Cut stops too early

After setting the parameters of the board I am to cut through, defining cut depth, Z height (I am not using a probe) and calibrating the zero point but the cutting process stops before reaching the defined value.

Have checked for mechanical reasons, and made sure that defined values are correct, still cannot figure out why I’m not getting what I see on the work surface. I’m defining tabs so the program realizes that I want to cut thru but doesn’t!

Any suggestions?

Hi Brian.

Do the carve technically finish?

If yes, try this - say you want to carve through 3mm sheeting:

  • Use your spoil board as reference, jog down onto it and raise Z = sheet thickness + 1mm (=4mm total)
  • Set carve depth in design to 4mm total
  • Carve

Any discrepancy in Z will now be your machine backlash/flex component.

Thx for reply Haldor. Yes carve does finish.
Will try your suggestion if I understand it correctly.

Get back to you.

Well I have read you reply Haldor and I think if you read the following it amounts to the same thing.

I lower the bit to my zero point so the it is just touching the upper surface of the board I wish to cut. This board is approx 3mm thick. This is my reference point. I then choose the cutting depth as 3mm + approx 1mm = total 4mm. Is this not the same as you suggest? This procedure does not result in a cut right through the board, so it certainly has something to do with a reference point.

If your step/mm value is off AND/OR mechanical aspect isnt perfect then measuring on top of the material to be cut wont result in a good carve.

When setting your Z-zero manually jog the bit down to the spoil board, then command a 4mm retract jog. (jogging incrementally untill the bit is raised 4mm void this excersise) If the bit dont raise above the material thats the first clue the step/mm value may be off.
If the spoil board is used as Z-reference, and commanded to raise 4mm and Z-zero is at this height, then a 4mm deep carve will end at exactly spoil board level. (Cut through)

But for simplicity sake do the following and report back to me:

  • Command a single 20mm jog motion on Z and measure the actual travel
  • Report what the GRBL parameter $102 is set to ($102=?)

Hi Haldor.

Jogging X.Y.Z Actual travel.

When set to 10mm X and Y move 10mm but Z moves only approx 4-5mm!

When I start GRBL and key $102 in the lower RHS field I do not get a value. Is it here that I should find a value? Nothing comes up in this field.

Hi again.
Looks like I must compensate by doubling the Z cut value. i.e 12mm to attain 6mm cut.

Can I send any screen shot values from the Machine Inspector for you to check the Z parameters?


To display the current GRBL values simply write $$ in Machine Inspector console window, followed by Enter. Under the console window your GRBL values will now be shown.

What does it say for $102?
What is the exact distance travelled for a 20mm jog command?

I´ll do the math for you once they data above is known :slight_smile:

1 Like

@BrianHoddy there was a recent thread about the same thing.

Hi @NeilFerreri1 and thanks for your response.

I assume that this value of $120 is found in Machine Inspector, at the moment it is = 10.000.

I don’t see anything abnormal here, but in practice when toggling value is = 10mm it moves 5mm.

There seems to be a discrepancy in the console text and the physical movement.

The X-carve default for $102 is 188.947. Do you have an X-carve?
What is your $102 setting?

Brian have a 3018-machine.

The GRBL parameter for Z is $102, if measured motion is half of whats commanded you need to change $102-value to twice of current. To change simply write $102=new value and press Enter.
Power controller OFF/ON and check using $$ that the new value is in place.

So if your current $102=100 the new value should be 200.

($120 is the acceleration value for the X-axis and not relevant for this issue :slight_smile: )

Aahhh… Then this thread might be relevant.

Hi again. Will double the value and review.


Hi again Haldor.

With the Z jogging movement set to 10mm pr command and jogging Z motor 5 times, the spindle has been raised 11mm.

Hope that clarifies things.


50mm (expected) / 11mm (actual) * 188.976 (current value) = 858.98

Enter $102 = 858.98

Then measure again.

I think the default for the 3018 machines is $102 = 800. You might want to start there.