Having successfully made one Mendel z-leadscrew-base_2off as an experiment to try ABS on a vacuum bed, I decided to make the second from PLA to see how well that works on a vacuum.
Three of the corners lifted very slightly during the build (about 0.2mm) but not enough to matter except to a perfectionist.
When the object cooled it did not break the vacuum, unlike ABS. The part was still easy to remove though.
The base is flat apart from the corners and a few shallow dimples.
The quality was very good with no clean-up at all. I recently discovered a simple bug in all my builds after I moved away from 0.5mm filament. With 0.3mm and 0.4mm filament my layer height was 0.24mm and 0.32mm respectively. The problem is my z-axis only has 0.05mm resolution, so layers alternated in height, none of them being spot on. That caused the sides of my objects to not be as flat as they should be as the filament width varied from layer to layer. I now use 0.375mm filament giving a 0.3mm layer.