The print bed will be from previous Giant printers - 500mm x 500mm x 5mm aluminium plate with mains voltage silicone heater pad underneath.  I want to make this latest version of the printer capable of covering the whole of the print bed if possible.  The bed will be supported by a plywood sheet itself supported by an aluminium extrusion frame attached to the C-Beam double gantry plates.  Between bed and plywood I plan to have 12mm thick PU foam for insulation and to ensure the heater pad is touching the aluminium plate (the glue has given up in the central region).  The C-Beam will be 1000mm giving a printing height of just over 800mm.  NEMA23 stepper motors will provide the drive.

Amazingly, I have found a PEI sheet big enough for my Giant print bed :-  PrimaFil PEI Ultem sheet 500x500mm-0.2 mm  and with the pound dropping fast against the Euro I've decided to get it now.  It can go on the aluminium print bed to provide a better printing surface than plain aluminium while cutting out the glass plate will greatly reduce the weight.

I look forward to seeing how this goes. I have a Sidewinder X1 and the AC bed is reall good.

The lights dim when I run the mains heater on my Giant printer 🤣  Well, not quite but it is 1.2KW which is more than a bar of an electric fire. 

Having tried PEI sheet on my Concorde printer with unsatisfactory results, I'm now not sure about using it on the bed of my Giant printer.  I didn't do very well with plain aluminium for print adhesion though and unless I can adjust print settings to make plain aluminium work I shall definitely try the PEI.

I'm no longer sure about using the C-Beam and Gantry Plate system in view of the cost mainly though if I decide to change the Z axis on the Concorde I would have most of the parts to transfer from Concorde to Giant.  The Concorde printer Z drive system does not appear to be performing as well as I had expected though I'm not sure the rail system is the cause, I have some investigations to do.

A bed weight of several KG would be better supported on 3 threaded rods I reckon and guided with metal wheels on two 20mm x 20mm V-Slot extrusion rails.

That's pretty much how my D-Bot is. The wheels are on diagonally opposite corners. With a heavy bed it's best to use 1mm pitch screws to avoid 'back-driving' when power is removed or z motor(s) de-energised. That's assuming 1 motor per screw. If just 1 motor with screws driven by belt/pulley arrangement then steeper screws may be ok. 

My screws are 1mm pitch.  I plan to try with one motor and belt/pulley arrangement.

@tekkydave and anyone else interested...   Thinking about this again.  The Z drive on the Concorde is working very well now and would be a simple Z drive for the Giant printer.

@tekkydave

Judging by the Z drive in the Concorde printer with standard NENA17 stepper motors, I think NEMA17 will be strong enough for the Giant, at least the longer ones, which I also have.  I can use the same case as before with aluminium extrusion and acrylic sheet.  I see no real reason to change ATM.  The C-Beam Linear Rail would be less than a metre high as the Z drive would be below the XY plane like with the Concorde.

Cost of the C-Beam and gantry plates comes to just under £100.  Then I would need to see what V-Slot wheels I have plus a few other bits.  At least these parts are available from a UK supplier and in stock - at least ATM.  All food for thought...