Cnc4newbie z-slider added and works, BUT!

I installed acnc4newbie z-slider added and it works, BUT! I just found out my z is 3.5mm off. I just started trying 3d carves and every time I start a new project on the initial plunge of router is going deep. See #1 below. I have zeroed x, y, z with paper. #2, in the fast jog page I can click the fast to x,y and bit goes there perfectly. When I click the z plus 6mm bit goes there. Now the problem, #3 below. I measure with tape measure from top of project (z=0) and measure to bottom of bit (z+6mm) and it measures 3/8" which is 9.525mm not 6mm. I am off 3.5mm!! Everything I try is doing this. I have all grbl settings updated as per Chris Powells video.

  1. 1st cut depth 3/16 = 4.7625

  2. Current x, y, z+6mm settings carbide motion
    x = 0
    y = 0
    z = .236

  3. Actual measurement surface to bottom of bit at z+6mm
    Frac = 3/8"
    mm = 9.525
    Dec = .375

So what are your configuration values and what is your z stepper steps set up for? Did the company supply parameters to set up. Additionally what are you sending gcode with? CM is much more than a gcode sender and controls a lot of function on a Shapeoko/Nomad which may not be compatible with 3rd party parts.

You say it’s always 3.5 mm off, but is that always over a 6 mm intended delta? You only specified the error between one pair of points. Could it be that if you move to z+12 that it’s now 7 mm off? This would point to the steps per revolution setting being off — one of the many settings @gdon_2003 is referring to.

Also look at the behavior during homing. When a Shapeoko homes, it touches the switch, then backs off from the switch a know distance — 3.0 mm, if I recall correctly. If you’re no longer backing off by this amount (and CM is unaware), or if you’re backing off further after contacting the homing switch, it could lead to a constant Z offset. This is less likely, though… if you have this issue, you probably also have the former issue.

When the machine starts doing something you can’t explain, throw out all your assumptions, grab your ruler, square, calipers, and dial indicator, and start systematically checking all the basics to narrow in on which step of machine operation this error is being introduced. Questioning assumptions is critical to troubleshooting; if all your assumptions were correct, you’d have already found the issue.

One more thing… it might be easier to pick one decimal unit system and stick with it through the troubleshooting process. I’d suggest whichever unit system you’ve configured your controller to use, since it’s one less conversion to keep track of.

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@gdon_2003 FYI the back-off behaviour in the GRBL controller is there to stop the axis constantly tripping the homing sensors. The sensor trip coordinates define zero, and then GRBL moves the axes to -3.0mm,-3.0mm X,Y to stop the sensor interrupts from constantly firing on the processor. You can edit the 3mm to a different value, say to marginally speed up the homing cycle, but it makes no difference to the zero point the machine has detected with the sensors

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OK, lets see if this makes sense to you all! My first post was not clear to you.

I installed acnc4newbie z-slider for shapeoko and it works, BUT! I just found out my z is 3.5mm off.

  1. New project setup. I set x,y and z to 0,0,0 in carbide motion.
  2. I then go to the Rapid xy Position. I click any of the icons on screen to move to any position on router, works great. Next I click “Current Offset x,y” and my machine goes exactly to my set x,y coordinates.
  3. I then click “Current Offset (Z + 6mm)” my router moves z to what it says is z+6mm. I then use my tape measure and measure from top of project (Z0) to the bottom of the endmill.
    Actual measurement surface to bottom of endmill at z+6mm
    Frac = 3/8"
    mm = 9.525
    Dec = .375
  4. My machine is now at x=0, y=0 and z=+6mm. I then go to the “Set Current Position” and look at numbers. Carbide Motion shows z=0, y=0 and z=.236
    .236 = 6mm
    .375 = 9.525mm
    Difference = 3.525mm or .1388

If I try to cut a file the 1st cut of endmill goes down into wood by the .1388 and then starts cutting. If I let it go it works BUT it will also go through my wood (.75”) and into my spoil board by .1388”1st cut depth 3/16 = 4.7625

can you jog the Z axis in the air by a given distance (as displayed in CM), say 10mm, and measure how much the Z axis actually travels?

9.525mm (real) versus 6mm (commanded) is x1.5875, which happens to be very close to the x1.6 ratio between the number of steps for a Z+ (200) and for a HDZ (320), but I suppose you used a different value for $102 anyway ? I’m not familiar with that Z axis setup procedure.

Might be worth double checking your $102 value from the MDI / log window

EDIT: found out the CNC4Newbie slider uses 200steps/mm. If you inadvertently configured it a HDZ from CM settings, it would tell GRBL to do 320steps for each commanded mm to move

I had asked in the first reply what the Z stepper motor was set up for. No answer. This is like Julien said most likely a Z stepper motor steps per MM setup problem. You have to calibrate for that. The C3D stuff are known and you set them in t he configuration. For your 3rd party you have to either calibrate it manually or use the parameters the manufacturer supplies.

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$102 set to 200 which is what is called for for my setup. I am using aspire 9.5 for creating gcode.

So as Julien suggested. Zero your bit on the waste board. Move your Z to 10mm and measure. You have to calculate the actual height compared to the 10mm cm thinks the height is. Change your Z steps per mm and try again. Tweek until the z is calibrated. Even the c3d equipment needs tweeking on some machines.

Since you are always high you need to decrease your steps per mm for z. If you were less than 10 mm you would need to increase steps per mm.

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Finally got back to my shop. I dumped the GRBL settings and yes, my $102 some how was set to 320 instead of 200. Reset back to 200 and ALL is good. I have done 1 basic 3d file and it came out good. Doing a more intricate one now. Thanks everyone who helped. I am understanding grbl more and more.

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Glad you are fixed. I think the Z 320 setting is for HDZ. Not in font of a machine to verify but that sounds right. Since you are running a 3rd party Z what do you use in your CM setup as far a Z type.

This is what nc4newbies call for with their z-slider.

$3=2 - Port Direction is different for new Z axis
$20=1 - turn on soft limits
$102=200 - Z axis step/mm
$112=2000 - reduced max speed of Z axis for better movement
$122=750 - Z accel mm/sec
$132=150 - Z max travel in mm

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