Acrylatic glass (PMMA) and IR sensor

[Captain_sq]

Hi,
I'm experimenting with an uncommon build plate material - PMMA. It has good adhesion properties with PLA, almost too good. The plate is 3 mm thick and is heated to about 45°C which is more than enough to make PLA stick. I get inconsistent readings from the IR sensor at various places. The surface it rests on is painted matte black but I'm wondering if it would have been better to paint the rear side of the PMMA plate itself.

Now, is it the black surface under the PMMA plate that reflects the IR signal or is it the top surface of the PMMA?

[dc42]

When using a bed material that is transparent to IR, the aim is to have as little reflection from the rear side of the bed as possible, so that the reflection from the top surface dominates. That's why I advise using a black surface underneath. If the sheet is glued down to the heated plate, then you need to paint the underside black before applying the glue or adhesive sheet, otherwise the adhesive will reflect too much.