Welcome to the SeeMeCNC Community

So I love BuildTak (I would probably love PEI, too, but thus far have only used BuildTak).

What I don't like when using BuildTak is that the glass is quite a smooth surface to adhere to, so sometimes the bond isn't the best.

Another thing I don't like is that the prints are hard to remove sometimes, and I end up damaging the print or the build surface when removing it.

After thinking about the Tiko flexible build plate, and the "Printinz" flexible build plate (fiberglass), I decided to head down to my local plastics dealer and pick up a piece of scrap Lexan for $5.
As you can see, I've been using an onctagonal mirror for a build plate after smashing my borosilicate (thanks to the BuildTak ). I used the mirror as a template, and also have the mirror sandwhiched upside down between the heated PCB and the polycarbonate, so I have something flat to clamp it to. The poly was already basically perfectly flat anyway, but this helps make sure it will stay as flat as it is.

The 1/4" polycarbonate isn't THAT flexible, but it will not break, so with enough force pressed against a leg, there is enough flex to get even small parts to "pop" their corners off the surface, so you can get a spatula underneath without damaging anything.

A step that I forgot to take photos of was that I added an eight-way crosshatch pattern of scoring to the surface of the plate with some 600 grit sandpaper, to give the BuildTak glue something more to bite into. I'm certainly pleased with my $5 experiment.

I ordered 5 sheets of BuildTak few days ago, I still didn't try it.

It's a good idea you had there, and I will certainly give it a try.

Won't your plexiglass warp when heated ? How can you ensure it is absolutely flat ?
As a Buildtak user, how often do you replace the sheet ? Does it get damaged when the nozzle is too low ?

This is not plexiglass, but "Lexan." Plexiglass is acrylic, I would advise NOT using plexiglass/acrylic for this. It must be lexan/polycarbonate.

Polycarbonate has a high glass transition temperature, and is dimensionally stable up to about 110 degrees celsius. I only ever print at 105 the most, so I should be good. I tested this before applying the sheet. I heated the bed to 50, let it cool, then 75, let it cool, then 100, and it was always the same flatness. I used a straight edge to determine this, but also used the reflection from the shiny surface to gauge this. The very edges of the sheet were slightly distorted, perhaps by the clips, or perhaps from stresses caused by me sawing the sheet, but the print region is as flat as I can determine.

The BuildTak is EASILY damaged by having the nozzle too low. I suggest you ensure your print plane is level before installing the BuildTak. I replace the sheet after a few weeks. The first few sheets should be considered disposable tests. I went through about 4 sheets in the first week, getting the hang of it, and then the next two lasted two weeks each (of very heavy/abusive printing).

If I had used the polycarbonate bed right away, I probably could have made many of the sheets last longer. Removing the piece is when almost all the damage occurs, if your nozzle doesn't smash into it first.

One thing to be careful of is to install the sheet VERY SLOWLY. The first time I followed the instructions but went too fast, and had bubbles underneath from the get go. Going slow and careful prevents this.

Thanks for the advice.

I still did not receive my order... but anyway my printer is not functional right now.
I had to move it to the garage, to leave my office room for making a bedroom for my coming son.

I hope I wont ruin 4 sheets in the first week, as it would probably mean me to give up on the product, as I can't afford spending that much. Until now, I print on white paper. That is cheap, and it works well... just that it is messy when you scrap the paper off...

I always print right on the glass with either hairspray or gluestick, and it's always worked well, but now I'm wondering about just using a sheet of polycarbonate with hairspray...why not right?

I tried the hairspray on the polycarbonate, and it kind of worked, but the adhesion seemed a bit less than on glass. My next experiment will be bonding PEI to the polycarbonate...