Specs for replacement PEI on Mini?

I donated a Mini to a local school (a teacher there is a real tech fanatic). On the first attempt to print something with the class today, the Mini went through it’s auto-leveling sequence (supposedly normally, but I was not there to see it). When it started to print, the nozzle just punched into the PEI surface and wiggled around a bit, melting a hole in the bed. We are still trouble shooting the problem, and have just started in that regard.

I’d like to get a couple of spare PEI sheets on order. I’d prefer to go through the Lulzbot store (having the adhesive already on saves a bit of hassle for the teacher, if she ever has to replace it on her own). Unfortunately, the store says the Mini PEI sheet is “unavailable”. I want to get one on it’s way, since she was planning on using it in the class. I see a variety of sheets available on Amazon. I’d like to replace this with the same thing that comes stock on the Mini. Can anyone tell me the thickness of the stock Mini PEI sheet? Is there anything else I need to know when looking for a replacement?

Neither the teacher nor I know much about these printers. The problem is odd: On Dec 30 we printed the octopus test print with the sample of filament that came with the printer, then switched to PLA filament and printed out some test “S” plugs (basically 1" diameter X 1/8" thick disks with male and female “S” outline on them). Both printed flawlessly. The printer has not been used since, until today. Machine is still behaving oddly. We’ve got a call in to tech support. I’ll post more troubleshooting data in a new thread when I get more info. Just wanted to get the PEI on order for now.

John Mc

Not 100% sure on the stock thickness of the Mini sheets, but the TAZ can be made to work really well with a 1/8" thick sheet from mcmaster Carr and some 3m 465mp adhesive sheets.

You can also get them here: http://i-t-w.com/parts/pei-film-for-lulzbot-mini

Or whole replacement refurbished beds if necessary, etc.

edit: You’re also still under warranty and Lulzbot has a really great relationship with schools in general (lots of donated printers, etc.) call support up, explain the situation and they should just send you the parts.

Thanks, Piercet. I’m trying to keep this printer as close to stock as possible for now. Neither of us are very experienced with 3D printing. I figure the less we change, the more we are able to use the stock profiles and recommendations from other users.

Also, I’m sure being in a classroom setting, this isn’t the last time they’ll trash a print bed. Those 1/8" thick sheets are a bit pricey if it’s something they are going to go through from time to time.

Another question: I didn’t look too closely at the bed. I did see a hole melted through the PEI. Is it possible that more than just the PEI was damaged? What the next layer beneath the PEI?

I think you are wise to stay with the original thickness if you can.
Otherwise, you will probably have to change your Z offset, and maybe some other things.

It looks like my PEI is about 0.030" thick on my mini, but that’s just a guess. It is pretty thin.

It is glass underneath, so I doubt you wrecked that.

I’ve read the PLA causes issues with bed leveling. My thought is that the Cura leveling temperature for the nozzle might be too low. I’ve only recently changed my nozzle leveling temperature, so I can’t add any value here. Yet.

Good luck with it, and you are a good guy for donating to a school so the kids can learn the new technology. Thank you!

So I have some replacement .030" PEI from I-T-W.com (hopefully sitting in my mailbox as I write this). I found the workflow describing the Mini PEI replacement procedure. It shows applying the PEI “dry” onto the glass bed.

I could swear I read somewhere on here about someone praying down the glass bed with isopropyl alcohol or with Windex, then putting the PEI down while it the surface was wet (a procedure often used when putting screen protectors on smartphones or iPads). I can;t find that post now. Was I hallucinating? Is this a bad idea? If it doesn’t ruin the adhesive, it should make the PEI easier to get in position and get the bubbles out. However, the alcohol or Windex might prevent the adhesive from ever sticking. How are you folks normally doing this?

The Windex and soapy water works when replacing PET bed surfaces. I do not think that works with the adhesive used on PEI. Older TAZ printers shipped with green PET sheets on the bed. That is probably why you saw those tips floating around.

Thanks. I was thinking it might be an adhesive issue. The PEI vs PET thing didn’t even cross my mind. Glad I asked.

The B.O.M. shows .010" PEI.

You’re right. I just put a micrometer on my old sheet. It measures .011". I haven’t opened the new sheets I ordered, but they are “official” Lulzbot replacement parts, so I’m assuming they are the same thing as what came on it new. I’ll double check before I install them. I assume if they are a different thickness, I’ll have to adjust the Z-offset accordingly.

If the new one is thicker, it shouldn’t affect performance at all, but you might have to change the offset. PEI can be a bit thicker than we use generally before it starts being an insulator.

I don’t think you’ll have to adjust the Z-offset if the thickness is different. The auto-leveling metal discs sit on top of the PEI sheet, so they should move up if the sheet is thicker. Or am I missing something here?

I’m pretty sure Z offset is related to the distance difference between the discs on the corners and the surface of the PEI.

Possibly that relationship got disturbed a bit when I removed the bed and replaced it. Maybe I snugged the washers down a bit tighter, or a bit of crud from the manufacturing process was in there and got knocked off? Or maybe it was always a little low. We had only done two prints prior to having to remove the bed, and neither of those prints was anything critical (nor did we know what we were looking at at that point).

The computed Z height is not changed by the thickness of the PEI. It is based on the distance of the top of the washer to the surface of the plastic sheet. And since it is the same corner washers hopefully the distance does not change. I have seen washers that are tilted sometimes thought, so that is something to watch out for.

Understood. No obvious tilt to the washers, but when we’re talking tenths of a mm, maybe it’s not something I can eyeball all that well.

Question: the paperwork that came with the Lulzbot says the Z offset is 1.32mm (no negative sign). Is positive Z a downward movement of the toolhead? So if I want to move it up slightly, I need to change that to something like 1.25mm?

I’ll check the existing setting when I get to the printer this afternoon.

Z-Offset positive numbers move away from the bed, negative toward. It is calculated after bed leveling and other firmware adjustments are applied, so you don’t adjust it based on the firmware setting like that. Just note if you need to go up or down from where it starts printing the first layer and move small amounts at a time, I usually do 0.1mm increments. Sometimes dropping to 0.05mm if I really want to dial it in.