Bed levelling (and also print surface discussion).
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If it's machined flat, then in a new printer build it would save the cost of an aluminium tool plate for the bed, which makes it better value.
Good point. I have it on my todo list to replace the 10mm thick plate with something thinner - hmmm…........
Edit. ..........but then it is handy to have a removable surface such as glass, in order to rapidly print multiple parts without having to wait for the bed to cool.
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If it's machined flat, then in a new printer build it would save the cost of an aluminium tool plate for the bed, which makes it better value.
Good point. I have it on my todo list to replace the 10mm thick plate with something thinner - hmmm…........
Edit. ..........but then it is handy to have a removable surface such as glass, in order to rapidly print multiple parts without having to wait for the bed to cool.
I like that facility too. On a printer with a non-removable bed, I would want a fan below the bed to cool it faster when the print is finished.
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I got a good price for 3mm PEI sheet from a Chinese distributor. I haven't ordered it yet because I read that material thickness is hard to keep flat using adhesives. I originally though to mount it to the tool plate with stainless flat head screws but now I'm unsure, I'm afraid that method will produce bulging around the screw heads . Has anyone used a thick sheet of PEI? Thanks…
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I have never tried PEI that thick but I think it will be sub optimal for a number of reasons
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loads more PEI than you need. PEI is useful as an adhesion surface, other than that it is an insulator which does not help your heated bed.
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As you mentioned: difficult to keep flat. I have used thinner ~1mm PEI and an issue is the adhesive coming debonded over time. The 3mm will have the same problem but probably earlier as you will be pumping more heat into to maintain the same surface temp.
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PEI is pricy why pay for what you don't need.
Regarding screwing it down. You will probably get a air gap in the middle which will mess with the effectiveness of the heated bed. It won't be flat around the screw heads either
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I had thought to use a combination of adhesive and fasteners on the thicker sheet. I imagined the extra thickness would improve durability and flatness given the larger surface area of my bed. I had not given proper consideration to the insulator effect, do you think it would act more so than say a 6mm piece of glass? The price quote I got for a 560 x 803 x 3mm sheet of PEI was less than any of the print surface supplier here are charging for their thinner material….given equal size that none of them offer. Thanks...
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I've just renamed the title of his thread to reflect what is now being discussed (which is probably more useful than my initially shameless bragging).
Ian
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hey Simspeed
I found that the adhesive debonding was relatively random (ie it did not debond in the middle or the edges in any sort of constant way). The only exception to that was if I was impatient anf forced a part off a hot bed - that caused debonding in extremis. A thicker sheet of PEI should be better at resisting that sort of (user imparted) force. The other force you need to consider is the thermal expansion/retraction which is part of what the glues have to put up with. If you are going to screw it down then check to see if the difference between the expansion of the PEI vs what its screwed into is significant room temp vs bed operating temperature. As the bed size increases this become more of an issue.
For durability. It will obviously be more durable that kapton tape (really really thin) but after you get over a certain thickness I am not sure what benefit you get.
In general plastics are better thermal insulators than glass (which is not a great thermal insulator or conductor). Using Google I got the following properties:
Glass (ordinary) 0.8
PEI 0.22
both in W/m K so doubling the thickness between the glass than the PEI puts it in the same order of magnitude.But actually all of this is secondary to the flatness. If the PEI sheet is flat, and stays stuck down and flat then it will probably work well.
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Ian… sorry for hijacking your thread!
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I just want to chime in and say that using very thick PEI is, IMO, much superior to the thin stuff.
I use a 3.2 mm sheet on several printers, for almost two years now. Sometimes the thicker pieces do have a bow to them, but they can be held flat easily with a clamp or simply binder clips. The thicker sheet does not at all insulate the bed too much, in terms of heat. I use a 12v 280mm PCB heater, and it can get the bed to 120 no problem (other than being at the max rating of the PCB heater). The surface temp of the PEI is about 5 degrees lower than the reading at the PCB heater, with a 3mm mirror and a 1.27mm aluminium heat spreader sandwiched between it all.
The advantage of the thick sheet is that it does not need to be adhered to whatever makes the bed flat, it only needs to be clamped. Also, it can be sanded over and over again (when needed) to give extra print adhesion and to renew the surface texture on the surface.
The downside is cost – but consider the savings of not having to purchase adhesive to adhere a thin sheet of PEI, as well as never having to replace it (thin sheets become damaged much more easily) I think the thicker sheets are the way to go.
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Bot thanks, that really helpful - good point about the binder clips.
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I posted an earlier reply to you comment Bot….just disappeared?? I said I appreciated hearing from someone like you with a positive experience with the thicker PEI sheet. That's encouraging...I think I'll go ahead and take a chance on a sheet for my build. Thanks....TP.
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I'm wondering what PrintBite actually is. I'd sort of assumed that it was PEI stuck to something. It has a very fine texture to it - like very finely etched parallel lines. so maybe it isn't. Whatever it is, my measurements tell me that there is 13 deg C temperature difference between the top surface and the bed, whereas with plain glass the temperature difference is around 2 deg C so from that I deduced that the PrintBite was insulating by 11 deg C. So in theory, if I run the bed at 70 deg C instead of 50, it should work (for PLA). I wonder if I just got unlucky and it's a bad batch? I got mine on 8th November 2016 and it was the first a new batch. Did anyone buy any at around that time or after, and if so, does it work?
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I got a tiny piece for my micro delta just 100mm diameter, probably around early December which is the best piece I've had so far, abs stays bonded down to 56 deg C. My large sheet on the kossel Xl releases abs at about 85 deg C.
As for what it's made of it has a sort of fibreglass like texture and weave. But I don't know what it's made from.
You do need to be achieving 60 on top of the printbite for pla and 110 for abs which I find is 70 or 120 set temp.
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The stuff I have is an early one that came without any backing adhesive or grid marking's on it?
Mine is attached directly to my Ecocast plate and just works.
@simspeed do you have a link to that Chinese PEI Supplier please?
Doug
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PrintBite seems to be a type of G-10/FR-4 sheet, allegedly with a treatment done to it. I think it is simply an off-the-shelf G-10 sheet with branding applied and price marked up.
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Well I don't know I'm sure. I dug out my piece of glass with PrintBite on it. Gave it a clean with soapy water as recommended. Heated the bed to 85 deg C, checked the temperature on the surface and it was at 71 as measured with a thermocouple stuck on with 3 layers of Kapton tape. Tried printing something with PLA - nothing - zilch - nada - might as well have been trying to print ice. All I've got is another birds nest. SO I wacked the hot end up from 195 to 225 (no print cooling fan). Cleaned the PrintBite again - this time with Acetone. Dropped Z homing by another 0.1mm. Tried again. The only difference was that this time it was a wider, flatter string of filament that didn't stick. For whatever reason, this stuff just isn't going to work for me.
However, one useful thing has come out of this exercise. I've found how to remove it from the glass is you need to. You just need to pry up a corner with a strong flat blade being careful not to bend it too far (I used a gasket scraper). Once you have a little gap, pour Acetone into it - this dissolves the adhesive. Continue widening the gap and pouring in more Acetone and voila! I now have another piece of glass that I can use for testing something else (or at least I will have when I get the rest of the adhesive off).
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@simspeed do you have a link to that Chinese PEI Supplier please?Doug
Hi Doug….here is the link. Address your comments to Cun Zhang and mention me (Terry Peterson) if you don't mind. They quoted me $106 for a 560mm X 773 x 3mm sheet of PEI 1000. I am revising the size to 803mm long for repricing so I'm sure it will be a little more. I plan to place my order when the repricing hits my inbox. Best of luck...
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Nice price on a piece that size. I've never tried a piece larger than a 280 mm octagon (measured from edge to edge) with just clamping, so if the piece comes with a natural bow you may have to fasten/adhere it in some fashion.
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@ Simspeed
Thanks for the Link now what is interesting is that they start at 1mm thick and go up to 100mm but they also do it in Black now don't know if that will impact on how it performs as a print surface or not?
also std size of 500x500 is interesting and even 1000x1000.I will drop an enquiry in a little later and see what comes back?
Doug
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The black one would probably be ideal to use with the IR sensor.
