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z-axis limit switches

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r6502:
Hello all,

I'm new in this theme - I bought a used Anycubric Mega S.

I tried to adjust everything, but got different result when printing the same part, especial for the 1st layer.

I started to investigate and found out, that the used switches for both z-axis generate a real large tolerance of the final hight compared to  the hot bed.

In my case it was in the range of +-0.12mm, but sometimes it was also +- 0.2 mm. I measured this on both z-axis.

Is this related to the used switches? Has somebody tried to replace the switches with photo sensors, that are more precise regarding the switch position and the repeatability? This should result in more precise levelling position of the z-axis.  The x- and y-axis does not be that imported, as these axis are only related to the position, where on the base the part is printed.

It would be interesting to her your comments..

Have a nice weekend - Guido.

thm_w:
Mechanical switches are more than accurate enough for your average 3D printer. From what I see in photos its a normal metal arm microswitch, which is typically used.

Either:
- Switch is damaged or dirty
- There is mechanical slop somewhere in the system (something loose, broken, etc)

Check that the switch is soldered in place, joints are not cracked, and try moving it around and activating it with your finger.
Spare endstop switches are cheap (<$2), so might be a good idea to have some on hand.

https://3dprinting.stackexchange.com/questions/1109/which-endstops-are-most-precise

CatalinaWOW:
What did you uses to measure this variability.  I have encountered many problems with the spacing of the hot bed relative to the nozzle that are unrelated to the limit switch.  Check for anything loose in the vertical drive chain.  Check that level adjustment screws are not rubbing against cabling or items near the printer.  I have found that prints that are difficult to remove from the bed often result in changes in bed height.

Don't get discouraged by all this.  Once you have your process all tuned in they do tend to stay solved for long periods.

r6502:
Hello all,

thank's for your input.

I had a clocer look today at the device, and found out, the the z-axis adjustment screw was not really guided, and was wobbling around, and depending on the actual position, it hits the switch earlier or later.

I used a cable shoe, soldered some wire in, placed this under one of the  scres holding the the z-axis spindle screw, and wound the wire around the z-axis adjustment screw. Now the screw is guided and has a fixed position. Now I did get a reproducible  z height, that changes now only +-0.02mm. This is fine I think, and I will level the Printer now, and see if it gets now reproducible 1st layer.

refer to attached photos.

Guido

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