# Beginner Question

How do you or the machine know to stop a project to switch to a different style bit?
Thanks!!

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Hi Jeff. Welcome to the forum. The question is a good one and the written GCode has within it the ability to stop the machine and let you change the tool. In the GCode you will see the commands T and M6. T command will get the tool number (from the tool library) and will know that tool is used at the start of the carve. The M6 command is to stop the machine (from moving only - unless the spindle speed is also controlled by your system)

Like all things there is an important caveat. Tools may not be same length and if you have two different length tools, at the tool change, you will need to know how to adjust the length so that both tools in a two tool change situation, are machining from the identical Z height (zero point).
A practical example is thisâ€¦ when I carve in 3D (tool moving in X,Y and Z directions simultaneously) I use a roughing tool to take out as much waste material as I can and I do it as quickly as the stock permits. I then use a finishing tool to carve the fine detail. Carving in X & Y directions simultaneously is 2.5D and while in can to some extent mimic 3D in the final resultâ€¦ it is not 3D carving.

I am in the middle of a project right now. I am capturing the process on video so you will see how tool change operates with simpler machines than the one in the example video. If you do not have a tool length measurement device, you must measure all tools from the zero z height and if you have machined the stock away with the first tool, this will not be possible. I would build up a Z height gauge (to the same height as your Z measurement) so that you can measure multiple tools from the tip resting on the gauge, if you have no tool length measurement device.

Do not be concerned about the complexity of this system shown in the linked video below. The guy goes into the two commands (T and M6) for tool change and all GCode uses them.

Hello @Rstd2005, and welcome to the forum. Everything that @jepho said is correct but it is also possible to just create separate tool paths for each bit. You then basically have multiple jobs that are run on the same piece of stock. You simply run the tool path and at the end the machine stops because itâ€™s the end of the â€śjobâ€ť, then you change tools, re-zero the Z axis, and run the next tool path.

This is not meant to discourage you from learning about the T and M6 commands, just an alternate, and in my opinion, simpler method. I have done many jobs using multiple bits and still need to learn how to do it with the T and M6 commands. I guess itâ€™s a case of â€śif it ainâ€™t broke donâ€™t fix itâ€ť or just me being lazy!

Anyhow, welcome again to the group Jeff.

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Wow Thanks!! I will check out the video!!

Cool I donâ€™t have the machine yet It should be here by Wed-or Thursday.
Just been immersing myself with as much as I can before i try it out!
Thanks

I agree with Michael, and thatâ€™s the way Iâ€™ve been doing things.