Yet more questions, initial layer height?

I’ve spent a lot of time doing maintenance on my two year old Mini. Replaced the PEI sheet today. Leveled the Z-axis. Currently printing with Polylite PLA whit has an initial layer height setting of .25mm. I’m measuring .40mm with the current Z offset of -1.50. Should I reduce the Z offset until I get a 2.5 mm layer height?

The initial layer height in Cura is set to be thicker than the rest of the layers, this is to help with bed adhesion. If the first layer is thicker than the rest in your print it is nothing to be concerned about. However if you wanted to adjust the first layer to be as thick as the rest, you could do so through the quality settings of Cura, then you would also want to lower your Z-Offset to help compensate for the change and make sure your print stays adhered to the bed.

Are you doing the z-offset through CURA (aka in the gcode) or on the printer? If you are setting this up on the printer, then you shouldn’t have to do extra work in CURA to adjust for that because those changes were made hardware side.

All the z-offset does is makes sure that first layer goes down at the expect height so you don’t have, for instance, filament dragging behind the head instead of adhearing to the bed right away.

That being said, the best way I have found to calibrate my z-offset (which thank heavens I have gotten perfect) is to print a Rocktopus model (the one Lulzbot gives everyone, because it’s a valid, and clean model, and should print clean, with no weirdness). Upon completion pop that baby off the bed, check the bottom of the print. Is it a smooth sheet w/ no lines? if so, you are good, but if you can see lines, it’s too high, and you need to drop it down (I think you want to get a larger negative number if memory serves me right). See the image below for what a good first layer should look like. As someone put it, it’s almost “smooshed” on.

MAKE SURE YOU DO SMALL CHANGES to risk not driving the head into the bed

By the way, I think this is the right link that shows tips on this
https://ohai.lulzbot.com/project/z-axis-offset-adjustment-LulzBot-Mini/maintenance-repairs/

(Side note, I have literally 10-20 Rocktopus models doing this just laying around)

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Wow! I have my work cut out on getting initial layers looking that clean.