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Heated bed; 8 mm thick 420x420 mm tooling plate

Posted by HugoW 
Heated bed; 8 mm thick 420x420 mm tooling plate
April 09, 2019 01:19PM
Hi,

finally after converting my MKS junk board to Marlin 2.0, I have a very well functioning printer. It spits out PLA by the kg / pound / mile / km (as prefered) and it's fast, acurate and it makes me and my kids happy. But, now I notice my old PLA stack is getting too old and the stuff printed becomes brittle and unusable. I print RC car parts and the parts printed a year ago now crack easy under the pressure of mounting them. So, I have been looking into PETG and I love it. For smaller parts I can use it without heated bed, but now I notice printing bigger parts does not work well. Too much warp. So I need to add a heated bed. My bed is aluminium tooling plate with painter's tape on it. The PLA needs a bit of glue stick assistance, the PETG does not.

So, how will I heat an 8 mm thick, 420x420mm plate (6,5 kg)? What power is required? I run 24V= but I guess I should go to using the 240V~via a solid state relais or something like that, right? Also the bed will lose heat rapidly and I don't want to waste energy, is there a proven way to isolate the underside, not to lose heat there?
Another choice would be to go to a glass bed, again tape covered, and use the 8 mm plate as mounting base?

Any solution is wellcome (I don't consider gas heating...) and good examples I can steal from are appreciated.

Thanks,

Hugo
Re: Heated bed; 8 mm thick 420x420 mm tooling plate
April 10, 2019 09:05PM
An AC heater with a SSR will be faster on the heatup. I use 2 200x300 keenovo heaters on my 300x400 bed heating 1/4" MIC6. [www.amazon.com]

Edited 1 time(s). Last edit at 04/10/2019 09:05PM by Stephen6309.
Re: Heated bed; 8 mm thick 420x420 mm tooling plate
April 11, 2019 10:10AM
If memory serves me correctly, Keenovo will custom make bed heaters also if you contact them. So you should be able to get a single AC powered heater for your bed.
Re: Heated bed; 8 mm thick 420x420 mm tooling plate
April 11, 2019 10:37AM
Check this site to calculate the heat-up time based on the bed size and heater power applied.

For that size bed, line power is the way to go, as you will quickly realize when you calculate the heat-up time. Add a one-shot TCO to the heater to prevent fires, use electrical fuses, ground the metal plate.

Keenovo makes good quality heaters and will custom make them for reasonable prices. The 468MP adhesive that comes on them is good for about 2 years of temperature cycling before it starts to let go of the bed plate.

Adding insulation to the underside of the bed/heater isn't really necessary unless there's something under the bed that needs to be protected from the heat. Adding insulation may speed heat-up but will also increase cool down time. If you want to print ABS, the heat "lost" to the air by an uninsulated bed will warm the enclosure, so the heat isn't wasted.

The bed plate is going to expand when it heats up. Your leveling system should allow that to happen without forcing anything to bend or flex. Here's the 300x300x8mm bed in my corexy printer. It uses a kinematic mount that allows expansion, and is so stable that I don't have to relevel it unless I take apart the Z axis to make modifications.


Son of MegaMax 3D printer: [www.instructables.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
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