I take advantage of google translator services to better express what I want to say.
I've been battling for a long time with print surfaces. From an MK2 base of aluminum with lacquer, borosolate glass with or without lacquer, abs glue or stick.
The first attempt to make a removable base was with a sheet of ferritic steel attached to the base with a series of magnets. On that sheet, not very flexible but enough to remove the pieces, I put an original buildtak sheet. He did not convince me, although at that time it was the best option I tried.
It lasted little and the price, for a non-professional use, was excessive. I started testing Aliexpress printing surfaces. The only advantage was the price. But any error of first layer that lowered the head caused that the sheet was broken when retiring (or to try) the piece.
It must be said that I use DC42 IR Probe to adjust the two Z motors and to level the print surface (G32 and G29). That is why there were errors in the first layers depending on the material / color of the print surface.
Reading David's instructions at miscsolutions I tried to test the PEI sheet that has received such good reviews everywhere. So I bought a kit from Aliexpres and a sheet of magnet from Amazon.
The first thing I tried was the PEI directly on the flexible surface of steel. Too much reflection The IR sensor gave too irregular surfaces and each first layer had to be adjusted by Z Babystepping.
I leave the image to see how the IR sensor detected the surface as it arrives from the vendor.
The result was not very good and I tried to paint the metal surface before sticking the PEI sheet. I gave two "layers" of paint with a permanent marker then I attached the PEI sheet on top. Unlike other sheets, the ones I have used are very fine, in the order of 0.125mm. and they are not manipulable as mentioned in the Miscsolutions website that I have indicated before. The result was not encouraging, on the contrary. The permanent marker was excessively bright and the IR sensor detected the surface in a more erratic way as can be seen in the next image.
Finally I bought the paint spray-on barbecue & stove paint recommended on the Miscsoutions website and all the problems were finished. I gave two layers of paint with two separations between them. I cured them in the oven at 170 ° C for two hours, I stuck the PEI sheet and the result is in sight.
It must be said that between the tests, there has been no correction of the height in Z. My printer is a Hypercube Evolution with a micro switch on Z- and the IR sensor to level the surface and that all the tests I did same day, since I have several sheets of flexible steel and I have been able to mount the three configurations to see the differences.
Regarding printing features, I have found that PETG does not need any adjustment. First layer at 15-20mm/s, bed temperature between 50-70 ° C and filament at the temperature marked by the manufacturer.
ABS I have not tried it yet, until it gets hotter and can have the ventilated house I will not print with ABS.
As for PLA and other compounds of PLA (Glow in the Dark), I must say that I raise de bed temperature of the first layer between 75-80ºC so that the first layer adheres well. In first complicated layers, which have many profiles, shapes, hard angles and holes, it helps a lot of lacquer, but lowering the speed does not need lacquer.
I usually print at 0.15mm layer height with a first layer of 0.2mm
The best of this system is that you can remove the print surface outside the base and remove the piece by flicking the steel sheet with PEI.
I first tried with high temperature magnets, which needed a base machining to be able to reliably put them. Then I went to the magnetic sheet and, for now, holds 115 ° C without losing magnetism.
Sorry for the extension of the answer and for any mistake that that has passed the google translator reef, but I think it's good to share what has cost me time and money to get.
For days I have printed without any problem in the first layer and removing the pieces by simple bending of the base. Great!!