Alternatives for the printing bed?

Hey folks,

I generally love the LulzBot mini and the excellent support, but I’m having issues with the printer bed.

In 3 months, I am now on my fourth heated bed. All through this I’ve been cleaning the surface with isopropyl alcohol, and trying to follow instructions as well as I can.

  1. The first one, I was trying to remove the print and the PEI sheet tore.
  2. I replaced the PEI sheet. It takes about 2 hours of tedious, delicate work to remove the adhesive and re-apply the PEI.
  3. I ordered a new heated bed kit as a backup. The first one I received was smashed. Lulzbot fortunately replaced it.
  4. The original bed that I had replaced the PEI, I was trying to remove a print, and the entire bed shattered.
  5. I then switch to the backup bed. While printing nylon, I saw some warping on the bed that I assumed was the nylon itself. It turns out that because of a bed leveling issue (apparently sometimes it doesn’t detect the height correctly), the hotend was too close to the PEI and the PEI blistered.

I’m a little bit at wit’s end. Is this other people’s experience? Do folks have alternatives/modifications to the standard LulzBot mini bed that they’ve made that maintain the nice characteristics (like auto-leveling)?

If you managed to tear a PEI sheet removing a print, you are doing something wrong in your removal process. To remove a print from PEI you are generally supposed to let it cool to 60c, (not all the way cold) and then use a thin flat tool to gently separate the print from the bed starting at the edges. A paint scraper or a cheese slicer with the slicy bits taped over works well for this. Ripping a PEI sheet is not normal. Shattering a bed is not normal. How are you removing the parts currently? what tools, what method, what temperatures?

You could switch to an aluminum plate bed with a buildtak surface, but that may not help if you are removing the parts improperly, you’ll just blister the buildtak.

I was using a razor tool that others have recommended for removing things from the bed (http://www.thingiverse.com/thing:34481) when the PEI was damaged.

When I shattered the build plate I was using the Greban that came with my Lulzbot Mini. I sometimes am not there when prints finish, but then I heat it up to the temperatures recommended in the lulzbot profiles page (https://www.lulzbot.com/mini-cura-profiles).

I wouldn’t use a razor… When you slide the edge under the part, there’s a good chance you’re slicing into the PEI. Get something flat and blunt or a icing spatula. The TAZ tool kit has a clam knife which has an edge, but is for the most part blunt.

Get the tool under the part, and lightly tap the handle to move the tool further under the part… prying it off. Try not to use the tool as a lever to pry too early in the removal, it could gouge into the PEI also. Use a fulcrum and push down on the tool handle.


EDIT: Are your prints more difficult to remove than before? The difference is probably the bed leveling. Clean the contact points, nozzle and change the wiper. If the discs or nozzle is dirty (could be a thin layer of filament residue), the bed-leveling process won’t work properly. It will press down on the discs, causing the initial nozzle height to be to low… which will cause the print to stick too well to the PEI.

The school I gave a Mini to had the tool head take a nose-dive into the bed on their first print attempt. Fro looking at the damage, it was evident that the left rear washer did not make good electrical contact with the nozzle during the auto-level sequence. So that corner got pushed further down, until the nozzle forced its way though what ever was preventing contact. This resulted in the controller “thinking” that the bed was sitting lower than it actually was. PEI sheet gouged in a couple of places, and a nice big hole melted through it. From reports here, PLA filament is

No problems since replacing the PEI - I’ve trained the class to watch to make sure the bed isn’t moving during the auto-level sequence, and abort if they see a movement. I’ve also noted that if you watch the endstops report during autolevel, you can tell if one of them is out of line with what is “normal” for that printer. Someone has written new firmware and posted it on here; it can automatically detect those problems. Let me know if you can’t find it, and I’ll try to dig up the link.

The class also had problems with the prints sticking too hard. Fine tuning the e steps calibration and putting in an accurate value for filament diameter helped some of that problem. After doing that, I also adjusted the Z offset to raise the print head up a bit. It was only a small adjustment: 0.1mm, but it made a significant difference. Now the parts are removing much more easily, and the surface quality of the first layer is much improved (I think the nozzle was dragging through the extruded filament too much).

I just had my PEI tear, so I’m curious about alternatives now. I had some blistering, I suspect due to running it pretty hot, at the upper limit. It tore along one of those. I consider it mistreated and my own fault. I know some of the TAZ users have converted to an aluminum plate with the heater on the back and something on top. Has anyone considered something like that for the mini? Maybe with something like buildtak or zebra? A removable plate with some flexibility sounds like a good idea for easy part removal and if you had 2, quick swaps. The auto leveling washers would need to be made quick to release for something like that, but it’s likely not too hard to do something like that.

I may well end up with another PEI. Just curious about what the options are.

Removable plates like PrintinZ Zebra and Fleks3D. Or stick on plates/films like Buildtak are good alternatives.

Its hard to mill Aluminum to a completely level surface. The surface grades can affect cost of the bed. Glass is much more uniform / level surface. Aluminum seems to be a better/faster conductor of heat.

I hadn’t heard of the Fleks3D, I like the look of it from their website, so now I have a new research project. The ability to pull the whole thing off and just bend it a bit to release would be great, if it’s reliable, flat, and holds well while printing on it.

Good point on the Aluminum plate. I know at least one TAZ user got a plate that was out of spec. Glass is amazingly consistent with that sort of thing. It’s also pretty cheap and easy to get more. Interesting thought about heat transfer, I wonder if anyone has tried copper. Probably difficult to keep flat, it’s pretty flexible.

Not that I don’t like the PEI, it works well. But if I have to replace it anyway, might as well check out the options.

I read somewhere about someone experimenting with the tempered glass screen protector material that people often put on iPhones, iPads, etc. (This is the glass stuff, not the plastic sheets.) They seeme to think it was working well, but had not used it very long as of the time of that writing. They came up with the idea because some of the more exotic filaments were sticking too well to their bare borosilicate glass bed and taking chunks out of it when they tried to remove the prints

Interesting idea with the tempered glass screen protectors. Reasonably cheap, easy to replace.

I contacted the Printinz guy and am going to try a Zebra plate. I suspect I might need to adjust the firmware auto-leveling code a bit to get a bit more Z clearance for the travel moves and calculate the zero point. I can manage that. I should get the plate next week, so I’ll report back with a little review and updated code for the firmware.

The code changes won’t be needed if one were to put it under the leveling washers. I wanted to try having it removable though, and clipped down, so the washers will be at the stock location with the corners of the plate trimmed off. There are some reports of height tolerance being a bit rough, and the spec is +/-0.4mm… That’s pretty big, but people print on them without too much issue, so I’ll give it a go.

Fleks3D looks interesting, but isn’t shipping yet, so I’ll consider checking them out later. And I’ll probably order some PEI and tape from Amazon to fix the stock setup as well. For now, I can just use the non-damaged part of the bed, as I rarely print large enough items that it’s an issue. I also read some reports of people clamping slightly thicker PEI sheets down and using it as a removable plate. That could be an interesting alternative as well.

Maybe I should make those code changes configurable… :smiley:

Add spacers to the washers so they “seem” to sit on top of the Zebra plate.

Oh fine, make it way too easy… :smiley:

I was tossing around something like that. Maybe print up a basic spacer and use a longer screw on the washer. Guess I should look up the BOM and figure out what the size is. I’ll likely have to order some, can’t find Metric around here. :unamused:

In my experience, letting the bed cool all the way down to room temperature helps with removing most materials from the PEI. What materials in particular were you using when you damaged the print bed?

I was printing PETG. With HIPS, I found that cooling usually released the prints by itself, no help needed. PETG usually loosens up some that way, as most materials do. However, Lulzbot has said they don’t recommend letting the bed cool all the way to prevent damage. So I’ve been holding temp at levels based on a chart from the Taz 5 instructions. The manual my Mini came with didn’t include removal temps. In this case, it was 45C.

Another thing to note, the damage to the PEI was a two part affair. This tore a bubble off. The bubble got there after printing Nylon at a higher bed temp, 110C, I think. It was under the part after cooling and removing it. I can’t say what happened there, I can only guess the higher bed temp combined with pressure from the shrinking Nylon caused it. I suspect the bubble caused the PETG to stick tighter, being a bit closer to the nozzle. That made it harder to remove the part, in the process breaking the PEI.

I figure this is one of those things that happens with printers and is partly my fault. And if I’m going to replace it anyway, might as well try a couple alternatives as well. If I can get a removable setup reliably working, I have considered stripping the glass bed down to bare glass, then using clamp on surfaces or other treatments like glue stick that work best for the material I am using. And if I don’t like the removable setups, I can always get some PEI and double sided tape to set it up the way it was.

I agree with Piercet, however, just FYI, Lulzbot now recommends 50C and from my testing it seems to work better. It seems like the adhesive is still gummy at 60C and it tends to create bubbles.

I didn’t read through the whole thread so it may have been stated already, but changing the Z offset or reducing the first layer thickness did the trick for me.

Is anyone using zebra plate on a mini? If so, how did you deal with the self calibration process and how did you attach the zebra plate to the bed?

Here’s an alternative that is kinda low cost and works a LOT better then the approaches mentioned so far.
Go get some plane old plate glass cut to size at your nearby HW store(emery cloth the edges). Then guy buy a can of Aquanet super extra hold unscented hair spray. Not ANY HS!!!.. ONLY Aquanet super extra hold. Two base coats then a light spray before you print. Adjust bed height for a good initial squish. Total cost is about $5. The AQ can will last a lot longer then the super expensive alternatives yet it is a heckalot more capable with stick AND release. Actually you can get a couple of plates so that while one is in the freezer releasing a big print you can use another.

I have not used Zebra plate. If by “deal with the self calibration process” you mean how do you adjust the Z-offset to get the right starting height, there are several threads on here with information about storing a new z-offset in the firmware (here’s one of them).

You can also fine tune the z-offset from within Cura under the Machine menu, choose “Machine Settings”. By default, the number here is zero, which means just use the number stored in firmware. If you enter a number here, it takes the number stored in firmware, adds your entry, and uses the result for initial z height. A negative number moves the head downward, a positive one moves it up. So for example, my Mini came with the Z-offset set to -1.33. If I enter 0.1 in the z-offset box, I get -1.33+0.1 = -1.22mm for my z-offset (I’ve raised my z offset by 0.1mm).

Personally, I prefer to store the number in firmware, so th enumber is used no matter what computer I’m tethered to, or what software I am using to control the printer. However, the Cura menu selection is a handy way to make a quick change.

Are they planning on updating their end g-codes in Cura to address this change? Or maybe they have, and I missed it. I’m using Cura 19.12 and the default start and end g-codes that came with it.

I am. You have 2 options here. You can get one cut to the glass dimensions and use longer screws or standoffs to put the washers on top of it. The auto level works fine this way. It might be more prone to warping though, and is harder to remove.

The other option, that I used, is to ask them to cut the corners off for you. Tell them it’s for a mini, they know what to do. There’s a link below, it includes some pics and other info from my setup. This method is nice as it allows you to remove the plate by pulling a few clips off. The auto level works fine, but you need to dial in the Z-offset a little more. For it to work with the leveling program, I used some metal PCB standoffs I had around to push the washers up above the zebra. It almost worked without that, but the part cooling duct bumped into the plate. The standoff threads are M3, about 5mm tall.

http://www.printinz.com/lulzbot/