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adding another heated bed

Posted by galaxyman7 
adding another heated bed
August 10, 2012 12:15AM
Ok, so I have a printrbot, and I am printing with weed trimmer line, which needs a bed temperature of around 150 C so it doesn't warp. My current heated bed, which is a pcb, can only reach around 110 C. Do you think it would be ok to add another bed underneath it, powered seperately? Basically this one would be manual control, with a separate power supply, and the fine tuning would be done by the existing heated bed. Does anyone know if the the pcb and thermistor can handle 150 C?

Either that or I somehow ramp up the amount of power going through the heated bed, but I am afraid that the pcb is not meant to take that much current. If I do add to the power, how would I do this? Would I power it in parallel with another supply?
Re: adding another heated bed
August 10, 2012 05:57AM

Does anyone know if the the pcb and thermistor can handle 150 C?

Most likely, yes.

Adding more power either requires to raise the supply voltage - if your electronics supports that - or a different bed with thicker, shorter tracks: [reprap.org]

Generation 7 Electronics Teacup Firmware RepRap DIY
Re: adding another heated bed
August 10, 2012 06:57AM
Well I just tried setting my heated bed to 130 C, and it actually did get there eventually. It probably took around 15 min. It definetlely helps a ton with warping. I printed a 3 inch long piece with a small amount of warp, where as with the 100 C bed the part would be unusable. I think adding a small heater pad to the bottom of the board wil do a lot of good by boosting the max temperature of the board. I have a feeling at 150 C the parts will be completely flat. Also, I will try printing with a brim, and see if that totally eliminates the warping. Thanks for the help.
Re: adding another heated bed
August 10, 2012 09:22AM
I would try adding high temp insulation under the PCB to make sure the bulk of the heat is driven through the glass and not lost out the back of the PCB. I probably wouldn't advise trying to run more power through the PCB as you could burn out some of the traces.
Re: adding another heated bed
August 10, 2012 09:24AM
This sounds interesting, please keep us updated on the results.

Do you happen to know what kind of plastic the weed trimmer line is made of (Nylon, I assume), and could you post information about the type and brand of the line, printer settings, pictures of the printed results, and other relevant information? I haven't heard of anyone using weed trimmer line before, but it sounds very useful as it is cheap to come by. Also, how bad is the smell of the extruded material?


Apparently nylon releases cyanide hydroxide if the temperature goes more than +-10'C above the melting temperature, watch out for that!

Edited 1 time(s). Last edit at 08/10/2012 09:36AM by Lodorenos.
Re: adding another heated bed
August 10, 2012 10:05AM
I have the standard Prusa PCB heated bed, and I was able to get it up to 150C. I do have the back side of the bed insulated, and it took forever to get there, but it made it. You could up the voltage to the bed a little bit and it would heat up more quickly, but I wouldn't push it too far.
Re: adding another heated bed
August 10, 2012 05:22PM
I think I will do that in addition to buying a small heating pad. This way the bed can warm up quicker.


Brand of line:

Slic3r settings:
layer height 0.4
skirt loops 15 at distance of 0.4 (a brim)
2 perimeters
0.4 fill density
retraction length 10 mm
lift z 0 mm
speed of retraction- maximum possible (i think around 900 mm/s)
extra length on restart: 0.5 mm

slow down if layer is below 10 s

nozzle diameter 0.5
filament diameter 2.65
extrusion multiplier 0.95
temperature 245
bed temperature 130 (preferably 155 in the future)

60 for everything except small perimeters which are 35
travel speed 300
bottom layer speed ratio 0.5

I print on blue tape, which seems to work very well. I also have a metal plate over my heated bed so I can hold the part down with magnets around the brim. One note, you need to dry the filament before using it or you will get lots of steam coming out and it will make your extrusion all bubbly. I do around 300 F for 4 hours in a toaster oven i got from the thrift store. After this, the filament should extrude very nicely.

The plastic is Nylon, and I know that it can emit hydrogen cyanide, but in miniscule quanities. The only way it will start to emit large quanities is if it starts thermally breaking down at much higher temperatures. Just turn on a fan and you will be fine. As for the smell, I would say it is around the same "amount of smell" as ABS.

I will post some pics later today showing the latest print quality.

How long is forever? It would be nice if all I had to do was add insulation.
Re: adding another heated bed
August 10, 2012 05:42PM
Ok sorry for the bad quality but here are some pics of a lid I printed. The last pic is of the bottom of the lid.

What do you think about these:

Do you think it will get me up to 150 C with both heaters? And how should I power them?

Edited 2 time(s). Last edit at 08/10/2012 05:54PM by galaxyman7.
open | download - photo.JPG (278.3 KB)
open | download - photo(1).JPG (288 KB)
open | download - photo(2).JPG (223.8 KB)
Re: adding another heated bed
August 11, 2012 02:22PM
There are larger and longer heated beds now available on eBay.
Re: adding another heated bed
August 12, 2012 07:09PM
I think I will just make a heated chamber. It will make the bed hotter due to less heat loss, and it will help with layer adhesion. Hopefully the chamber is enough to get the temperature up from 130 C to 150 C.
Re: adding another heated bed
August 13, 2012 05:21AM
Before doing that, make sure you take into account the fact that electronics (including the NEMA steppers) will degrade more readily in a hot environment. Also, the metal rods will increase and decrease in size slightly with the temperature change, which might cause inaccurate prints.
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