Ideal Material for Heated build-bed

I'm trying to design a heated build platform, and was wondering if any of these material below have been tested as a suitable printing face, I know some of them will thermally insulate, but I was thinking about a thin layer as the top (removable) surface-

Acetal - (Delrin) -

Tufnol -

Polycarbonate -

Annodised Aluminium -

Galvanised Steel -

Limestone / Marble (Like a polished tile) -

I'm thinking about making an Aluminium base then PTFE sheet (sandwich) with cut-outs for Peltier modules and the thermistors then another layer of Aluminium on-top as the heater plate, but I was thinking about also adding a 1mm layer of Polycarb as the removable build surface, can anyone see any obvious problems before I start cutting stuff. I expect the total layer stack would be about 10-12mm.

I can see most people are using Kapton tape, has anyone used a thicker layer sheet, or would only be usable once, so better stick to tape?

Also has anyone built a successful Peltier based build platform? and one with multi-heat zones (independent control) for small and larger parts? Has anyone done any analysis of the part density or size to build base heat requirement?
Is anyone using multiple thermistor on a heated build platform?


My build platform is going to be 510 x 250, but I'll explain that in another thread as it's another experimental idea...

I have loads more questions, but I'll stop there for now.

Thanks.

Rich.

Kaptan can be used dozens of times without reaplication as long as you have a temp controled plate. Mine is still going strong after 40+ plates.

I use ceramic as the heater, and stainless covered in kapton as my plate. Alllows for very quick swap out (only take 2 minutes for the new plate to get hot).

Nophead I think is currently using Acetal.

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repraplogphase.blogspot.com

I wouldn't go for a peltier - they're expensive and unless you're using them to rapidly cool down the part afterwards probably not worth it. My setup is masking tape over aluminium for pla, though I'm going to move to kapton because it seems to work well for others. Raw aluminum/steel/marble probably won't stick well enough. Aluminium conducts heat so well that multi-heat zones probably won't save a great deal of power as long as you insulate below the bed well, even with the 2mm totally uninsulated alu i'm using the edges of the bed 5cm away from the heaters are only about 5 degrees cooler.
[jamesreprap.blogspot.com]
is my setup, if I were you I'd start with a much simpler design like that, it's cheap and has a much smaller thermal mass than a 10-12mm thick stack so it gets up to temperature very quickly.
As for the power requirements, it's not too hard to calculate in theory if you make a lot of assumptions about heat loss, but tricky if you want an accurate answer. Either way, it's not a bad idea to be able to have a maximum power far greater than the power needed to hold it at temperature so it'll rapidly heat up. No guarantees, but if your heating elements are well thermally coupled to the bed, I've found you can use more than their rated power initially because the maximum rated power is often because they'll break if they get too hot, which won't happen to start with because of the bed acting as a massive heatsink.

Yesterday I increased the size of my heated build platform (10mm on all sides) on my Makerbot with a piece of polycarbonate...it works great! I scuffed it up a lot and put on some PET tape (green) that Spacexula told me about. I then applied 2 layers of PET tape ontop of the polycarbonate (which is .93" Lexan) a sandpapered that a lot too...and I can now print Wade's Geared block and it snaps off so easily....much better than Kapton tape.

So polycarbonate makes an awesome heated build platform with PET tape!

Thanks everyone.

I'm going to make a simple bed as sugested, Alu and some metal clad resistors.

I may try Tufnol (1mm) as a top build surface as it seems to have the same or better thermal conductivity as Kapton.

I'm still a while away from a working machine, so if anyone can test Tufnol I would be very interested to see if heated ABS sticks to it?

I read the maximum working temperature of Tufnol is only 120C. I run my bed at 140C and extruder ABS at 255C onto it, so I don't think Turnol fits the bill.

Thermal conductivity is not really an issue when you use a thin film.

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[www.hydraraptor.blogspot.com]

Very good point Nophead, I expect I'm looking to solve a problem that's already solved.

140deg - is much hotter than I expected to be needing, Do you need this surface temp to transmit enough heat up the layers of the part being printed?

Could you not use a modified heatgun and some sort of round barrier around the object being printed then try to spin the hot air in a sort of vortex so it keeps the ABS hot and takes the stress out.
Or is that just a bit mad or too simple.

Or maybe put the hot air flow around the extruded and have a similar air containment or hot cyclone. I guess you need to be careful to not overheat the extruded with trapped hot air...

I still can't quite grasp why it sticks to Kapton at the moment. Anyone have a scientific or not explaination.

I need a 140C bed and 255C plastic when extruding the white ABS I got from reprapsource.com in order for it to stick to the bed. After the first layer I drop to 110C bed and 240C plastic. I can do natural ABS at lower temperatures but I would expect the bed to be scared if it could not withstand 240C. Hence Kapton or PET, as both are high temperature plastics.

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[www.hydraraptor.blogspot.com]