I found one magnetic spring steel plate with PEI which fits exactly on the heated bed plate. It comes with a flexible mangetic sheet which has 3M adhesive on the bottom and can be directly put on the heated bed (just cut of the corners to make space for the screws). I've not tested yet how well it works (maybe tomorrow) but I got it from here: https://www.aliexpress.com/item/33032347795.html
Yes, it works well. It also heats up way faster than my previous thick aluminium plate. The only thing bad is the border is not deburred.
I like the idea, but I'd want the wole lot to be removable. Perhaps if the lower (magnetic) layer were stuck to a spring steel sheet that had a small amount of bow; to pre-tension it effectively and press it down to the heated bed when held by clips at the edges... I bought three of the E3D borosillicate beds and a sheet of polycarbonate. One sheet of glass has PEI stuck on with 3m, and two are plain glass. I've had reall really good results from printing nylon on PVA on one glass sheet and I'm really really impressed with Magigoo PC for printing polymaker PC-Max PC (90% polycarbonate, 10% 'filler' (styrene??)). Printing the polymaker polycarbonate is the reason I'd want the magnetic plate removable: I often have the bed temp set to 120 (to get a surface temp of 105 degrees). My printer is enclosed in an insulated cabinet (electronics chamber is open to prevent overheating of steppers/electronics). I suspect I'd easily get past the curie temperature of the magnets so it'd have to be removable. I also print the occasional small part onto adhesive covered glass in natural polycarbonate and use temps of 150 for the bed. The polycarbonate sheet was very cheap. I put some 120 grit on my random orbital sander and velvetted the surface (high speed). This is actually REALLY good (a little too good, perhaps a release agent like window cleaner.. needs more experimentation) and you can flex parts off it. I got 4mm which is a little thick for this, perhaps 3mm is perfect.
Why not just keep the magnetic base attached permanently and then just put the PC sheet on that if you need it. It's just one mm thick and you could also use magnets to hold down the PC sheet. Or you could buy PC film and glue it to a spring steel plate.
Because I would be VERY surprised if the magnets in the sheet have a curie temperature of 150 degrees C! - This is the temperature that the magnets will loose their magnetism, permanently.
Ah, indeed. I overlooked the 150C, the magnet base is only good for 140C, accounting for oscillations probably less.
I'm actually very surprised its that high! Not bad! Wonder how long it'll last at that temp? I thought it would be more in the order of 80 degress.
It's probably because the magnetic base is a flexible magnet which is usually Ferrite in some kind of rubber. The Ferrite usually has a high enough curie temperature, but the rubber binder degrades at some point.
I wanted to stick everything (magnetic film) to a borosilicate glass bed but I don't have a good way of clamping that to the heated bed without the clamps getting in the way, anybody have any ideas for that? I was looking at the Clever3D milled aluminium beds with the recessed edges and thinking of placing some powerful magnets either embedded in that (will have to make my own pockets) or just stck them underneath the whole stack.
It is janky, but I used Kapton tape along all 4 sides of the glass bed and it has stayed surprisingly secure.
My solution on a printer that I designed is to make the bed plate and glass 15mm larger than the printable area at the edges, to leave room for bed clips.
A late addition to this thread - the AliExpress seller linked by the OP is now showing photos of some chunky magnets placed under the original heat plate (without milled pockets), so that the steel sheet can be held down without using the rubbery magnetic sheet. See here. They are selling "3x14x24mm N52+" magnets for this purpose, allegedly good for continuous use at 130c.
