Thanks to Kim's suggestion I bought some dibond composite sheet to make a flatter support bed (thin alloy sheets either side of a plastic core).
But I made the mistake of ordering A4 sheets as I thought that would be big enough.
A4 is 210mm x 297mm.
Standard bed is 214mm square.
So I bought a new A3 panel. Unfortunately when it arrived it was not flat.
I then did a bit of lateral thinking and I recon I can make a three point support bed using the original A4 panels.
Attached is my design so far, but I have not yet cut it out and tried it. Hopefully that will happen later this week and if it works I'll upload the DXF for others to try if they so wish.
I have made the panel larger than the original and brought the outer holes in from the ends as I thought they could do with a but more support.
You can see the A4 size is overlaid.
The 50x50 square is just for me to measure and scale as printers don't always print 1:1.
