Rethinking Bed Heat

I am currently experimenting with various methods to produce large ABS prints. There seems to be two issues with ABS: 1. Getting it to stick to the bed, and 2. Not warping.

It seems to me that if I can get the ABS to stick without bed heat that this would reduce warping, but maybe I am missing something.

My theory is that on a large print that each layer will cool to the same temperature as the bed making each layer uniform.

The only other option I see is to try to raise or maintain the temperature of the entire item as it prints. The bed can only heat a few layers, which means that as the part gets taller it will get cooler making a heated build chamber necessary.

Anyone do experiments on this or have an opinion?

G’day all. I’m a newbie and finding this forum is good value.

I’m thinking the K8200 is good value but my biggest gripe is the print bed - it warps by a few mm over it’s width.
I’ve inverted the board (circuit tracks up to get them closer to the action) and put a sheet of glass over it.
Between the PCB and the glass I’ve put 10mm strips of thermal transfer tape around the perimeter (this provides a consistent depth (0.5mm) for the ‘well’ that’s created (to be filled with thermal paste). The thermistor near the centre of the board stands proud by about 0.7mm so two layers of tape (1mm total) (with a suitably sized hole) were laid over it. I used a straight edge to ‘screed’ the paste flush with the surface of the tape - still some air present (maybe next time I’ll get it perfect) but the bed is now FLAT. I may put some silicone around the bed to ensure that the glass doesn’t push away from the board.

My next (immediate) improvements will be to add more insulating layers under the bed and to implement a 24V power supply to speed up the heating cycle/increase the bed heat.(Much discussion on this here: http://forum.velleman.eu/viewtopic.php?f=53&t=9598) Thanks for sharing!
My preference is for a separate supply and a solid state relay to switch the bed.

Ian