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Need advice for material to use under hot plate

Posted by fxmech 
Need advice for material to use under hot plate
May 28, 2013 01:54PM
I am building my heated bed.
I have a 12X8 1/4 thick Pyrex glass top
a 12.25 x 8.25 PCB hot plate (MK1)

The problem is that it has a slight bow to it and I need to sandwich it against something to get it to flatten against the glass.

I was going to use 3/16" thick aluminum and design in some aluminum edge clamps that grip the very outmost edge of the glass and press it against the aluminum plate beneath the heater.

Is aluminum the best way to go or is there a better material. I know aluminum absorbs a lot of heat so I would think it would make the hotplate more inefficient.

Should I maybe use 1/4" think phenolic or some other material beneath the hotplate???
Re: Need advice for material to use under hot plate
May 29, 2013 12:42PM
Hmm, I think aluminum pressed against the bottom of the heater would suck a bunch of heat away, and would add a lot of weight (assuming you're using a Prusa-style printer with a moving bed). I just attached the glass to the heater with binder clips at four corners, and attach the heater to the bed plate (mine's MDF) with about a quarter inch air gap between the heater and the plate. The binder clips get it pretty close to flat against the glass, and the air gap is enough insulation that it works fine. Perfectly level contact between the heater and the glass doesn't appear to be necessary.

However, if you really want something in there pressing the bed against the glass, I'd go with an insulator. Example: [hydraraptor.blogspot.com] This is a custom bed, and probably too heavy for most printers, but the wool carpet underlay would act as a good insulator, and if you pack it in there it'll press the heater against the glass without adding the heat sink and weight of aluminum.
Re: Need advice for material to use under hot plate
May 29, 2013 01:21PM
I use 3 2mm cork sheets to insulate bed. works quite well, and is very cheap.
Re: Need advice for material to use under hot plate
May 29, 2013 07:50PM
Thanks both are great ideas... McMaster carries cork and wool cloth for insulating... will see which has better characteristics but that will work just fine. Im building a pretty heavy duty printer so the aluminum plate is to get a good flat and solid foundation.
Re: Need advice for material to use under hot plate
May 30, 2013 02:52PM
Cement Board from your local hardware store.

(Otherwise known as tile backing)
Re: Need advice for material to use under hot plate
June 01, 2013 01:30AM
For insulation, I use this fiberglass paper from mcmastercarr..

[www.mcmaster.com]

You kinda have to buy a lot at a time, but it seems to work really well.. with one 1/8" layer, I can comfortably lift my heated bed assembly when it is at 100 deg C on the surface..
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