This worked for me, have no idea if it will work for anyone else. For all I know it might break your build plate in half or do something equally awful. I had to fix a jam during this process because my warpage was so amazingly great that it wrapped about a foot of filament all around the inside of my extruder. You have been warned!

My acrylic build plate had warped over the years. So I tried standing on it to straiten it out and snapped it in half. With the makerware software I could make a good print using a raft. But when I switched to cura on octopi the raft was stuck hard to the prints. I tried putting packing tape down on top of the raft and that did work.

Then I had a thought. Why not print a raft just once covering the entire build plate, permanently attached to the surface of my broken build plate? Then I could print anything and it would come right off. And it worked!

Just clean your build plate and level it as well as you can. Then print the thin8.stl onto the plate with no raft. If your warpage is really bad you might want to try printing a few smaller shapes in the center or around the outside edge depending on your warpage to get the plate in the ballpark so that this will even work. Try to get it to stick as well as you can because ideally it will be the level surface you print on here on out. The first few layers might not evenly cover, because of build plate warpage. And I had to clear out a filament jam in the extruder motor section because of how much my plate was warped up on each corner.

Once the build of the new surface was complete, I covered the surface with packing tape, overlapping it slightly. I put glue stick down on this, lightly, mixed it with a few drops of water and made sure it covered the area where I am going to print. You also have to move the bed down a bit because this new surface is higher than the old surface, by loosening the thumb screws under the bed, and then just move the head around and use the thumb screws and your eyeball to get the tip of the nozzle just to the surface of the bed. Turning the thumb screws left lowers the bed, turning right raises the bed.

I print with a couple of brims and manually adjust the thumb screws as the brim is being laid down making sure that the filament is flat, not round, but not too flat. The brim should be even clear around the print.

My prints now come out with a shiny surface where it was against the packing tape and they just pull off by hand with just a bit of effort.

When I was able to just pull the print off by hand with just a little tug, I almost cried because of the trauma I have endured over the years stabbing myself with razors and putty knives trying to remove prints.