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Heated Print Bed and Issues

Posted by tjhj2 
Heated Print Bed and Issues
November 12, 2012 09:45AM
Hello All.

So I made a Heated Bed for the Tantillus, but then I encounter an interesting problem. With other heated print bed designs, there is room/mounting solution for fans to allow the part to be cooled on the surface to prevent curling of the PLA. As far as I can tell, it seems that there isn't enough airflow over the part top to stop the curling from the heat. I am thinking of maybe a hose and nozzle that would direct cooling right below the nozzle. Any suggestions or ideas?

Here is my design. I decided on a 100watts to test, because with the side fan airflow passing over and under it, I figured it would be harder to keep it very hot.
To get this I went with 30 AWG Nichrome Wire. Each strand is 10". Four total strands.
This gives each length a resistance of 5.75 ohms. Wiring all of them in parallel gives a resistance of 1.43 ohms. At 12v this takes 8.4 amps is 100.69 watts.

To spread the heat, I recut the upper acrylic plate out of 1/8 in aluminum plate.

This results in good heat, it heats up in under 1 min, and holds 70 deg C with a reasonable off time.

NOTE this runs the wires a little too hot, it has started to char the insulation where it is not in perfect contact with the aluminum plate, I would recommend trying 3 10in leads for 75 watts.

So here is some pictures and a clip of it working... well kind of working.
open | download - warping issue.JPG (82.8 KB)
open | download - Installed.JPG (126.3 KB)
open | download - Wire Layout.JPG (139.2 KB)
Re: Heated Print Bed and Issues
November 12, 2012 04:15PM
Looks good. On most machines people would put a fan shroud around the nozzle to cool just what they are printing but that is not really possible with Tantillus's carriage. This is why I tried making the air ducts to blow just across the layer being printed and the thermal barrier of the hotend. I only made the ducts for 40m fans and they did not work as well as I wanted. If you can design one that produces laminar air flow directed across the tip of the nozzle and the thermal barrier it should solve the problem. Or you could try a 25mm or smaller fan mounted to the carriage.

Have you seen if it will reach 110c for ABS?

Are you running two power supplies?

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Re: Heated Print Bed and Issues
November 13, 2012 10:46AM
Ill see what I can come up with for some ducts.

Have you seen if it will reach 110c for ABS?
Yes, it takes 4 min 30 seconds to reach 110c. This is a surface calibrated temperature. It would seem that it could maintain 110c with no time limit, it is running about 70% on time which should give ramps and the wires time to cool down. I ran it all the way up to 125c just to test and held just fine, but it getting close to 100% on time.

I reprinted almost all of the parts in ABS to make sure they didn't melt get soft. But ABS and I don't really get along very well.

Are you running two power supplies?

No, I am running one ATX computer power supply. An Eagle Voltas ET-PSVT500 500Watt ATX12V Power Supply, with a 5ohm 10watt resister on the 5v line to provide some load balance. It looks horrible, but it's a cheap solution to a lot of power.
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