Model originally uploaded to Thingiverse at https://www.thingiverse.com/thing:4804130.

The ideal position for an ABL probe is obviously at the nozzle.  But probing with the nozzle has its own problems: when hot, the nozzle could damage the bed and when cold, there might be plastic offsetting the position triggering the probe ...

So, the next best thing would be a probe as close as possible to the nozzle, but that's easier said than done ... or is it?

Presenting the Near Nozzle Probe.  The idea is simple: use a metal "needle" to get as close as possible to the probe, but move out of the way during printing (and away from the heat).  The "detection-unit" is an optical end-stop and is moved sufficiently up - away from the rotation axis - to avoid too much loss of accuracy with the long distance from the needle point to the rotation axis.  That axis uses 2 MR115 bearings, but more on that below.

To move the needle up and down a 3.7g SG37 servo is used and the needle used to be a paper-clip, now bent into the position wanted.  It is fixated into the arm by heating it up using a soldering iron - ideally including a 90° angle touching the arm side to prevent it from rotating (see youtube movie).  And everything is bolted shut using M3 20mm and one M3 30mm bolts (as those is what I had around).

Now, despite the bearings, gravity was not enough to "deploy" the probe reliably, which is why the servo doesn't just have a deploy and stow position, but also a measure position, i.e. the deploy angle pushes the needle down, then the servo moves back so that the needle has room to be pushed back up when pressing against the bed.

But as far as I could tell, Marlin only supported 2 states for a servo probe, so I had to add some support for the extra "measuring angle" and because I want to have the needle retracted while moving (to avoid hitting something), also added a Z_SERVO_INTERMEDIATE_STOW setting for that.    The changes I had to made can be found on [github](https://github.com/MarlinFirmware/Marlin/pull/21427/commits/407d2e0f61d28698edcde5146c6c56858983b137).

With everything put together, we get a pretty decent standard deviation of 0.002693 mm without moving X and Y as seen in this [Youtube movie](https://www.youtube.com/watch?v=1wUFTY2nHnQ) and the `M48 S1 P20 V4` test results in a decent:

```
Mean: 0.003375 Min: -0.005 Max: 0.013 Range: 0.018
Standard Deviation: 0.005550
```

This was with the needle bent so it ends behind the nozzle, giving me an offset of:

```
#define NOZZLE_TO_PROBE_OFFSET { -4, +12, -2.8 }
```

So, using Pythagoras, this means we're probing at 12.6mm from the nozzle, not too bad, right?

So, is this probe better than others?  Time will tell, but it's definitely good to have options and to allow everyone to build on this and try to improve it, I have included the Fusion 3D design.  Feel free to analyze, modify, extend and otherwise use it, but when you do publish something based on it, please just gimme a bit of credit ;-)

NNP Near Nozzle Probe

Model originally uploaded to Thingiverse at https://www.thingiverse.com/thing:4780326.

I had so much problems with my 3D Touch that I decided to create an alternative.  Several designs exist combining an optical endstop and a small SG37 servo, but they typically were too wide for my taste and I wanted the probe point to be as close as possible to the nozzle - if possible only offset in one of the main directions.

The result is this design.  It has offsets of (-40, 0, z) where z depends a bit on how you mount it.  My mount isn't ideal, but I'm sharing the Fusion 360 file for those wanting to build on this.

The M48 probe test with parameters L3 P25 S1 V4 yields (full results in included file):
>  Mean: 0.011500 Min: 0.005 Max: 0.015 Range: 0.010
>  Standard Deviation: 0.002915

This might not be the best probe ever, but it's way more reliable than the bad 3D Touch that I had and with a range of 0.01mm over 25 probes should be more than enough for good bed adhesion.

I have included the 3MF file I used with PrusaSlicer to show how I printed it without supports.  You obviously do need an optical endstop, an SG37 servo and some M3 (countersunk) bolts and nuts.

OptoServo Probe

Model originally uploaded to Thingiverse at https://www.thingiverse.com/thing:4931832.

This idea isn't new, but I did create the design from scratch to suite the M3 nuts and bolts that I have available and the bearing.  The main idea is that a simple switch detects the presence or absence of the filament, but because of the filament path too much tension on the filament (when there is a jam) will also pull it away from the switch and hence trigger a run-out.

The spring is just from a simple pen and might not even be required if you tension the bolt holding the arm sufficiently.  After the jam detection goes off, you might have to manually press the arm manually back in place, but you anyway need to resolve the jam in that case.  This design is working very well on my Ender 3 Pro (older iteration) and my Sapphire Plus (the iteration included here).

The printed bushing is used to fit the 608zz around the 20mm M3 bolt going through the center of the arm.  You add a standard end-stop button (not a full end-stop module, just the switch - one with a metal bar that's bent in half a circle at the end) between back body and front (and if you want to use a spring, also an M3 nut where the bolt holding the spring would go) and then bolt those tightly together with some 10mm M3 bolts - except for where the arm should get attached.  There you first put the arm on and then tighten everything together with a 20mm M3.  Depending on the tension wanted, you can add a spring and M3 bolt near the front of the arm.  Add a washer between spring and arm to avoid it goes in the slit of the arm.   The arm doesn't have to move up too easily, but should be able to open up when the filament tension becomes too high due to a jam.

Then finally you can add 2 PTFE tube couplers with 6mm threads.

No supports should be needed and printing should be fairly easy.

Filament Run-out and Jam Sensor

Model originally uploaded to Thingiverse at https://www.thingiverse.com/thing:4717893.

Mount LEDBERG way above where the printhead of the Ender 3 gets ...

As I converted my Ender 3 Pro to Direct Drive with a simple 3D printed bracket mounting the motor sideways in such a way that you don't lose any build-volume, I also didn't want that motor to run into any LEDs at the top of the printer.  The LEDBERG mounts that I could find were typically just placed at the same height as the top 2020 extrusion of the Ender 3 and would be hit by my Direct Drive conversion.

So, I created this simple bracket to mount all 3 LEDBERG bars (connected with custom-made power connectors - exactly what IKEA says you should not do of course).  The bottom should tightly fit in the V-Slots of the 2020 bar.  I printed 2 of these brackets to hold the LEDBERG bars at both ends, but you might get away with a single one or can add extra if you want things to look more robust.

LEDBERG mount for 2020 (Ender 3)

Model originally uploaded to Thingiverse at https://www.thingiverse.com/thing:4598713.

Q: Why another filament sensor?
A: Well, why not?


Q: What is wrong with a simple limit-switch one?
A: Nothing.  But if you need something else that adds very little drag on the filament and is dimensioned differently than a limit-switch, then this might be useful ...


The metal piece of a limit-switch is basically a spring and springs have the "feature" that the force they push back with increases as you push them away from their normal position.  For a filament sensor that typically means that the limit-switch will be pushing your filament against a wall of your sensor body, causing drag en possibly erosion over time.


Magnets are like inverse springs: the force they exert gets lower the further you move the magnets apart.  In the design here you can feel this very well: you feel the effort it takes to pull the magnets apart to get the holes - lined with PTFE tube - to align and allow the filament through, but when those holes do align, the magnets are so far apart that the force they exert is still sufficient to get them to move back together if there is no filament connecting the holes, but causes barely any drag on that filament ...


When printed in the provided position, no supports should be needed and the entire sensor prints as one.  The second part is a mount, again not requiring supports in the given position.  I do suggest using a raft (2mm extra sticking out under the part should be enough) to avoid that elephant's foot fuses the moving arm and body.


Once printed, there is some extra work to do:


1. Prepare 2 cylindrical 5mm diameter magnets (around 2-3mm thickness), by soldering a wire to each of them.  The wire diameter including insulation should be less than 2mm.  The wire used for the moving arm should be very flexible to avoid that it stops the arm from closing.  This is also the reason for the somewhat weird wire path.


2. Rotate the arm so that you have access to the hole for the PTFE tube.  Insert a piece of PTFE tube into the hole and use a cutter to cut it flush with the arm.  Then do the same for the PTFE holes at both side in the body.  Make sure that you do not push the PTFE tube in too deep: the arm should be able to move freely.


3. Take one of the magnets with the wire soldered to it.  Insert the free end of the wire through the diam. 5mm hole of the main body, bending it so that it goes into the small 2x2mm hole moving it out through the bottom.  Then push the attached magnet into that hole as far as you can (but don't overdo it).


4. Take the second magnet and again push the free end of the wire through the hole from the bottom of the arm up towards the "ditch" that can hold this wire.  Then push the magnet into the opening in the arm.  Lead it in this "ditch" under the "finger tip", turning around and then to the bottom of the arm, ending close to the other wire.  As said, the intention of this path is to allow the arm to move as freely as possible despite this wire.

Mini Filament Sensor

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NNP Near Nozzle Probe

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Filament Run-out and Jam Sensor

LEDBERG mount for 2020 (Ender 3)

Mini Filament Sensor