IR sensor by dc42 and Kapton covered glass

  • Hi,

    I completed the "Duet-ification" of my Replicator 2x recently.
    After quite a bit of tuning etc. it is now printing like a champ.

    However one issue I was not able to solve: the IR sensor.
    While it is installed and sensing fine I have issues with the variance in trigger height.

    My built surface is borosilicate glass on top of an aluminum heater bed.
    As there are issues with aluminum reflections and the IR sensor as I understand from the blog, I have painted the aluminum black (BBQ black paint).
    In addition I also painted the bottom surface of the glass black (the area that touches the heater). The top of the glass is covered in kapton tape.
    Before I painted the bottom of the glass black I got trigger distances of 1.90 mm, after that it went up to 2.4mm. As I had trouble with ABS sticking to the tape I applied a bit of ABS juice (very very diluted, just makes the Kapton a bit cloudy) and the trigger distance went to 2.58mm.

    From this I take it that the trigger distance changes heavily with the state the surface is in resulting in quite a bit of variance (e.g. after I pull a piece off and the ABS juice cloudiness is gone, I typically get failed first layers as the distance to the glass is wrong). Running meshbed compensation does not look to flat either making me not trust it (doubt that the glass plate has 0.2-0.3 delta at certain places).

    Any suggestions how I can get this to become more reliable?

    Thanks a lot,

  • I had similar issues with using 3DLac on my glass plate. It seems that it changes the reflectivity of the surface depending on how thickly it is applied. So, with black painted glass it will be different but consistent and you can set the Z offset to suit. With Kapton tape, it will be different but consistent, so again you can set the Z offset to suit. With ABS juice or some other liquid applied to the glass or tape, it will change and in an inconsistent manner both between applications and across the surface.

    Which basically leaves two options. Either stop using ABS juice or change to a non optical type of Z probe.

  • administrators

    An opaque surface is ideal for the sensor and gives the maximum trigger height. The more transparent to IR the bed surface is, the more the reflection from the back of the glass (and anything underneath it) will reduce the trigger height. On my (long) list of things to do it to try black glass as a target for the IR sensor.

  • Ok. Thanks for the reply.

    Not sure what to do. I could go back to the fixed z endstop and adjust the build table manually or maybe go with a pei sheet on the glass to keep it consistent as kapton alone is not ideal for keeping abs securely fixed (hence the need for abs juice).

  • Paint the top of the glass and apply PEI. Prints will stick and the trigger height is much better less variance.

    Or give the black Polycarbonate bed with no heat a try.

  • Thanks for the tip. Went back to fixed z height for now till I have sorted the bed surface out. Pei sounds interesting

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