Can anyone explain what happens at tool change?

Not sure this question belongs here, but I wasn’t sure where else to put it. After getting over several early issues (thanks to the help of people here!), I finally have the x-carve up and running. I’ve quickly realized, however, that I need to start using a larger roughing tool and a smaller finishing tool or it’s going to take an entire day to carve just one model. So last night I processed my first model in Meshcam using a big roughing bit and then a 1/8 finishing bit. I will send it to x-carve using UGS. I don’t see anywhere though that says what happens when it comes time to change out that roughing bit. Does UGS pause the x-carve and send it back to the home position (at some elevated Z position to aid in bit removal I assume)? Then there must be some sort of “resume” button to get it going again? If this is how it works, how does one make sure your Z height is back to the proper home position after inserting the new bit?

Anyway, I thought it would be nice to know what to expect as I try this new carving process.

I find it best to save the toolpaths as 2 different files. I run the roughing pass. When that completes, I change bits, re-zero the z-axis then load and run the finishing pass.

Ah, interesting! I never thought one could do it like that. I’ll have to play around and see if Meshcam is even set up for that. In the “standard” workflow, it simply saves the roughing and finishing processes in to the same g-code.

There should be a way to split it up, I don’t use meshcam, but I am sure it is there.

I usually run 2 separate files as well.
When the first finishes, the spindle should return to x-y zero and have z at a safety height above that point.
Leave power on to the steppers, this locks your motors and holds your position against most accidental bumps that would result in a loss of position.

Change out your bit, and re zero the z, I use a touch plate. confirm that you are at x-0 y-0 z-0 and run the second, finishing file.

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two files here too… the thought of the machine having some amount of control still makes me uneasy. I’ve seen Irobot and terminator.

Okay, you all have me convinced. Two separate processes it will be! :slight_smile: Still slightly nervous about changing out that tool. I would imagine that if you aren’t very precise in making sure you home the finish tool exactly the same as you homed your roughing tool, everything will be off. I guess I’ll find out shortly.

After the first job completes the Spindle with return to the work zero position.

Remove the old bit and load the new bit without moving the X and Y position. The motors should still be locked so just be careful when torquing the collet nut that you do not over power the motors and move the carriage. You can use the jog controls to move the Z axis up if you need additional space to remove the old bit. (Just don’t move the X or Y)

Then re-zero the Z axis for the new bit (Very important to remember to do this step!) then just start the second job. The work home is still exactly the same as the the first job and all will be fine!

i mounted a cheap laserpointer somewhere random to my carriage. I mark the laser point before roughing, then after that pass I change tools, check if the laser still hits the same spot, zero the Z and start the finishing pass.
but if you’re careful enough, the motors should hold their position. Note that not all software export gcode with a ‘return home’-command at the end. but you can always give the command manually


I also put a cheap laser pointer (actual projects two perpendicular lines) to side of my spindle mount and that has been very very helpful. It makes it easy to set the work home position and like you say it is very easy to spot if anything moved between bit changes,

I highly recommend the laser pointer upgrade! I have a thread here somewhere on the one I purchased.

Very good idea on the laser pointer. I’ll look in to that!

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I have a question about the reseting of the z-axis
For the tool change i have a m00 in my g code file, which stops the programm
But when i want to move the machines in the machine control register of ugs, the buttons are disabled so i can’t reset the z-axis
Am i missing a line in the g-code file or something?


M00 is not how you should be ending the program. Use an M30 instead.

I thought m00 is for ‘hold’ and m30 is for programm stop?

But i want to hold the programm for a tool change an continue after reseting the z-axis with the same file. I want to use the one file for rough pass and detail pass, but the command buttons in ugs are disabled when ‘hold’ is activ

I was never able to get that to work with UGS. I found it much easier to just create multiple toolpaths, one for each bit.

Load a file, zero all 3 axes, run the file, change bits, rezero the Z-Axis, then load and run the next file.

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What was your problem when using one file?

Same thing…no way to rezero the Z-Axis after a tool change.

Okay, thank you :slight_smile:

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I would be a bit “superstitious” just letting the machine be on hold for a tool change…

With UGS you can use a zero plate or triquetra zero block at and use his excel guide for zeroing xyz or just the Z it’s a free download.