Corners Lifting Big Prints

I wondered if someone could help me with corners on my Bambu A1 when printing large prints. I have attached the 3MF file. I have also attached a photo of what happens.

The corners seem to have come away and it is not flat. I am printing a couple of these for family gifts for children but my step mother in law (I unfortunately have two mother in laws), when I showed them my version, mentioned something about the corners. I was tempted to tell them to shove it up their backside for me printing it for their other grandchild.

But also, I would like to solve this problem as I have had it on another print I did recently.

What I have tried;

Bunny ears, the largest I could do and 3 stacked around each corner
A brim of 0.5cm and 1cm with a 0.1cm gap
I have increased the bed temp from 65 to 70 and then 75
I have turned off the cooling fan - even though it seemed to be still spinning
I have tried different filaments - Bambu basic black, bambu matte black, bambu matte grey
I have printed it on the BL textured plate, I have printed it on the BL smooth plate, I have tried the other print I am having issues with on an aliexpress plate.

I just keep getting the same issues. The bunny ears reduced it dramatically but I just can’t get it to behave and give me a flat print in all 4 corners.

I have read other posts but can’t seem to find a consistent solution. I am close to buying a X1C or HD2S in the Black Friday sale thinking this will solve it with them being enclosed, but if I can get it sorted on my A1 it will help me learn.

Does anyone have any other ideas please?

Safe_V3.3mf (4.2 MB)

You haven’t said what plastic you’re using. If it’s not PLA, you’re not going to have good luck since the warping happens because the print is cooling off too fast while it’s printing. You need a printer with an enclosed build space like the X1C.

Warping can happen with PLA, too. Especially when the ambient temp is lower.

To test if an enclosure will help, get a big cardboard box and put it over the printer before running your print. It may not make it perfect, because the interior isn’t going to heat very much, but if this is your issue it will improve the print.