3D printing guides: Everything about heated beds!

Hi everyone, i’m Tom, and two days ago,
i wrecked my voice. I’ll try my best to be comprehensible today, but, as always, if
you’re having trouble understanding my spoken words, feel free to turn on subtitles, those
usually have the full script i use / in there and should be pretty accurate.
But anyways, today’s topic is going to be heated beds, that has been one of the most
requested topics, so today i’m gonna tell you all about them!
So, heated beds have one very obvious main purpose: And that is to get the surface of
the print bed up to a temperature where the print will stick to it better and, as such,
will not come loose from the unavoidable warping forces that the layer-by-layer printing process
generates. But a heated bed has a second side effect that can help reduce warping at the
source, and that’s because the radiated heat will help keep the print warm. You see,
that largest factor in how much a print is going to warp is, roughly speaking, the difference
between the plastic’s glass transition temperature and the “cooled down” temperature during
a print. So either, you have PLA with a low glass transition temperature of 50°C and
let it cool down to 20° with an unheated bed, or you use ABS with a glass transition
temperature of about 100°C and just make sure it doesn’t cool down as far. The extreme
case of this would be a heated chamber, which keeps your ABS print at 60 to 80°C, so you’d
end up with the same 30° temperature difference. Heated chambers or at least enclosed printers
are extremely nice for the high-temp plastics, but that’s an entirely different topic.
Now, because of those two effects, i still haven’t found a plastic that is not easier
to print with a heated bed. I mean, sure, you can print PLA on blue tape and some of
the soft plastics onto glass and such at room temperature, but even for PLA, having the
option of heating the bed surface and printing straight to glass is just so much more convenient
than having to pry your prints from blue tape. Of course, heated beds are absolutely neccessary
for some plastics, like ABS, which can be printed onto a cold surface, but that involves
a whole new level of kludges. As far as the heated beds themselves go, there
are two basic types that you can get. One is the classic PCB heater, originally designed
by Joseph Prusa, which was the first heated bed that you could buy. Along with the Prusa
Mendel, it basically established the mid-size form factor of a 200 by 200mm build platform.
You can still get heater PCBs that are very close to the original design, some of them
can now be switched from 12V to 24V, others have different form factors, like the round
beds intended for Delta printers. But there’s two issues i personally have with heater PCBs,
and those are, one, it can be pretty hard to get them to make good contact with whatever
sheet material you put on them, which becomes necessary, because, two, they have a tendency
to warp and bulge, especially the cheaper and thinner ones. As the controller applies
power to the bed, the side with the heating tracks heats up much faster than the opposite
side, the PCB expands on the hotter side, and in the process of that, bows the entire
print surface. In fact, one of my first big mysteries with my back then Prusa i2, was
that the second layer just wouldn’t stick onto the first one. And as it turned out,
because i was reducing the heated bed temperature for all layers but the first one, the heated
bed would shut off for a while until it reached that cooler temperature, and, you guessed
it, bowed away from the nozzle and basically left a huge gap between the first and second
layer. So, the other option, which i like a lot more,
are heater mats that you can stick onto the bottom of your print sheet, in my case, aluminum
because i also use an inductive probe for bed auto-adjustment. You can get these heaters
from a few resellers in Europe or the Americas, but you can also get them directly from the
guys that make them, at any size, voltage and power rating. For example, i had this
one made as a 150mm square with 150W, which will take it up to 150°C. More than enough
/ even for printing polycarbonate. I also have a 300mm round bed incoming that is made
to run at 230V mains power, since shoving 600W through a power supply is kinda pointless,
and it’s pretty hard to wire everything properly at those currents anyways. But, please,
if you are using mains power anywhere, be careful, make sure everything is unplugged
before you start working on the wiring and ground your printer frame through the protective
earth rail. I’ve heard from a couple folks that the
silicone heater mats tend to give up after a while, but I haven’t had any problem with
mine so far. And i’ve been torturing it quite a bit.
If you’re wondering what kind of power you need for a certain size, it’s relatively simple:
you need at least about 0.6W for every square centimeter of heated area to get to 120 degrees
for ABS or about 0.2W to get to about 60 degrees for
PLA, but if you want save some time during heat up, you can also go up to 1W per square
centimeter. Just make sure your electronics can handle it. Most electronics are limited
to 10 or 15 amps of output current, which means that they can just about power a Prusa
PCB heater at 12V or something a bit more powerful at 24V. Read the specs for your board
and make sure none of the transistors or connectors burn up when you’re heating it up for the
first time. Now, as far as sheet material for heated beds
goes, again, there are main two choices. You can either use glass and clip that to a heater
PCB, or use aluminum in the same fashion or directly stick a heater mat to it. I prefer
aluminum, it’s cheap, it won’t break, ever, it will distribute the heat from the
heated bed extremely evenly and it will ensure that the surface temperature is exactly what
you want it to be. And you can directly use it with an inductive sensor. For smaller beds,
flatness doesn’t matter as much, but for larger ones, you can get milled, planed aluminum
sheets at almost any size and thickness – this guy for example will end up on top of that
aforementioned 300mm heater mat in the CerbrisReborn. Which i hope I’ll get to build over Christmas,
but it looks like the ball ends for it aren’t going to arrive on time. Anyways, the other
material you can use is glass sheet, and that is pretty much always perfectly flat due to
the way it’s made. Many people use borosilicate glass, which is similar to Pyrex and made
to resist temperature shocks, but i’ve found that regular 3mm window glass works just as
well. Even when I heated up one side of my double heated bed to 120 degrees and left
the other side cold, it never flinched. 2mm is too thin and has a huge risk of breaking
just from the force it sometimes takes to pry a print off.
Also, if you’re planning on using a heater mat instead of a PCB, I’d definitely recommend
aluminum. The heater mats are hand made and can be a bit irregular in their heat output,
which alumium helps smooth out, but also, if you stuck it to a glass sheet and break
that, well, you can probably trash the heater, too.
On top of whatever sheet material you may choose to use, you can use different toppings
as well. But for many plastics, you don’t have to. Many users print directly onto clean,
and this is important, absolutely clean glass, many plastics will directly stick to that.
Then there’s Kapton and PET tape, which are nice for ABS and other higher-temp materials.
And there is the glue section of glue stick, diluted PVA glue and hairspray, each of those
having their own unique properties, and, as always what might work for everybody else
might just not work for you. So there’s definitely some trial and error involved,
but there’s always some way that works out. Most of the surface choices lose their stickyness
when they cool down, so prints are going to be much easier to remove or pop right off
if you wait for the bed to cool down after a print has finished.
One last thing i want to talk about is thermistors in heated beds or # for heated beds. Because
they are always somewhat awkward to place if you want a good reading. If you tape one
to the bottom of the heated bed, the top might end up being much cooler than the spot you’re
actually measuring, if you put it on top of the heated bed, you obviously have the risk
of running into it with your printer’s nozzle. Either way, you should really make sure that
it is well-insulated from the air around it and gets good contact to the spot you’re
trying to measure. Some newer PCBs have a spot in the center to place a thermistor,
which is actually a really decent place to put it. The silicone heaters, on the other
hand, can be configured with a thermistor built-in, but i’ve found that it reports
temperatures that are way too low. Either way, if you have a thermistor in a spot that
isn’t exactly where you need the temperature, i’d at least recommend waiting a bit after
heatup before you start the print, that way the heat has some time to soak through the
entire construction you have on there. Or, if you have an aluminum bed, you can also
use the E3D v6 method and clamp a thermistor into the aluminum plate, that way, you’ll
get exactly the temperature the bed actually is at.
So, i guess that’s got to do it for today, if you have any questions left, please feel
free to leave a comment and i’ll try to answer those. I’ll see you next week, until
then, i wish you all a politically correct happy holidays – i don’t care much about
what you do or don’t do over christmas, but everybody gets a few day off, and that’s
gotta be worth something. Au revoir!


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