# Steps/mm Calibration

Just a quick comment to the video’s author. The calibrations were correct on the X and Y, but the way you calibrated your Z was wrong. This is because after calling G92 (which isn’t actually needed. More on why not in a minute) you moved down to your work surface which was a pre-calibration move, which would then have thrown off all future measurements from zero because you don’t actually know you’re at true zero yet and definitely won’t be if your ratios are off.

I’ll over-exaggerate the numbers to better visualize the problem with how you did it. Say your touch-plate was 5mm thick but your \$102 was off by a factor of 2 (was 80 when it should have been 40.) You touch off the top of the plate, then set G92 Z5 (because you know you should be exactly at Z5), then say ‘Go to zero’ but your tip plows into the surface of your machine thinking it had only moved 2.5mm so far. That’s because the ratio was off while you were moving to zero.

Say the reverse was true and your ratio was off by a factor of 0.5 (you have it at 20 and it should be at 40) and you said 'Go to zero. This time you’d stop at a point hovering 2.5mm above your work surface although the machine would be reporting you’re at zero even though clearly you’re not.

Both of those would be obvious that something was ‘off’ and you couldn’t just ‘measure from zero’ but say you’re only off by 0.1mm. You may not notice that and are measuring from a zero that’s actually 0.1 off as part of your calculations.

But as I said above, you don’t need to set zero to calculate your ratios anyway. You only need to be able to move a relative, but exact distance from a known point, and you have that known point–the top of your touch plate–thanks to your probe!

As such the proper way to calibrate Z is to probe down to the surface of your plate then simply issue a relative Z move (set G91 for relative coords, then issue M0 Z20 or whatever the actual thickness of the extrusion is, which you can easily measure with your tool) and measure where you are relative to the top of the extrusion as the extrusion sits on top of that plate, not the surface of your machine! Again, at this point, the surface of the plate is the only absolute, which is why neither the plate’s thickness, nor where zero actually is actually matters yet.

When you measure everything from the top of the touch plate, this guarantees all Z-axis movement is considered in the adjustment calculation, which is what your initial jog down to Z-zero missed and threw off.

Once you’ve set all your ratios, then go and re-probe, and set your G92 to identify zero because at that point, all ratios have been properly adjusted so you will be at true zero then.

Hope this helps!

(Note: I’ve copied and pasted this into the video page’s comments on YouTube so he’ll see it there as I’m not sure he even knows his video is linked here.)

Where and how do I access these commands to adjust my z?
My stock layers appear to be way too deep.
FYI I just got my unit up and running about a week ago and I am working to calibrate it

Hello…I am rizalyn. We have 30 inch cnc longmill at home and I’m having trouble with my machine because the machine locked up. And I dont know how to fix it. I have no idea what to. I hope someone can help me. Thank you.

Locked up in what way?

Perhaps the controller throws an error or is awaiting a homing unlock sequence, or status reset.
Try to send a \$X or \$H command through the controller.

It locked up when I install a gcode sender because I want to carve an image but it didn’t work. So when I go back to sign in my easel the machine didn’t work any more.it was only having a sounds but not moving any more… so we can I find that controller? Thank you for your reply.

I would suggest making your own thread for clarity, where you in detail describe your hardware and workflow + where it is snagging.