I've had some issues with PEI printbeds not consistently sticking to prints,

3D Printing
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I’ve had some issues with PEI printbeds not consistently sticking to prints, but there’s an easy fix and full reset option!
https://www.youtube.com/watch?v=DzaPFlEKP10

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Using technical alcohol before every print, some windows cleaners under PET or ASA (weakens the adhesion a bit) etc. @Josef_Prusa 's team has its own guide for different materials on PEI which is worthy to follow: http://www.prusa3d.com/material-guides/
http://www.prusa3d.com/material-guides/

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I’ve found the same processes work well for maintaining BuildTak sheets. Nice guide.

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There is an issue of my printing… The printbed is frosted, the object stick too fastness to removed even with scrape or knife… Any optical way?