Hi everyone, I’m struggling with a Z-axis depth issue on my X-Carve and could use some fresh eyes. My Z-axis starts at the correct depth, but gradually “climbs” out of the material as the carve progresses. By the end, it’s just cutting air.
Machine Specs:
The Evidence (Photos Attached):
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Photo 1 (Success): The circular “Mr. Carpenter” logo came out almost perfectly. This job had longer, continuous paths.
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Photo 2 & 3 (Failure): The “Wood Shop Teacher” award plaques. You can see the bottom text is visible, but as it moved to the top/right, the bit lifted until it stopped touching the wood entirely.
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Photo 4: Another example of the “N” panels getting shallower from left to right.
What I’ve tried/observed:
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No Noise: I am NOT hearing any clicking, grinding, or stalling from the Z-motor. It sounds smooth.
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Plunge Rate: I slowed the plunge rate down significantly, but it only provided limited results; the lift still happens.
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Mechanical: The bit is tight in the collet and not slipping up.
Since the circular logo worked but the text-heavy awards failed, I suspect the issue is related to the frequent lifting/retracting moves. Does this sound like a Vref/Potentiometer issue, a Motor Coupler slipping silently, or something in the GRBL settings ($1=255)?
Any help is appreciated!
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I would check the motor coupler first and make sure both set screws are tight. You are probably losing steps. You can try reducing your depth of cut. Maybe I’d make a mark on the shank of the bit and see if it’s moving in a worn collet too.
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Good morning, thanks for the comment. I checked both of those are tight and I sent my collet through my ultrasonic cleaner to make sure it was not dirty/loose. I would understand a loose collet if it was cutting deeper than I wanted ( as if the bit were falling out and going deeper) this is I am loosing depth from left to right. I don’t speak CNC fluently yet…. still learning and trying. I feel like it is a software setting as it it uniform across the cut.
Cheers
Keith
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OK…next thought…did you level the bed and check for squareness on the machine. Sometimes the bolts need to be snugged up. Just a thought. Any loose wires to the steppers? Is the wood warped or an in consistent thickness? These are just some things that can happen.
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The bed is only out 3mm at any given point across the Z axis. I haven’t leveled the bed (I feel like i’m going to but, I fear it will only do the same thing of the rise. I will look at all the connections today after school.
Thanks for the help/sounding board.
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Not sure but can you rotate the Z axis stepper motor by hand when the program is at idle? Does anything change when to set $1 to any other value other than 255?
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Just found the description.
$1 - Step idle delay, milliseconds
Every time your steppers complete a motion and come to a stop, Grbl will delay disabling the steppers by this value. OR, you can always keep your axes enabled (powered so as to hold position) by setting this value to the maximum 255 milliseconds. Again, just to repeat, you can keep all axes always enabled by setting $1=255.
The stepper idle lock time is the time length Grbl will keep the steppers locked before disabling. Depending on the system, you can set this to zero and disable it. On others, you may need 25-50 milliseconds to make sure your axes come to a complete stop before disabling. This is to help account for machine motors that do not like to be left on for long periods of time without doing something. Also, keep in mind that some stepper drivers don’t remember which micro step they stopped on, so when you re-enable, you may witness some ‘lost’ steps due to this. In this case, just keep your steppers enabled via $1=255.
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Good looking out. The $1=255 is set to 255. here are my settings from the machine. Also I can move the Z screw drive when it is idle.
$132=100.000
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$131=750.000
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$130=750.000
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$122=50.000
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$121=500.000
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$120=500.000
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$112=1000
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$111=8000.000
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$110=8000.000
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$102=49.909
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$101=26.660
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$100=26.660
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$32=0
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$31=0
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$30=1
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$27=1.000
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$26=250
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$25=750.000
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$24=25.000
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$23=3
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$22=1
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$21=0
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$20=0
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$13=0
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$12=0.002
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$11=0.020
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$10=115
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$6=0
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$5=0
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$4=0
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$3=7
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$2=0
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$1=255
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$0=10
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Try setting $1 to 64 or 128
If the spindle drops faster you might have a flaky stepper motor. I have had several stepper drivers that have vr’s on them for current setting that might need adjusting. You also want to slow down the step rates.
Another check easy relatively easy check is to swap the motors around and see if it still happens.
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good morning,
I was unable to swap the motors around because the pressed on belt drive gear on the Left and right motors. I did pull it all apart and reconnected everything and still no relief. I am going to try again over this summer to fix my CNC before school next year. I think I am going to get a new stepper motor and swap them.
Thank you for all your help.
Cheers
Keith
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Are you very sure that the pulleys are pressed tight and not slipping. Try putting some witness lines to raise the confidence level that no slipping is happening. I would try making a scale staircase to get an easy visual on it’s movements. I suggest a 1 mm rise for each step for the range of Z axis and run it a couple of times. The reason that I think that the problem is mechanical is because it is very rare for this type 0f G code to self compile and that the kind of computers that we use aren’t smart enough to write their own intermittent program code.
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Pulleys are tight and I am now running a step test on a .5 “ plywood board. I know Plywood is not perfectly flat but, its a good stand in. I’ll let you know when it’s done.
Cheers
Keith
P.S. Ron, thank you for your help.
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I would suggest running the staircase from acrylic as it may show you more. 1/4" thickness and 1 to 2" width cut over several inches. More is better and please remember that I am only guessing. I had a similar trouble with a 3018 that I worked on in the past. No definitive solutions but I suspect that replacing the Y rails and squaring the rails and replacing the motors solved it for me.
This is one of my fixtures that I would test it in at least 3 places on the frame rails I modify it frequently as a guide
good fortune
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My buddy just told me that I wasn’t clear.
Start with a piece of the hardest material on hand. This material is set so that the material is parallel to the Z axis (at least close enough). I am not trying for exactness as I would mainly be looking for differences in the cut across the table as an indicatory of change of speeds caused by the spindle movements.
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