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simspeed
My aluminum bed is 560 mm by 760 mm for a printer I'm building. I made it out of 8020 v-slot extrusions. I used ni-chrome wire looped inside to make the heater circuit. It heats to 110c using 120v mains power. I built it on a stainless steel kitchen cart. I'm having some bearing shaft parts made to tie the dual Nema 23 Z axis motors together for the Y gantry. I just finished tying the dual Nema 23 X motors together to synchronize that axis. The Y axis uses a single Nema 17 motor. I have it all broken down waiting for the machined parts before the final assembly.

[attachment 57344 Heatbed2.JPG][attachment 57343 Heatbed5.JPG]

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simspeed
If you have a high temp heated enclosure....do you even need a heated bed. I had a few small ABS parts printed locally on a Stratasys printer and was surprised to see that the print bed plates are made from ABS. No heat bed but the enclosure is like a sealed oven. He said the plates are reusable for quite a number of prints and they only cost about $5 to replace.

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atunguyd
The 8 bit issue is not correct, if you look into the Marlin firmware you will see that there is copious amounts of double and float declarations. This makes the poor Aurduino really slow but still allows it to support large numbers. On the aurduno the float can support up to 7 digits so it is possible to address up to 1km (1 000 000mm) without decimal points and 10m (10 000.00mm) using two decimal points. Likewise the double can address up to 1km distance as well (no decimal points).

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thetazzbot
I have a question for the OP. Will you always be printing such huge items?

The reason i ask is that for the complexity and size the payoff is not proportional. For example if i were printing tons of smallish parts i would rather go with multiple printers for redundancy and parallel printing.

Or a printer with multiple print heads to print simultaneous duplicates. Curious abot the usage of such a beasty printer :)

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dc42
As Jason says, for large heated beds the practical option is an AC mains powered bed controlled by an SSR. The company he linked to will make a custom silicone heater to your size, voltage and power specifications at a very good price. I use a 230V 350W 300mm diameter one from them in my delta printer. Choose a heater slightly smaller than the bed to leave yourself a margin (e.g. 15mm) at the edge for fixing screws and bed clips. Total heating power of 5kW per square metre is about right.

For the solid state relay, the Fotek SSR-25DA is inexpensive and should be adequate if your heated bed current is up to 10A, or SSR-40DA if it is higher. Depending on the current, the SSR may need a heatsink.

Using an SSR to control the bed will also get around a design flaw of the RAMBO, which is that the heated bed MOSFET is badly chosen - it can't be relied on to have a low Rds(on) with only 5V gate drive.

If you use an AC mains powered heater, you need to take additional safety precautions - in particular, protective grounding of the bed and any other metal parts in the vicinity. Powering the printer via an RCD would also be a sensible precaution. If the bed is moving, then you must use appropriate highly-flexible cable to connect it, and provide strain relief at both ends of the cables.

PS - I think you are taking a risk using an 8-bit controller board for such a large printer, because the software for such boards typically uses 16-bit variables for most quantities, and these may overflow when the distances get too large. Somebody building a large delta printer recently had a problem that probably has this cause. As you are spending so much money on the printer, it really makes sense to use a 32-bit board. You would also get a much faster USB link, and in most cases, an Ethernet port and a built-in web server. If you insist on using an 8-bit board, try to get confirmation that someone else has used the same firmware to control a large printer if the same configuration.