Cleaning the PEI flex steel print sheet for proper adhesion

The Prusa i3 Mk3 printer is configured with one of two versions of a PEI spring steel print sheet.

  • Prior to April 2018, the Mk3 could be ordered with a double-sided powder-coated textured PEI-coated spring steel sheet. This option was withdrawn from sale until backorders could be filled (still in progress as of May 2019), at which time Prusa plans to offer them for sale.
  • A double-sided smooth PEI stickers on a spring steel sheet. This is the options currently shippping with new orders.

PEI has excellent adhesion properties for most materials, but does require some basic maintenance. Without good first layer adhesion, you’re going to have a difficult time achieving good print results. It’s worth spending some time getting familiar with the bed characteristics when starting out.

Note

These notes are based on my experiences with the Prusa i3 Mk3 printer. If you are using a different printer, please verify the hardware details are same. These pages may be a bit rough as I revise them and add new material. Please check back regularly for updates.

The riddle of adhesion

You’ve probably seen some of these guidelines before, and may have wondered exactly why these simple sounding steps work. Here’s an unscientific breakdown.

  1. Isopropyl alcohol [3] and acetone [4] work as solvents [1] , breaking apart grease molecules. Consumer-grade cleaners do not completely dissolve grease, but do break it down far enough that it can be removed from surfaces easily.
  2. The more concentrated the solvent, the more effective it will be at a given volume. Those little 70% isopropyl wipes do work… on a shiny new PEI sheet. They’re just not effective dealing with larger amounts of grease. This is why 91%+ alcohol is recommended. Acetone is even more effective, but can make the PEI surface brittle over time.
  3. The amount of grease that any solvent will effectively break down is directly proportional to the volume of solvent to grease. The more you apply, the more grease it can effectively break down.
  4. Alcohol, acetone and any other solution you apply directly to the bed is just going to move those broken-down grease and grime molecules around. Some will be picked up by wiping with a clean towel, but some will remain on the PEI sheet.
  5. The reason a wash with Dawn is so effective is not because Dawn is “stronger”, but because there’s simply a much greater volume of Dawn and water, and the broken-down grease bonds with the Dawn and is washed away from the PEI sheet. Dish soap is a surfactant [2] , not a solvent. It works in a fundamentally different way, interacting to bond both grease and water to wash away contaminants.
  6. Windex, a wipe of finger grease, talcum powder or specialized release agents can be used to reduce adhesion when using hot, sticky materials that grip the PEI surface too firmly such as PETG.
  7. If you are printing high-temperature materials (e.g. PETG at 260C on a 90C bed), test to make sure it will release once cool without damaging the PEI surface. You may want to use glue stick or other release agents for these materials. Test on a sacrificial PEI surface if possible. See over adhesion, below.

A touch too much

The other under-appreciated problem with adhesion is how much simple handling of the sheet contaminates the surface. While you may be careful handling your sheet, there are very likely times that you touch the surface without thinking about it. How are you removing prints?

  • Do you remove the sheet to flex it?
  • Do you grip the sides of the sheet while popping parts off?
  • Do you brace the side of sheet with your hand while removing parts?

If so, you are introducing grease at least at the edges. This would not be a problem, but the next time you wipe the bed with isopropyl alcohol or acetone, you may be inadvertently wiping some of the broken-down residue onto the print area.

I made a test run in which I concentrated on not introducing grease onto the PEI surface. I held the flex sheet exclusively at the edges, only printed on one side and used a plastic scraper to remove printed parts, skirts and prime lines. With a bit of care, I was able to get well over a dozen solid prints without adhesion problems with no additional cleaning.

Note

IANAC - There’s a lot more chemistry and magic to this if you care to do a deep dive. I am not a chemist.

Cleaning the PEI print surface

Note

Whether you have a textured powder-coated sheet or the version with PEI stickers, adhesion and cleaning procedures are the same.

Under normal circumstances, your cleaning routine should be as simple as:

  1. Give the bed a thorough clean with 91%+ isopropyl alcohol. Not necessarily every print, but any time you think you might have touched the sheet or otherwise contaminated it. Weaker strengths of alcohol may work, but stronger concentrations simply do a better job of dissolving grease at the same volume, so you can use less. The goal isn’t to wipe the alcohol around like you would if cleaning a window. We want to move grease off the print surface. Apply a generous amount of alcohol to the center of the bed. A wash bottle dispenser can be handy for this purpose. Wipe outwards, moving any accumulated grease to the edges of the PEI and away from your active print area.

    Applying isopropyl alcohol for PEI surface cleaning

    Fig. 43 Applying isopropyl alcohol for PEI surface cleaning

  2. If isopropyl alcohol fails, try a clean with 100% acetone. Acetone is a stronger solvent than isopropyl alcohol, so may deal with larger amounts or stuck-on grease better. This isn’t recommended every print because it can eventually contribute to cracking of the PEI, but it rejuvenates the PEI surface. Consider a wipe every month or so for conditioning.

  3. If isoproply alcohol and acetone don’t work, there’s a good chance there’s enough build-up of gunk that you’re simply moving it around. Take the sheet to your kitchen sink and give it a good was with Dawn dish soap or your local equivalent. Use a clean paper towel to clean it and another to dry it. Avoid touching the PEI surface after cleaning. Seriously.

  4. Finally, all else fails, you can try a buffing with a 3M 7445 Scotch Brite pad. Rub gently, roughing up the surface slightly without digging in or removing any PEI.

Scuffing the PEI surface with a 3M Scotch Brite 7445 pad

Fig. 44 Scuffing the PEI surface with a 3M Scotch Brite 7445 pad

Above all else, avoid touching the PEI surface. With a good clean and a proper Live-Z calculation, you should have no problems with adhesion. If you’re careful, won’t need to clean the bed every print.

Cleaning materials

The materials you use to clean with can be as important as the solvents and soaps. Using a used dish rag or sponge can deposit grease onto your PEI surface.

  • Use a clean plain paper towel if nothing else is available. Avoid any products with skin softening agents, scents, or other additives.
  • Blue low-lint paper shop towels are more durable.
  • Prusa suggests using plain paper coffee filters as an alternative for quick cleans.

Dealing with over-adhesion

Some materials like PETG grip a bit too well to the print surface. If printing with these materials, you want to use something to lessen the grip. Prusa recommends the following:

PETG and other sticky materials

For “normal” sticky materials, you need to use something to loosen the adhesion.

  • A wipe of the PEI surface with Windex or your local equivalent of window cleaner will work. Don’t use anything enhanced with vinegar or anti-streaking agents. The key is that this cleaner leaves a very thin residue that helps remove materials that otherwise stick a bit too well.
  • Simply wiping the print area with your fingers can work well. Not too much, but enough to interfere with the adhesion.

High-temperature PETG and other specialty materials

For high-temp sticky materials that print at 240C and higher, you may need a better relese agent.

  • A thin layer of glue stick on the print area will help pop parts off. You don’t want to use too much, and it will eventually build up and require a good cleaning under the sink (see above).
  • I’ve had good luck using MagiGoo on the PEI. The applicator allows applying a precise thin layer exactly where it’s needed. It’s still a bit messy and requires eventual clean-up, but not as bad as glue stick. MagiGoo is a bit expensive, but a small bottle goes a long ways.

Here’s a “lessons learned” advisory, showing both the damage and subsequent attempt at patching my original PEI sheet after printing high-temperature PETG without sufficient release agent, and the same part and material printed on the same surface with a coating of MagiGoo.

Over-adhesion damage and mitigation with MagiGoo

Fig. 45 Over-adhesion damage and mitigation with MagiGoo

Part removal

Finally, take advantage of the removable flex surface to pop prints off. You can use a non-metallic scraper to help lift prints that stick a bit. iomaa’s printable removal wedges are handy for removing completed prints without touching the PEI print surface.

Removing stuck-on parts with a 3D printed scraper

Fig. 46 Removing stuck-on parts with a 3D printed scraper

Footnotes

[1]Wikipedia article on solvents
[2]Wikipedia article on surfactants
[3]Wikipedia article on isopropyl alcohol
[4]Wikipedia article on acetone

Contact and feedback

You can find me on the Prusa support forums or Reddit where I lurk in many of the 3D printing-related subreddits.

Last updated on 20190517