Well, I gave it a go but no-go, The other side of the bed has a layer of magnetic rubbery stuff which the print surface sticks too. This lets it to spring when clamped to the mill table. Also when it cuts through the grey layer the aluminium tends to grab the tool making it deeper at that point.
All rather sad really. I have other bits on the way, including 3mm aluminium and sticky magnetic sheets good for 130C continuous, so it was always going to be a stopgap. Also have a spring steel pei coated build surface on its way.
Could use 4mm, as you suggest but the extra weight ~150 gms (around the same weight as the silicone heater) would slow down the action even more. Just feel that 2mm aluminium is too flimsy. Original bed weight inc heater but no wires is around 560gms excluding print surface. Weight of bare aluminium sheet is 447 gms, so I reckon original bed heater is ~60 gms, allowing 50gms for magnetic rubber.
Well at least I found out why people dont do it that way
![:(](https://madmodder.net/Smileys/default/sad.gif)
Best Regards
picclock