Can't be that Hard?

This is my first post to the forum so excuse the random questions that I will ask. Live in Christchurch NZ, maybe there are some other users down here that may be able to give advice?
I ordered a MPCNC kit from Ryan thinking it can’t be that hard to learn how to use a CNC. I have assembled the mechanical parts and wired up enough to get the machine to be able to home the X & Y with the control panel. I didn’t order a Z axis probe, is there any other way of zeroing this axis without a probe is my question?
Will try and post a photo of the build so far in the next couple of days.
Thanks in advance.
Regards
Paul

There are many ways. If you bring the endmill towards the top of the material, you can eyeball when the tool hits the stock and use gcode G92 Z0. Or you can find something to use as a shim, and lower z until you feel the tip getting caught, and use G92 Z0.3 (or whatever thickness the shims got). If you want the stock to be perfectly flat, you can flatten it and use the precise same height as z zero.
BTW, welcome to forum! :grinning:

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A Z-axis probe at its simplest is just a flat conductive plate and a croc clip…easiest thing in the world to just make one.

There should be a menu item in the screen for set home offset. That should set all the axis to zero.

Unlike 3D printing, most MPCNC cutting is done relative to the stock, so your goal when setting up a job is to setup the home position relative to your stock as you’ve specified in your CAM program. Marlin (the firmware on your control board) is always zeroed in X,Y,Z when first started. If I’m not looking for high precision cutting (and I’m usually not), I manually place my machine in the position I want as home before starting the electronics. For the Z axis I place a thin piece of paper on the stock and manually lower the router by turning the lead screw until the bit just scrapes the paper as I move the paper around.

Some details:

  • If I’m not looking for high precision for X and Y, I’ll just push my router against the endstops for X and Y to square it, and then move the router by pulling on the middle of the tubing for each axis.
  • Marlin does not “lock in” your origin position until you move your router electronically…and each axis is independent. Thant means you can home your machine in X and Y electronically, move it electronically to a position and still manually set the Z height by twisting the lead screw.
  • If you’ve moved your machine electronically, then you can reset the current position to zero (or whatever) using the G92 g-code as Tubinbjorn suggests, or you can use the menu item on the V1 custom menu (assuming you have a display) as jeffeb3 indicates to zero the axes.
  • Touch plates (as Mike suggests) are an easy make and are also cheap(ish) to purchase most places. The only “trick” to using a touch plate, is that you must account for the thickness of the plate.
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A z-probe is basically a piece of metal with a cable and then another cable to the bit. Very easy to make on your own with a bit of spare change and 5 min of Google :slight_smile:

I use the same paper technique that @robertbu describes above but I normally use the manual jogging on the touchscreen instead of rotating the lead screw by hand.

Here is my typical process (note I use the Touch mode not Marlin mode).

  1. Home machine. I’m using endstops for squaring the X&Y axes.

  2. Jog the cutter over to the 0,0 position corresponding to the CAM origin and zero out X & Y on the touchscreen. Make sure the cutter clears your workpiece, clamps… before you move horizontally.

  3. Place a piece of paper between the workpiece and cutter and slowly jog the Z down with coarse moves (10mm) until the cutter is close to the workpiece. Switch to medium moves (1mm) until the cutter is within a couple millimeters.

  4. Finally switch to fine moves (0.1mm) and slowly move the cutter down while sliding the paper in and out with your other hand (short moves). Stop moving when the paper catches/snags on your cutter.

  5. Zero the Z axis on the touchscreen, jog the cutter up to remove the paper then jog back down to the XYZ origin/0,0,0 position.

  6. Start the program.

If I’m doing a really shallow or accurate cut I’ll compensate for the paper thickness by dropping the Z down 0.1mm to account for my paper thickness at the end of step 5 and start the program from there.

I have also used this method to pick up the sides of a workpiece (paper positioned vertically between the side of the workpiece and side of the cutter. The only extra step you need to do after the paper catches/snags on the side of the cutter is move the cutter over half a diameter + the paper thickness so that the cutter centerline is over the edge of the workpiece. But make sure you clear your workpiece in Z first before moving horizontally (i.e. move away from wall, remove paper, move up in Z then move cutter over edge).

You should probably use Robert’s hand method until you get more comfortable with your machine and then you can transition to jogging or getting a touch plate.

Hopefully this helps and let me know if you need any clarification.

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