Thick Sheet Material, which one?

I am looking at choices for the thick sheet matrial to make the bed of a Prusa Mendel.

The choices I have available to me are

3mm Alum.
5 mm Alum
4mm Dibond
3mm lexan
5 mm lexan
MDF

I am wanting to mount a PCB heated bed on top.

Given the choice any suggestions on which material to go with

regards

Graeme

I use 1/4 inch acrylic. Now at one point, before I got my heated bed (PC, I tried using a hot air gun to keep parts warm while printing, and the bed warped a bit. I put it between two pieces of granite tile after heating everything with the gun, and it was then straighter than ever, so that was good.

When I got my heated bed, I was a little concerned that the heat would also warp the acrylic. I took some 1/2 inch pieces of PEEK rod, and drilled 5/16 inch holes in one end, into which I pressed some rare earth magnets. Using the heat bed PCB as a template, I marked holes in the acrulic bed, and drilled 5/16 in holes there as well. After matching the polarity on each magnet, I pressed four more into the acrylic.

The heated bed is simply glued to the top of the PEEK posts with epoxy. Looking at it now, the PEEK is probably overkill, as the corners of the PCB don't really get too hot. Good news is that 1/2 inch is plenty of clearance, and the acrylic is not warping.

How do you keep the PCB flat if it is only supported at the corners? I have a PCB heater from reprapsource, but I have never figured out how to use it.

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[www.hydraraptor.blogspot.com]

I think I read that Prusajr glued his PCB on the bed using multiple cork spacers. I as concerned about flatness too so I placed my PCB under the aluminum bed sandwiched between the bed and the printed springs.

I made a heated bed a long time ago, and made it for the rapman. Here is the link on thingiverse [www.thingiverse.com] . BTW it works better with kapton on top rather than the back side of board (no copper on this side)

i did not use it long, because it cracked its surrounding support because it was glued in. I would recommend that the heated bed be taped down, or bolted loosely with slightly undersized bolts so there is at least 1-2mm room for expansion. Also it is acrylic and now has some warping.

The best material for the base from what I see from your options seems to be MFD board with a PCB board on top and taped. It will act as an insulator and will keep its general shape as it dries out. I have used MFD and particle board and both last a surprising long time compared to the acrylic beds. Even the thicker acrylic beds warp over time.

Again this is from my own experience, your mileage may vary.

Edited 1 time(s). Last edit at 05/13/2011 11:59PM by jamesdanielv.