1

So I have been having this issue for a while now, when I start a print, even though the bed is perfectly leveled with A4 paper, the z axis will stay about 2 mm above the build plate and start printing. When I click Z axis home in the settings, it goes perfectly back to where I leveled it, but when it starts a print, it is far from the bed.

From what I have read on forums some people suggested that changing the bounce back distance of the z axis when it double homes might help the issue, but I am having a problem finding where to edit that in the firmware. I am using Skynet 2.3.2, and even had this issue when I was using the stock Anet A8 firmware. I am also using Slic3r, which I have been using with this printer for the past year with no issues.

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Do you have a stocked z-stop sensor or a proximity sensor? Do you have auto-leveling feature turn on in Skynet3D? It happens to me few times because a faulty proximity sensor. Most the proximity sensors sold in the market are rated 6-30v. Some of them works in 5v provided with controller board. In some case, it is not reliable if 5v is used.

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Sorry I am using the stock Anet A8 endstop switch. I was able to find the code to raise the bounce back of the Z axis from 2 to 5, but that has not fixed the problem.

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It did not happen to me before I change the z-stop to a proximity sensor. Have you tried M119 gcode to verify the switch? I will move the nozzle 1mm and 2mm above the bed, and using M119 to see the z-stop is triggered. Maybe swapping the endstop switches will help. I am also wondering the “real” endstop will help(it provides 5v to the signal when is not trigger vs the open circuit. Like this one, https://www.aliexpress.com/item/For-Endstop-Mechanical-Limit-Switches-3D-Printer-Switch-with-cable-for-RAMPS-1-4-CNC-3D/32766668840.html?spm=2114.search0104.3.67.r3IG8D&ws\_ab\_test=searchweb0\_0,searchweb201602\_3\_10152\_10065\_10151\_10130\_5490020\_10068\_5430020\_5410020\_10307\_10137\_10060\_10155\_10154\_10333\_10334\_10056\_5370011\_10335\_10055\_10336\_10054\_10059\_10332\_100031\_10099\_5400020\_10103\_10102\_10052\_10053\_10107\_10050\_10142\_10051\_10324\_10325\_5380020\_10326\_5390020\_10084\_10083\_10080\_10082\_10081\_10178\_10110\_10111\_10112\_10113\_10114\_10312\_10313\_10314\_10316\_10078\_10079\_10073\_5420011-10050\_10332\_10333,searchweb201603\_2,ppcSwitch\_2&btsid=01797540-8556-4fe2-9c2f-3810d6aaa4a4&algo\_expid=2fd72cf2-0a2e-4cb0-b4e9-90a1d1dcd5da-8&algo\_pvid=2fd72cf2-0a2e-4cb0-b4e9-90a1d1dcd5da&transAbTest=ae803\_1

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So I have tried a few more things since I originally posted here. I have used multiple slicing programs to see if it was a slicing issue, and even looked at the Gcode to see if it was unnecessarily raising the z axis; though I did not find anything out of the ordinary. I have also switched the x axis endstop with the z axis endstop to see if maybe it was a bad switch, but still the problem persisted.

The bed raises itself 9/10 times I try to print. I don’t know if this is just coincidence but it seems when I don’t heat the bed, the issue doesn’t occur. But I will have to do more testing to see if this is true or not.

If anyone else has any more suggestion that would be greatly appreciated!!

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Does Z value on the LCD shows 0 when it happens? Unfortunately, it is difficult to troubleshoot without investing more money. The endstop switch I mentioned before does have a LED on it, and it will be interesting to know the LED is on or off when it happens compare to when it is not. Or investing a auto-leveling sensor to see it will help. I checked the SkyNet3D firmware and there is nothing point to the problem. The newer Marlin firmware starting from v1.1.4 supports Anet board and Anet keypad. You can’t copy the configure.h file from SkyNet3D to Marlin, but you can set the same value if you see fit. I can help you, but I don’t have one since I change my board to MKS GEN 1.4 when my motor driver burnt.

I have so many spare parts that I can actually build another printer if I have the frame. I can easily troubleshoot the problem with the spare part. In your case, I might want to try a different controller board, even it is a small possibility.

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The LCD does display 0 for the z-axis when it beings printing. So I found out something interesting, it seems when I have the heated bed set to 100 C the leveling issue occurs, but when I have the bed set at 60 C it levels fine. Because I am printing with ABS I need to print with a very hot heated bed, but I don’t know why this would cause a leveling issue.

I just replaced the heat pad with a 200W silicone heater, because this is drawing more current, could is possibly by screwing up with the accuracy of the endstop? I am debating on buying an auto level sensor, but I would hate to waste money on one if I don’t need it.

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So I have finally figured out the issue!

The heated bed is getting so hot it is actually wrapping the bed itself. I decided to level the bed with paper and leave it right at the origin, then I turned the heated bed to 100 C to see if it would stay in the same place. The bed lowered about 1-2 mm after it was heated to those temps.The construction of my Anet A8 is in this order. 0.8 mm PEI build sheet which I placed over the aluminum build plate. There are screws and spring in the four corners that attach to a 1/4’ acrylic bottom piece; which is then connected to the bearings.

I’m assuming that with the temperatures the heat is transferring down to the acrylic and slightly wrapping it. I don’t think the aluminium build plate would warp at only 100 C, and i’m pretty sure the springs should keep there stiffness under those temperature, but please correct me if i’m wrong.

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Congrats! 1. I only heat the bed to 90 when I print ABS. 2. Auto leveling sensor might help you, because it triggers based on the same distance from the bed. The end top switch is mounted on the frame.

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