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I just discovered automatic bed leveling (ABL) probes that only use a microswitch.

For example, the FreeABL as shown below:

Photo of a FreeABL installed on an Ender 3

Source: Thingiverse.com

Or, the magnet mounted KlackEnder as shown below:

3D rendering of a KlackEnder bed leveling probe

Source: Thingiverse.com

Both use the simple concept of probing the bed using a microswitch instead of an optical or retractable touching probe, such as the popular BLTouch. However, since no measurement other than touch can be made, how reliable and accurate are such methods? Did someone ever run a Probe Repeatability Test (M48) for such microswitch based automatic bed leveling probes, or have experience regarding its reliability?

For reference, a 10-probe M48-test using my CRTouch results in a deviation of 0.000750.

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    $\begingroup$ My printer used these for Z homing before I added a BLTouch. Anecdotally, the first layer thickness reproducibility was not great, although I never did any numerical tests. Ironically, the little lever arm actually increases the inaccuracy. It magnifies the motion of the actual clicky button, so it magnifies its trigger point tolerance as well. Again, no data, so just a comment and no answer, sorry. $\endgroup$
    – Fritz
    Commented Dec 7, 2023 at 8:56
  • $\begingroup$ I have come across this on the internet, just search and you will find. The microswitches are indee not very reproducible. $\endgroup$
    – 0scar ♦
    Commented Feb 4 at 15:56
  • $\begingroup$ @Fritz: You're supposed to remove the metal lever arm when using them, for exactly the reason you mentioned. $\endgroup$
    – R.. GitHub STOP HELPING ICE
    Commented Feb 4 at 16:14
  • $\begingroup$ @R..GitHubSTOPHELPINGICE Yeah, that's what I thought, but then (A) why are they there in the first place and (B) why are there so many printers out there with the lever arm in place? Granted, my printer was a cheap chinse i3 clone... (also, it's in the photo in the question above :D) $\endgroup$
    – Fritz
    Commented Feb 4 at 22:04
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    $\begingroup$ @Fritz: I was talking about X/Y homing where you don't care about reproducibility unless you're trying to resume a failed print. For Z, having the lever there is indeed dumb unless you're re-probing anyway (then why not just use probe-as-Z-endstop?) and just want to get the Z homing 'close' (maybe to use with a quickdraw that needs Z close to pick up a probe from a dock?) $\endgroup$
    – R.. GitHub STOP HELPING ICE
    Commented Feb 6 at 15:24

1 Answer 1

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I use them both for my Ender 3 home-against-bed and for my delta-calibration probe, and they work reasonably well. Of course, as noted in a comment by Fritz, you should remove the metal lever arm, as that amplifies any error, as well as introducing its own non-reproducibility through arm stiffness that may vary with temperature.

I forget the actual spread of values I get probing my delta, but my Klipper probe configuration has samples_tolerance set to 0.015 mm, meaning that, when it probes each point 5 times, it will start over if it gets measurements that differ by more than that amount, and normally it does not restart. However, with it previously set lower (probably 0.005 mm but I don't remember for sure), I did on occasion hit instances of it repeatedly failing. So, in my usage, it was repeatable with an error margin of something greater than 5 microns but less than 15. I don't think that's too bad.

The particular switch/PCB I use was a cheap generic "Ender 3 endstop switch replacement" off Amazon.

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