Printing on PEI for the first time

[timskloss]

It has been a while since I posted but that is because we have been busy pushing filament on lots of little projects. I have had my new v3 for almost a month now and we just hit 2000 meters total filament. So now I consider myself an "intermediate beginner". Time to make bigger mistakes!

One of the best mods I think I have made so far is installing a PEI build surface. I bought the 12x12" sheet and adhesive kit from Gizmodorks on Amzn. So that is on top of a spare borosilicate plate heated by a 24V DC upgrade. (Crydom SSR, safety cut-off relay and thermal fuses)

But now I have the dreaded "welded part" syndrome. My original SeeMe part separator spatula is now as kinked as a punk-rocker's haircut, and I have deposited a few drops of blood on the v3 that I will leave in place as a reminder in the future of how much force NOT to apply to the bed. I have tried cooling the bed outside (its in the single digits here) but that doesn't seem to make much difference.

I am impressed with the amount of force that a part places on the bed when it wants to curl. I have seen edges of large PETG parts actually lift the PEI and stretch the adhesive underneath (90C bed temp) by about half a mm. The PEI returns to normal after the part is removed, but it is impressive.

Should I expect parts to be this hard to remove? Is this the price I pay to get 'straight' large parts? Or am I just using the PEI in the wrong way?

What PEI bed temperatures would be reasonable for PLA, PETG and ABS when printing parts that are 5 inches or more long on the build plate?

The learning curve in this hobby is steep but I enjoy the challenge. And I enjoy reading all the posts to this forum. There are some really generous and capable souls in this group.

[Xenocrates]

I believe what happened here may be an instance of the z height being set too low. I might try getting a can of air (or electronics cold spray), and taking the bed up to temperature, then using the straw on the can to hit an edge (if using the can of air, invert it for maximum effect). However, be aware that this can thermal shock the bed quite a lot. Don't keep blasting it. Short pulses only, unless you feel like replacing the glass (This is part of why my PEI is on aluminum sheet). If this still doesn't help, let it freeze outside, and use a pair of pliers of appropriate size, or a bottle opener type thing to twist the part. This has often helped me.

[timskloss]

Thanks for the tip. Warm bed, cold part, and twisting. I'll try that next.

[mhackney]

Think about the physics. Twisting is not the best approach as it maintains 100% of the surface area between the 2 parts. You need to sheer the part off the PEI. This is done by getting something under a corner or edge. Once you've done that, keep working at it or blast that area with the cold air can.

I agree, it sounds like your Z=0 is too low and your first layer is really pressed into the PEI. You don't mention how you clean. Don't use acetone with PLA, it micro cracks the surface resulting in very strong adhesion. Use isopropyl alcohol for PEI and water for PETG.

I print PLA on a 50° PEI surface, ABS on 70°.

As for the bent spatula, did you read how I prepare and use the spatula here: http://sublimelayers.blogspot.com/2016/ ... o-and.html

That little bevel makes all the difference.

[TwoTone]

I'll just place joe's PM to me. My son was having the same issue getting parts off PEI. In a post Joe mentioned being on the same sheet for years. My son had gouged 2 of his in his impatience to get a part off, so I PMed Joe to ask how he gets parts off and maintains his sheet.

Here's his response:

I let the part cool for 5 minutes for small prints and usually just for a couple of minutes for larger prints, Then using a hobby hammer just give them a sharp tap, not a swing of the arm, just a quick flick of the wrist and the part just pops off with a snap. Sometime a paint scraper is helpful at the base with a sharp tap to the scraper with the hammer.
I use 600 grit wet and dry sandpaper with water once in a while to remove marks/shadows from past prints.
I only usually clean it with alcohol after sanding. Other wise a gentle scrape with edge of a razor to scrape off residue is all that is needed.

[timskloss]

I agree, it sounds like your Z=0 is too low and your first layer is really pressed into the PEI. You don't mention how you clean.

You were right, I raised Z=0 by 0.1 mm and parts come off much easier and still stick down in the corners. I clean the PEI with 91% isopropanol per the manufacturer's recommendation between each part. So far no gouges in my plate. It is remarkable how resilient the PEI is to scratching even with metal tools. This weekend I took the shine off the PEI with 320 and then 1000 grit wet sanding blocks I picked up at the auto paint shop. Like you said it leaves a nice matte finish on the parts.

So far I have only printed PETG on the PEI but plan to get back to PLA and ABS soon once I finish off the parts for my enclosure. I'll be sure to start with those temps.

[mhackney]

Did you measure the first layer thickness after printing a single layer object as I describe in my signature posts? That is a much better way to do it than guess at .1mm.

You do not need to clean after each part, I often print several dozen parts without cleaning - especially if they are all the same part. The "footprint" of the part is "prepared" by the first print and really does not require cleaning if you don't touch the surface.

[timskloss]

Did you measure the first layer thickness after printing a single layer object as I describe in my signature posts?

Yes, I set my slicer to 'first layer only' and measure it with my digital caliper. Surprisingly accurate to what was programmed. Good advice, I like this method instead of feeler gauges because it can tell you exactly what the offset correction needs to be.

If I change the Max Z height in EEPROM (Rambo) does that only affect the Z=0 location, or does it also affect other aspects of the bed calibration?