Sounds like you have the Mk2 figured.
The Mk3 probably just needs a recalibration but there are a couple things worth noting:
- Last I saw the sheet was caked in dust, I assume you gave it a good and thorough clean with IPA (rubbing alcohol, not beer).
- Make sure you are using the correct sheet for your material: if it's PLA/ABS use the smooth sheet, if it's PET/PETG then ONLY use the textured sheet (PETG will stick way too well on the smooth sheet).
- In the home menu select the sheet settings to match (Smooth1 or Texture1). This lets you set different First Layer Calibration settings on the z-axis to match each sheets thickness.
- You can try just doing the 1st layer calibration but I'd recommend the XYZ first.
- Run a new full XYZ first layer calibration. This should be performed periodically, takes like 10 minutes.
- Then run the first layer calibration and get it dialed in.Prusa's guide gives you the goods.
- The smooth sheet has seen a LOT of use and could use a fresh layer of PEI.
- The sheet is double sided so you can always try both.
- The center of the bed will be the most worn, easy solution is to move your print over to the side when slicing.
- The right hand side of the bed has only one support bearing down the middle, where as the left side has two. Because of this the front and back right corners of the bed have more flex and generally won't stick as well.
- Run a new XYZ first layer calibration. This should be performed periodically, takes like 10 minutes. Then run the first layer calibration and get it dialed in.Prusa's guide gives you the goods.
EDIT: Also worth nothing Mike and I did a big rebuild on the extruder head and the wear components on it were replaced, with every fastener on the entire machine retorqued. So in general it's good.
I can't remember if there is PEI replacement sheets in the spare parts, I thought I ordered one but my receipts say otherwise. There is a brand new steel PEI sheet that belongs to Makerspace that is destined for the Mk2 upgrade however. That could be used if you really can't get stickage to happen.
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