Pre-cut setup process

Hi - I’ve recently got my MPCNC up & running (build here) with a few test cuts under my belt.

I’ve done quite a bit of reading & haven’t seen any mention of processes/methods used to set the machine up before starting a cut.

I’m currently ‘printing’ from the SD card on RAMPS - from what I can tell, the mpcnc zero’s all axis when powered up, & doesn’t take any further commands to re-zero after being powered up (applying home offsets doesn’t seem to do anything).
I’m specifically interested in methods where you can align X & Y to square, turn the machine on & power the steppers, then move the spindle to the point where you want to cut, re-zero, then start the cut.

Can anyone provide the methods they use to get setup, even if it doesn’t cover all of the above points.


G92 X0 Y0 Z0

to the top of your gcode file, g92 tells it to zero.

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This is mostly how I start all my projects. I also have G92 x0 y0 z0 as a button on the manual move tab in repetier.

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From my understanding, the machine assumes everything is at 0 when you tell it to start a job.

I can either power up the RAMPS, move the spindle (by hand, not with jog dial) to where I want it and then start the job, or I can move the spindle (by hand), power up the RAMPS, and then start the job.

I just grab the xy carriage and push it to where I want zero to be and then use the pineapple to lower the z until it’s just touching the top of the board I’m cutting.

Either way, the machine still thinks it is at zero because it doesn’t have any feedback for if you manually move the spindle.

Now, if the software had encoders on the steppers so that as you moved the spindle by hand it could read that you’re moving it, then its 0’s would change.

If you’re using the jog dial to move the gantry to where you want it to start, then you’ll need the G92 code provided above to zero out the axis before it starts.

That is incorrect, unless you have something like a G92 in your gcode, or you haven’t powered on your motors yet. But you’ll get pretty frustrated if you try to run another gcode after the first and you aren’t paying attention to the coordinates.

My machine was a different vintage, and I’ve disassembled it for the Low Rider parts. But when I did it, I had a problem with squareness, so I would always start at one end, holding against those spacers, then power on the CNC, move to energize the motors, and have the software/screen move it to the work place start, then rezero everything (with a G92 X0 Y0 Z0). Then I would move up a few mm with the LCD, turn on the vac, turn on the router, and print from SD.

I also sometimes go to the extremes of the cut first, just to make sure nothing will bind, and I sometimes use the machine to mark holes for clamp screws. For example, if I’m cutting a hole (not pocketing it, just cutting the outline) in a big part, I like to put a screw in that to help hold the middle of the work down. So I’ll take a note of the coordinates where I can put a screw, and after I’ve set the origin (G92), I will move to that spot, turn on the router, and dive down about 2mm into the workpiece, go back up, turn off the router, and go back to 0,0. Then I predrill and fire in a screw there.

Chaps - this is all awesome input, thanks.

Jeffeb3 - I think your approach is closest to what I have in my head. I’ll read through all these again tomorrow, take stock & decide the best way forward for me at the moment.

I’ve already added a G92 to the script start section in Estlcam, so that’ll be in place at the weekend when I next get to have a play. This alone will help a lot & prevent having to reboot RAMPS every time when i’m doing a set of small cuts.

Just make sure you remember that. Especially if you do something like separate different tool paths into different files.