Z height incorrect, rerun the job question

Hello Finally popped my nomad cherry. Did the wrench but it seems i didn’t set z zero correctly and i can see aluminum showing on the bottom. I guess I didn’t lower it far enough. Did the paper test. I haven’t removed the material yet, is it possible to rerun the z zero again and finish up the cutting?

what is the correct way of doing this?

thank you

Alex

It’s possible that your zero is fine but the aluminium plate is not exactly the thickness you think it is (did you measure it with a caliper?)
Anyway, if you still haven’t modified your zero and not removed the material, there are a couple of options to salvage this:
a) jog somewhere outside the material, go down to Z0 (Z=0.000), then jog to a slightly lower Z, by the value of the thickness you think remains at the bottom of the cut, or a bit more if you don’t mind cutting slightly into the wasteboard. Then (re)set Z0 (only!), and rerun the original job. Most of it will cut air, but near the end it should cut the remaining thickness at the bottom
b) OR modify your toolpath to increase max depth by the estimated thickness of the remaining material, and run the modified file.
c) OR modify your toolpath with a start depth of [a reasonable depth you know for sure has already been cut] and a total depth set so that it cuts the remaining material thickness, and run that modified file. This is just to spare time not cutting too much air, but otherwise has no benefit over option b)

Looks like you’re close (and that you had a successful cut before? Ghost image on the wasteboard)

If you haven’t altered the zero, I’d just reset the Z a bit lower and run again — or, rotate the stock and apply fresh tape and try again.

This was from previous owner.

Thank you Julien - I didn’t measure the thickness. This was sample material from carbide3d and wrench.nc file. I already shutdown the machine and remove the material I will try zeroing z again and flip the material over. Any good guides on how to set the z height correctly? should i get the probe?

Oh, I did not realize the wrench example came as a g-code file (.nc) and not as a Carbide Create design file, so my suggestions above to adjust cut depth would not have been possible anyway. I wonder if the design file for the Nomad wrench tutorial is available somewhere (@WillAdams do you know?), it would be easier to finetune the depth of cut.

As far as I see in the wrench.nc file, the toolpath is set to cut down to 0.12" / 3.048mm deep.
Maybe you can measure the actual thickness of your material, this will give you an idea whether it’s “normal” that the cut did not go all the way through. If you get the same problem a second time, as @WillAdams said you can just reset your Z zero slightly lower and rerun the job.

As far as a good way to set Z zero, probes are nice but what they do is mainly make the zeroing process faster, not necessarily more accurate than manual zeroing using the “paper” method. I would suggest that you do a few projects using the manual/paper zeroing, then once you are familiar with the process you can decide if you feel like you need the probe.

The (very common) way I do the paper touch off is:

  • jog down towards the surface using 1mm increments until you are about 1mm away
  • reduce jog step to 0.1mm
  • slide the paper back and forth continuously and jog 0.1mm at a time towards the surface, and as soon as you cannot slide the paper anymore, that’s where you set your Z-zero. Since the average paper is 0.1mm thick, this gets you very, very close to a perfect Z zero.

(disclaimer: I don’t have a Nomad but a Shapeoko)

Ah thats what I was missing. I didn’t let paper grab enough. I felt it dragging but i was still able to move the paper. I do 3d printing so I’m familiar with paper method. Will lower z and try again.
thank you

I worked up METAPOST code for a wrench at:

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As you discovered, that is the difference between the paper method for CNC vs. the paper method for 3D printing. For 3D printing, you want there to be a gap of the paper thickness (~0.004" or 0.1mm) between the nozzle and bed, but for CNC you want there to be no gap, and the cutter digging into the paper a little bit gets it very close to Z zero.

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