Bed mechanical bending/deflection

Hello,

I'm building a printer and I want to give it a large-ish bed, but I'm looking for some expert advice as to what material to use to support the bed (not the bed itself). I'm worried that, with a 380mm distance between supports on either side of the bed, it's going to bend if I don't give it some sort of MDF or aluminium support (equivalent of the "frog").

I've got two z-axis support columns (threaded screws on both sides + 2 smooth rods on one side for stability) with printed supports 160mm wide., and I wanted to suspend the bed on screws, 3-point style. Ideal size of bed support would be 380x340.

I know next to nothing about mechanics of materials. Could someone advise as to what material would be best for this (weight and cost), and what thickness would be required to stop it bending in the middle? Alu plate at 3mm would probably weigh about 1kg at this size. Would MDF at 3mm or 5mm work?

Thanks in advance,

Arut

PS: Bed itself would probably be heated PCB

Edited 1 time(s). Last edit at 03/15/2015 12:53PM by aruta.

There is very little force applied perpendicularly to the heatbed, and usually the PCB is covered with a 3mm piece of borosilicate glass, so the deflection in the middle is really minimal and I don't see it as being a concern, but of course I may be wrong.

MDF is glorified cardboard, and at 3mm thick, it IS cardboard.

Try using a frame made of steel or aluminum square tubing. Over the distances mentioned, neither will flex enough to be a problem.