Either way, make me one for a Mini, OK? 
No offense but a vacuum just sounds like over engineering.
Magnets would be a better option and are currently being used by the Geckotek plates. I believe they use ceramic Magnets to hold up to the heat.
Iāve currently reached out to some local plastic manufacturers around me regarding a thicker PEI sheet that isnāt bowed and has correct tolerances. Iām waiting to hear back from them. In the mean time I see McMaster Car is also selling PEI and they are claiming +/- 0.003" thickness tolerance on their 1/4" thick sheets. (and +/- 0.0125 on their 1/8" sheet (not nearly as good)).
If their tolerances hold true and the sheets are not warped. This seems like a viable and the best option to me. McMaster is know for higher quality.
I figure a thick enough PEI sheet wonāt raise up in the middle of the bed, even if the print pulls on it.
Having ordered a thick ~1/4in sheet of PEI, like most plastics, it warps badly after exposure to moderate ~65C temperatures. Supposedly though, fiberglass reinforced PEI was originally chosen by the reprap project, prior to bonding thin plastic sheets to glass. High cost eliminated the material at the time. Only link I can find to this now is here - https://groups.google.com/forum/#!topic/deltabot/17FN_Zpb6v0 .
Resin casting is extremely interesting though, because it raises the possibility of using additives. We could try making fiberglass, carbon-fiber, or even kevlar reinforced PEI. Another possibility might be to include ferromagnetic particles, allowing the entire bed stack to be clamped with strong magnets.
Interesting, this stuff is supposed to be heat resistant and itās glass transition is way higher than anything it gets close to. Iām shocked to hear it warps.
So basically the community started with Ultum 2300 (30 percent fiber glass infill) and got cheap and moved to. Small layers on glass.
Am I seriously the only one dealing with bubbling? A typical build plate is $50. And they all tend to have weak points. Iād gladly spend $100 on a far superior build plate.
I take it you havenāt seen the rest of my Taz then?
Ultum 2300? Where can a sheet of this be bought, and at what price? If this stuff proves rigid in testing, then it would definitely support the case for further research with custom resin mixtures.
Also, keep in mind that 3D printers have tight tolerance requirements. When I say ābadly warpedā in this case, I am talking about 4-5x 0.35mm nozzle first layer heights. FWIW, IIRC a roughly 150mm * 150mm square in the middle of my 300mm * 300mm sheet of thick PEI seemed to remain usable.
Itās Ultem 2300 PEI. Basically this stuff
https://www.sabic-ip.com/gepapp/eng/weather/weatherhtml?sltRegionList=1002002001&sltPrd=1002003064&sltGrd=1002012722&sltUnit=0&sltModule=DATASHEETS&sltVersion=Internet&sltType=Online
You can buy sheets of it here for $450, which is about the best price I have seen https://www.onlinemetals.com/merchant.cfm?pid=15464&step=4&showunits=inches&id=1139&top_cat=0
Or a remnant sheet for $130
http://www.ebay.com/itm/25-x-16-x-16-Natural-Ultem-2300-Sheet-Plastic-30-Glass-Fill-PEI-/251615771158?hash=item3a9577fa16:g:-1EAAOSwDk5T6lvQ
There are also all sorts of other percentage of glass fill resin types out there for PEI sheets, some of which may be cheaper because no one is looking for them.
https://www.sabic-ip.com/gepapp/Plastics/servlet/ProductsAndServices/Product/series?sltPrdline=ULTEM&sltPolymer=PEI&search=Search#searchresults
Thanks!
Paying $450 for a new sheet sounds ridiculously expensive though. No wonder this stuff hasnāt been used much in production!
I may try this, I really like this idea. Im going to add a dovetail cutter to my next mcmaster carr order.
I think if the sheet is slid in with the cup facing up it would cancel out.
For anyone wondering. I asked McMaster what their vendors tolerances on flatness were for their PEI/ultem sheets.
āI spoke to the manufacturer of the Ultem sheet and while the material is very flat, because it is cut from larger pieces a tolerance for flatness is not available. The larger piece they are cut from is within a tolerance of 1/8ā over 4ā length."
Nothing we didnāt already know, but I like knowing the hard numbers.
And Piercetā¦ Iāve seen your printer, its spectacular. Iām currently adding your Z-wobble nut to mine since my Z-wobble has recently been getting significantly worse (zero wobble out of the box, but 1000 hours of printing laterā¦). And I plan to soon after add the open rail modifications. All awesome mods that I do NOT consider āover-engineeringā. Sophisticated does not necessarily mean its over engineered if its necessary. I just question if a vacuum on a print bed is necessary! haha. Maybe it is, just sounded like there might be a more simple solution. You probably hear it all the time, but thanks for the mods and support you give to this community!
No, my PEI has bubbles all over and the glass itself is bowed (.1mm sag in the very middle which gets as low as .18mm on the left hand side of the bed). I now print everything at the front of the bed which is the only properly flat and unbubbled section I have. Luckily everything Iāve been working on the last few months has been pretty small.
Itās something Iāve been meaning to contact Lulzbot about for months but I guess itās not something thatās covered by warranty? The bubbling in particular which was probably caused by me.
The bubbling is covered by warranty. They will get you taken care of.
Iāve already had mine really replaced. I could probably do it again but to what point? Iām looking for a better more permanent solution and Iām willing to pay for it.
Itās a choice.
Itās covered the first and second timeā¦ possibly a third, but eventually they cut you off. 
Citing normal wear. I guess they figure you should have learned after the second time to take care of the PEIā¦ Or you shouldnāt be going through that many beds in a year.
You can add a sheet of PEI to this bed using typical 3m tape that Lulzbot uses:
Necro posting my own thread.
I have been contacting vendors. The best I have been able to find is Ultem 2300 12"x12"x0.25" for $109. The price is fine with me, however I have found that nothing will come close to the flatness required. Which means that a method to flatten it during print/use is required. I hate the idea of adhesive as so many of us deal with bubbling.
So now I acknowledge and agree with what everyone else and Piercet have been saying (I should learn not to question the guy).
Iāve been brain storming magnetsā¦ But this would require attaching them to the bottom of the PEI sheet which would defeat the purpose of avoiding adhesive.
Iām now starting to believe that Piercets vacuum idea is the best route. I am eating my words, lol.
Time to find someone with a CNC machine to create channels in an aluminum plate for me. 1/4" PEI probably wouldnt be necessary at this point, something lik e1/8" would be more than enough.
How about two sheets of 2-3mm PEI back to back? Bow side being the ābackāā¦
At that point wouldnāt it just be better to do a 3mm sheet on glass? 2 sheets back to back would still require adhesive and if they are both bowed opposite of each other, youād be dealing with twice as much internal static stress compared to 1 sheet on glass.
I guess my objective is 2 fold. A removable bed would be nice. But more importantly I want to get rid of adhesive so as to eliminate issues with bubbling (all while maintaining a flat build surface).
My PEI bubbles and pulls off the glass during a print. The ABS prints create enough tension that it literally will lift the PEI. The prints turn out great, the stick factor is great, but my PEI bed canāt handle the stresses. The weak link isnāt the stick between the PEI and the ABS but instead is in between the PEI and the glass. I donāt believe all bubbling issues are caused by user errors. I follow proper part removal instructions. But as I said, I notice the prints doing it mid print before I ever get a chance to damage the PEI by removing the part. I think itās just an inherent design flaw.
Im still under warranty and could maybe get another replacement. But at this point I feel like itās just sticking a bandaid on the issue.
With that said. A thicker piece of PEI taped/glued onto the glass may be enough to resolve the issues with bubbling. Maybe itās as simple as a thicker piece wonāt flex as much and thus wonāt pull up from the glass during printing.
I kind of liked the idea of laminating PEI resin directly onto an aluminum plate.
As for magnets having adhesive too, true, but you could just pull it off and replace it easily. I suspect it would be unlikely to have more than one let go at a time, so it shouldnāt effect the in-progress print much. I do like the vacuum idea though, itās a bit over-engineered, but thatās what we do around here, isnāt it? I know, do both!
Wellā¦ my understanding is that thicker sheets of PEI bow when heated. So if you can ācancelā out the bowing, then the PEI can be clipped to the glass bed with out adhesive.
I was originally thinking about epoxying the PEI to a CF sheet. But the CF would reduce the effectiveness of the silicone heater.
The bubbling I think is inevitableā¦ LB is starting to admit that as well. I went through 3 beds before my warranty. The third, they didnāt want to replace citing normal wear. I tried different removable plates, but ended up going back to PEI. Currently trying a little thicker PEI sheet with 3M 467MP adhesive. Iām hoping the thinner adhesive will be easier to remove when it bubbles. Overall its holding up pretty well.
Exactly my point kcchen. Iāve gone through 2 sheets and agree that the bubbling is inevitable. Iāve also tried other build plates and none of them are as good as the PEI.
Iām looking for the ultimate solution. Iām currently looking into getting a Vaccuum plate similar to what piercet described machined. Itās between the vacuum and Magnets. But honestly I think the Magnets would be a more expensive and less versatile route.
Looking through McMaster, Iām finding 303 aluminum plates with a thickness of 3-4 mm. They seem to be the most reasonably priced option. . Iām not overly familiar with aluminum. Will a sheet this thick flex? Obviously we wouldnāt be wanting flex.