coolant is where the cutter and workpiece are literally flooded with the coolant fluid. 

This works to lubricate the part, remove chips, and reduce heat buildup.

Mist coolant combines the coolant fluid with compressed air and sprays it on the cutting area. 

Mist coolant uses less coolant fluid and can be less messy depending on your CNC setup, but it isn’t as good at reducing heat buildup as flood coolant is.

Mist coolant is activated with the M07 code.

What are the other options for using coolant?

We discussed mist and flood coolant above but there are other options available as well including:

• Air: This type of coolant reduces heat and clears the chips, but it does not lubricate the workpiece. This type of coolant is used more often with sensitive materials.
• High pressure: High pressure coolant is similar to flood coolant. The only difference is that it hits the workpiece at greater than 1000psi. The higher pressure and higher quantity of coolant helps cool the cutter better and remove more chips.
• Through spindle: Through spindle coolant delivers the coolant directly where it is needed. It is better at clearing chips in many cases because the coolant from the spindle pushes the chips out of a hole or pocket.

Things to consider when using the M09 code

You never want to turn off coolant while the cutter is still cutting. 

On the opposite end of things, you should never turn coolant on if the cutter is already cutting.

Always start and stop coolant flow when the cutter is not actively engaged with the part.

Which other CNC codes turn coolant off?

The main M-code to turn coolant off is M09.

However, there are other codes that turn off coolant as part of their function including:

• M00 – Program stop
• M01 – Optional Stop
• M02 – Program end, no rewind
• M30 – Program end with rewind

Frequently asked questions about the M09 code

Does every CNC machine have coolant capabilities?

Yes and no.

You can expect that industrial level CNC machines will have coolant capabilities.

Home or hobbyist level machines such as CNC routers often do not have coolant capabilities, but they can usually be added on if needed.

This is sometimes called program end with rewind.

The rewind has to do with the way CNC program used to be read. 

They were on tapes or cards. Using M30 would tell the machine to rewind so that the machine was ready to run the program again.

The M30 code turns off the following machine functions:

• The movement of all axes
• Spindle rotation
• Coolant

The other code that can be used to end a program is M02. The M02 code ends the program but does not rewind the program back to the start.

The main function of both the M02 and M30 commands are basically the same, they stop the program.

However, there are a few differences to keep in mind.

Here is a list with the main differences between the two codes.

M02 is not used often anymore. M30 is the main code used to end a program.

M02 was used for a couple of reasons back when programs were on tape or cards.

Some machines were known to have issues rewinding the program and might destroy the program tape. In other instances, the program would be taped together as a loop which meant it didn’t need to be rewound. Continuing on from the end would loop back to the start of the program.

It is worth checking your machine manual to understand how your machine will read a M02 code. Some machines can even be set to read an M02 code as if it were an M30 code. Check your manual.

How to end a subprogram

M02 and M30 can be used to end your main program, but how do you end a subprogram?

The only way to end a local subprogram, subprogram, or macro is by using the M99 command.

The M99 code tells the machine to return to the program where the subprogram was called up. Usually this means returning to the main program. 

You can run subprograms within subprograms. This is called nesting.

Nesting can get tricky to read, so the majority of programs will only run subprograms from the main program to avoid confusion.

If the programmer ends the sub-program using M30 instead of M99, the machine will not return to the main program. 

M99 must be used to tell the CNC machine to return to the line after the subprogram command (M98) was used.

Best practices for using the M30 code

You should always take safety steps before stopping the program with the M30 code.

Always check where the spindle is before finishing the program. This means it is in a safe place where it will not crash or cause an accident.

For CNC mills this can mean rapid traveling the spindle to a safe Z-value before using the M30 code.

It is also a good practice to turn off the coolant using the M09 code before stopping the program.

The safest thing to do is make sure your safety blocks cover the required codes for each section of code.