Changing Bits in Middle of Cut - Pre-pocketing

Has anyone here tried setting up a cut that uses a pre-pocketing bit? I just did, but I can’t figure out how to go about changing the bit. When it came time to change the bit, the program just paused, with the bit right down at the cutting level. I eventually got it raised and got a new bit in, but then I couldn’t figure out how to get it back to where it was when it paused. Anyone know the technique for doing this?

I want to cut the t-slot pockets for my spoilboard, but using the 1/8 bit took 45 minutes for one (I need 10). The 1/2 inch router bit did the bulk of it in 9 minutes, but it won’t do any good unless I can get the 1/8 bit back in and lined up correctly.



Are you using an LCD controller or Repetier Host? In “theory” you should be able to use the Move commands in either GUI to lift Z so that you can make the change and it should still maintain it’s origin reference. Of course you have to be very careful not to move the steppers or they will be off by that much. I say in “theory” because I have not tried this :slight_smile: Let us know if this does not work.


Yes, I need to experiment with it more. I thought I’d be able to raise the z with the LCD while it was paused, but maybe didn’t click/turn just right. It would have been easier if I had a computer hooked up running repetier host. I was using a test piece of wood, but was anxious to get on the the actual job of prepping my spoilboard, so I just redid the gcode without the tool change.

I’ll give it another try sometime and report back. Thanks!

To move an axis with LCDs select prepare and scroll all the way to the bottom.

Thanks, Steve. Yes, I’m able to move the various axes with the LCD. That’s what I expected to do when it came time for the tool change, but I only had the LCD and probably clicked something wrong on my way to the Move Axis menu, because the program resumed with the DW660 switched off. By the time I killed the program, moved everything around and got the new bit in, there was no way to get back to where I was - at least, not without pulling the SD card, editing the gcode to delete what had already been done, rezero the machine, etc. I would have much better control with gcodes sent through repetier host, so I think I will get a computer set up for that - I have an old laptop standing by, just haven’t gotten around to making a space for it.

Has anyone tried using repetier server with the MPCNC?


I am also wondering how to restart repetier after it stops for the tool change.

Split your job to several smaller jobs. For each tool one job. When finished it will move to 0 X and Y. Move the Z in repetier host, change tool and lower it back. Of course the 0 on Z won’t be perfect, maybe 0.1mm off if you have different tool length. It is raher hard to get it spot on. A Z-probe would be helpful. Then start the second job. Just take care not to move motors and turn off motor disabling in g-code and repetier host. This works reasonably well using repetier host and fusion 360 postprocessor from the forum. BTW there is a nice repetier host plugin with CNC GUI.

What I’ve done a couple times to rezero the z is put the new bit in and leave it long, but not tighten it all the way. Run the z back to zero over a noncut part of your workpiece. Then tighten it down the rest of the way. Gets it pretty close.

I just manually enter G92 Z0 when I’ve got the new bit down to the work surface, that resets the zero point…

Yea, that works too! It’s my second script in repetier.