Inductive ABL sensor setup

It's easy to crash your precious nozzle if the ABL sensor is not setup well, and an inductive ABL sensor can only be triggered by metal objects. This guide shows how to:

• Setup the Z optical endstop

• Setup the inductive ABL sensor with a non-metal PEI sheet

• Fine tune Z parameter of G31 command

• Do auto bed tramming

Please note this approach won't work if the non-metal layer above the metal layer is too thick, for example, a borosilicate glass is placed on top of the aluminum bed. Please use BLTouch for a borosilicate glass.

Secure bed from falling

During sensor tuning the 3 bed brackets might be at different heights, or even go in opposite directions. Be careful! the whole bed assembly might slide out of kinematic mounts and crash heavily.

Tie the bed to bed brackets or shut the printer down anytime you expect a bed falling.

Auto Bed Tramming might still crash

If the bed tilt too much, it will be lifted by the corner of bed bracket, or the nozzle will crash before sensor triggered. So you must manually pull the 3 brackets to about the same height and let auto bed tramming do the fine adjustment.

Adjust sensor height

1. Move the bed away and simulate the bed with a metal object such as a wrench or a flat head driver. When a metal object is closed enough to the sensor, i.e. less than the distance between sensor head and trigger point, the sensor tiggers and the LED dims.

2. Adjust the height of inductive ABL sensor, so the nozzle is between sensor head and trigger point, as shown in the picture.

(Optional) Adjust endstop finger

Ignore this if you choose scheme <A> for Z endstop in the Wiring chapter in SK-Tank Assembly Manual. This is for scheme <B> only.

As shown in the picture, move and fixate the Z trigger finger upward, so when the endstop triggers, there is still a visible gap between the nozzle and the print surface.

This gap distance will be the parameter in G-code command G31.

Fine tune G31 Z parameter

The G31 Z parameter stands for the Z value of trigger point with the assumption of sensor and nozzle are at the same height.

But in practice the sensor and nozzle are at different heights to prevent the sensor from scratching the prints, and, the object that triggers the sensor is not necessary the nearest printing surface, therefore we need an approach to find a value which won't crash the nozzle, and acts as if the nozzle is sensing the printing surface.

In this example we assume there is a PEI layer above the steel sheet which actually triggers the sensor. Once the sensor is triggered there is still a 0.85mm gap between the nozzle and PEI layer.

We don't know the actual distance 0.85mm and have to find it out.

An approach is to start guessing the distance (Z param in G31 command) from a small number and iterate larger and larger until the nozzle just touches the surface.

With RepRapFirmware please find the G31 command in config.g file.

1. Try a Z value in the G31 commands in config.g

2. Run bed.g with G32 command or a menu button.

3. If the bed tilts too much, one time of bed tramming won't make it level. Do G32 again.

4. After the auto bed tramming is complete, move the nozzle in small steps (0.1mm or 0.05mm) to the bed with G-code or Z movement button. If there is still a gap left when Z0.0 is reached, return to step 1 and try a larger number. If it will obviously crash before Z0.0, try a smaller number.

Make sure to keep enough margin and the sensor will probe 100% above metal area but not near an edge.

A piece of paper inserted between the nozzle and the surface will help you feel when the nozzle touches the surface.

Add G32 to start of G-code file

Once you find a proper G31 Z parameter and saved it in config.g, add G32 and ignore G28 in your start G-code in the slicer settings. Another G28 is in the bed.g file.