Etched/Cut Through/Damaged PEI

During a recent print the mini made a horrible chattering noise during bed leveling. As the printing began, I noticed that the nozzle was actually etching/cutting through the PEI on the build plate. It has bubbled and buckled away from the glass. Not sure if the underlying glass plate was damaged.

Can I remove the PEI? Does this need to be replaced with a new sheet of PEI, or can I use something like painters tape?

Not sure how this happened, but I would like to get the mini back in working form as I love using it and have had it in operation nearly every day since it arrived. It is great and it was heart breaking to see the damage! :cry:

Greg

You should contact support. Removing the adhesive that holds the PEI on is apparently a major headache.

As for why it happened, probably there was a little bit of plastic filament residue on the tip of the nozzle. The leveling works when the nozzle touches the washer and completes a circuit. The Z height where that happens is stored and the leveling calculations make use of that stored value. The key is that the Z axis keeps decreasing until the circuit is closed. The plastic on the nozzle acted like an insulator and the prevented the circuit from closing the moment the nozzle touched the washer. So the Z axis kept going down until it got a reading, which made the computer think the Z axis was lower than it really was. When the print started, the nozzle was pushed down to that too-low position and gouged the bed.

I made the same mistake more than once as I was learning to use my mini. Make sure your nozzle is as clean as possible. The mini auto-levels every time, and to do that it passes a minute electrical current from the nozzle tip to each washer on the bed, noting its Z axis location as it does. If your nozzle has plastic on it, then the electrical current wont flow when it needs too, meaning the nozzle just keeps pushing, producing a terrible sound. when the print starts, the nozzle pushes deep into the PEI sheet and tears it up.

Purchase a new PEI sheet from the lulzbot website for 25 bucks, and use the knife that came with your printer to carefully remove the PEI surface. Use glass cleaner or some other cleaning solution to painstakingly clean the 3M glue off the glass, then carefully apply your new PEI sheet and keep a close eye on your printer EVERY time you start a new print.

Thank you both for your replies and advice. This is the precise scenario. The print head was very dirty and must have been insulated from the electrical contact on bed leveling. I got so used to the mini printing without any flaws/baby sitting that I felt comfortable clicking Print on Cura and walking away. . . Lesson learned, -$25.00 + shipping & labor! :wink:

Other removal tips for PEI and its adhesive:

  • Remove the bed heater/glass/PEI and freeze it for 30 minutes or so to make the PEI much easier to peel from the adhesive
  • GooGone is great for dissolving the adhesive- let it soak in per the instructions. Use a straight razor to scrape off the adhesive. Typically it takes at least two soak/scrape cycles to remove it all. I’ve heard some aerosol window cleaner/ bug removers are even better, but haven’t had time to figure out which ones work.