i3 Suddenly OverExtruding: ideas?

[printbus]

Clough42 - it may not be related, but there have been a few people who determined their heat bed would flex as the heater cycles on and off. That's the closest I remember anyone saying they see the Z axis changing with temperature. In those cases the varying Z-axis height led to print quality issues throughout the entire print, not just the beginning. Maybe in your case the Y-bed warms up with run time and keeps your heater flexed upwards.

Are you running with the same glass as before? Same clips and clips installed in the same place? Ambient room temperature about the same as before?

[clough42]

Oh, man...you may be on to something there!

That's a definite possibility. First layer is at 100C and subsequent layers are at 110C. I'm testing my Z height by measuring the thickness of the loops with calipers, but those are printed at 100C before ramping the bed up to 110C for subsequent layers. I should be able to test that by printing the same model with the same settings in PLA on a cold bed. It doesn't totally explain everything, but it suggests a great test to learn more.

I also noticed what looks like Z banding on my prints, but under close inspection, the layers aren't offset--some of them are just wider. The bulging layers bulge all the way around the part. That could be long-term oscillation of the bed shape due to heater cycles. I'm running bang-bang control of the bed, so it could definitely be related.

I could probably put a dial indicator on the center of the glass and just let the bed run...

And yes, the printer is in a new location, near an AC vent in an exterior corner with outside temps hitting 111F. I thought I had the air off the bed, but who knows. Worth checking.

Clough42 - it may not be related, but there have been a few people who determined their heat bed would flex as the heater cycles on and off. That's the closest I remember anyone saying they see the Z axis changing with temperature. In those cases the varying Z-axis height led to print quality issues throughout the entire print, not just the beginning. Maybe in your case the Y-bed warms up with run time and keeps your heater flexed upwards.

Are you running with the same glass as before? Same clips and clips installed in the same place? Ambient room temperature about the same as before?