mhackney wrote:Read my looooong thread on PEI - it has a lot of info on the 3M adhesive and various techniques to apply it. viewtopic.php?f=36&t=7452
Does the 'wet' application really work with the 3M adhesive? Just making sure I don't bugger up a $20 piece of PEI.
I have more sheets coming from Amazon after falling in love with my first sheet. But this time I'm not going to use glass, I purchased four 0.125" aluminum plates from a local supplier for $10 per plate cut to order from an industrial sized sheet of 6061-T6. The PEI is going right on top of the Al plate and I hope this cuts down on the loss of heat from the Onyx. I don't see any distortion in the flatness of the plates when checking with metal straight-edges.
Currently I have a thin surface thermocouple taped to the back of the Onyx in the center well near where all the cables solder on. This gives me the temperature of the back side of the Onyx so I know what my thermal fuses are seeing. I was surprised to see a 10 degree difference between the thermocouple and the thermistor, and another 15-20 degree difference between the thermistor and the surface temperature of the PEI. The glass, adhesive and PEI are not great conductors of heat. Hopefully the Al plate will help get the heat from the Onyx to the PEI and reduce the temperature drop on the surface. The enclosure is also helping lower the temperature drop between the Onyx and print surface.
Another funny thing I saw was the bed height changing while the bed was heating up. I manually ran the effector down to Z=0.5 mm and used feeler gauges as the bed heated up. The bed height swelled over 1.0 mm until it came to temperature where it settled back down. If I had a run-out dial indicator handy I would take a video of the dial to show it better. The good news is that this explains why I was having first layer troubles with the PEI at first because I was starting my prints too soon after the bed reached temperature. I don't know if the swell is due to the PEI-glass interface or to the glass warping or something else. If I wait 5-10 minutes after the bed comes to temperature to start a print I don't have the first layer blues.