Bad adhesion - faulty sheet?  

New Member

Hi all! So by this point I have assembled 5 MK3S printers. The first one was my own and the later ones were for a university society and my employer. With my very first one, I had an issue with awful adhesion on the flat sheet, where PLA would not stick, no matter how much I'd clean the bed with IPA, and ultimately only worked with glue. This was however not repeated on any other printer I have made. Today I have attempted to use a different flat sheet on my original printer, and it worked flawlessly.

Not really a question as such but this leads me to believe that some sheets can be faulty with awful adhesion. Is this a known issue? Are there any other good solutions because obviously my one is a hack rather than a solution?

Posted : 17/09/2020 6:34 pm
Prominent Member

Yes, there's evidence that some sheets do stick better than others, but mostly this is reported with the textured sheets.

There's also some evidence that sheets work better after they are 'seasoned', as in used a bit, kind of like a cooking utensil.

One thing I might try is acetone, as that is said to somewhat 'refresh' the coating on the smooth sheets.

Posted : 17/09/2020 7:32 pm
Illustrious Member

Here's my standard suggestion for bed adhesion issues:

If it's a smooth PEI sheet, take it to the kitchen sink and give it a good dunk with Dawn (original formula, no vinegar or hand softener variants) dishwashing soap or your local equivalent (e.g. Fairy in UK). Use a clean paper towel to clean it off, and another to dry it. Avoid using any sponge or cloth that has been in contact with grease. Above all else, avoid touching the PEI print surface. Once it's good and clean, you should be able to use 91%+ isopropyl alcohol between prints, 100% acetone when that fails , and another dunk when acetone fails. Worst-case, use a 3M 7445 ScotchBrite pad or equivalent on smooth PEI to give it a very light buff, but only infrequently.
Remember that the effectiveness of a solvent such as isopropyl alcohol is going to depend on concentration and volume relative to the amount of grease you're trying to remove. 71% pads work... on very tiny amounts of grease. A squirt of 91% works better, but if there's a lot of grease, you need a lot more alcohol. This is why the wash under the sink with Dawn is so effective: There's a much larger volume of Dawn and water (the universal solvent) rinsing stuff away instead of just moving the broken-down grease molecules around.
You can always try adhesion enhancers, but I'd go through this list first. The PEI sheet should hold filament well while heated, then release easily once cooled. It's possible yours was mishandled during packaging or shipping as it only takes a slight amount of grease to foul the PEI. I've found that non-Prusa sheets will often release an orange-ish coating when wiped with acetone. Getting a good, bare PEI surface is key.
A bit of trivia - The reason higher concentrations of alcohol seem to be harder to find is that isopropyl alcohol is most effective against bacteria at roughly a 71% concentration. A bit of distilled water helps slow evaporation, making the alcohol more effective. If you're looking in pharmacies, that's why 91% and higher seem to be hard to find.
My notes and disclaimers on 3D printing and miscellaneous other tech projects
He is intelligent, but not experienced. His pattern indicates two dimensional thinking. -- Spock in Star Trek: The Wrath of Khan...
Posted : 17/09/2020 8:49 pm
Prominent Member

Around here, the 91% isopropyl was hard to find in the early summer and is hard to find again.

However, I've been using the 99% 'technical' (translated: not for clinical use) grade isopropyl, which is comparatively easy to find.

What's known as denatured alcohol here in the States is also easy to find.  It's ethanol with adulterants to make it unsuitable for drinking.

This post was modified 1 month ago by jsw
Posted : 18/09/2020 12:17 am

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