Larger Bed (420x420) - Will this work?

Hi all,
I'm currently in the planning stages of my next printer and I'm looking at having a 420x420 (or even 500x500) hot bed for my next printer build.

What I'm curious to as can I power 4 PCB hot beds using dedicated power supply (24v 60a) with a relay fed from the printer controller PCB to switch them on/off, using one centered thermostat to read the temperature of the bed? (as per the attached picture)



The bed will be an aluminium plate (probably 4 or 5mm thick)

You would be better off using a silicone heater. This company [www.aliexpress.com] will make one to your own size, voltage and power specifications, at a good price.

For a bed of that size, consider using AC mains to power the heater, through a DC-AC SSR. You need to take additional safety precautions (grounding, insulation, and cable strain relief), but it avoids the need for a large power supply.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

thanks for the feedback. My only concern with those is being in Australia we have 240v AC but if I put in a GFCI that should add a secondary safety step in case of line damage. How are these compared to the PCB type heaters?

I don't think 4-5 mm is going to be thick enough- at that size it will sag under its own weight. Plain aluminum sheet is not flat, either. Look for cast tooling plate. It is milled flat.
This is what a 317 x 305 x 6.35 mm tooling plate does at room temp: [vimeo.com] and at print temperature [vimeo.com]
I think it is safe to assume that a 500 mm plate will sag a little more, which may be OK depending on the first layer thickness you plan to use.

The plate in the video has 0.5W/cm^2 heater (450W) that heats it up to 105C in about 5 minutes. You are going to want similar areal power density or you may be waiting a long time for things to heat up.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Thanks for the insight. What thickness plate plate would you recommend? Would it be worth going to 8mm thick or would that be pushing the weight factor too much? I'll be planning on running leadscrews with anti-backlash nuts for drive the bed (im push more for accuracy and print quality then speed with this build), somewhat like your printer but with a 500mm3 build size.

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Bundybear1981
thanks for the feedback. My only concern with those is being in Australia we have 240v AC but if I put in a GFCI that should add a secondary safety step in case of line damage. How are these compared to the PCB type heaters?

I agree, a GFCI (or RCD as we call them here in UK) would be a good additional safety device.

Silicone heaters can provide much more power than PCB heaters, giving you faster heating times. My delta has a 330mm diameter aluminium bed plate with a 230V 350W 300mm diameter silicone heater attached to the underside. It reaches 100C in less than 5 minutes.

One thing to watch for is that if you use a silicone heater with an embedded thermistor as I do, the thermistor will over-read due to its proximity to the heater wires. A thermistor in direct contact with the bed plate would be more accurate.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Hey Bundy
If your looking for tooling plate Calm Aluminium in Sydney have ATP5 and will cut to size. They have 6.35 and 7.9 available when I called this week

Cheers

Thanks for the reply, unfortunately I'm up in Bundaberg, QLD. I'm not sure how well it would fare in freight..

I ordered a silicone heater mat from ali, just waiting on delivery for it now. Was just under A$70 for a 240v 500x500 850 watt heater.

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Bundybear1981
Thanks for the reply, unfortunately I'm up in Bundaberg, QLD. I'm not sure how well it would fare in freight..

I ordered a silicone heater mat from ali, just waiting on delivery for it now. Was just under A$70 for a 240v 500x500 850 watt heater.

Yeah figured by the name you may have been bundaberg based, I'll be getting mine freighted to Canberra as it seems impossible to find tooling plate locally

Be keen to see what you think about the heat pad when it arrives, I've asked them to quote on a 1000w/1200w 240v 500mm round one

Cheers

Edited 1 time(s). Last edit at 04/08/2016 09:01PM by aussiephil.

Funnily enough, I'm an Aussie from Brisbane and I had this exact same idea. I ended up going with a silicone mat with a SSR because the management side of having four separate MK2B or MK3 beds wasn't worth the effort.