3D Printer Heated Bed

Intro: 3D Printer Heated Bed

I've tried several kinds of heated beds over the last months. But I
was wondering, if there wasn't a far simpler, more efficient and even cheaper way to build one. So I've developed a heated bed, based on an aluminum plate, heated by isolated copper-wire. No etching is required, no exotic machinery and only materials any RepRapper should easily be able to buy.

In its 13 A-Version at 12 V the bed heats up from 21° C to 110° C within 6 minutes. You can drive the bed with 18A (e.g. with SevenSwitch; 216 Watt), which gets you to 110° C in app. 2 minutes.

The list of materials needed for this heated bed is quite short:

• Bed of nails, made form wood and 64 nails with 2.2mm diameter
• Aluminum plate, 220 mm x 220 mm x 3 mm
• Kapton adhesive tape, slim (e.g. 20 mm)
• Rescue-blanket (gold on one side, silver on the other)
• Thermistor (e.g. EPCOS B5781S104F40)
• Copper wire, isolated, 0.56 mm diameter (0.6 mm with isolation)
• 1.5 mm² wire (has to withstand the heating current)
• Wire to connect the thermistor

STEP 1: Form the Heating Wire With a Bed of Nails.

Make a bed of nails and place 32 nails in equal distances on two sides. You may add nails in the middle of the first and the last row too.

Cut off the heads of the nails.

Stretch the copper wire using the nails like shown in the picture to form a regular pattern. The less windings you make, the more powerful the heated bed will become, consuming more power though. Using only every second nail on each side will result in an 18A heated bed (I love it!).

Remember that you need a powerful electronic to drive an 18A bed (e.g. SevenSwitch). RAMPS1.4 only drives up to 11A and you shouldn't push it to it's maximum abilities. A cheap SevenSwitch is a good replacement and works with 18A beds like charm.

STEP 2: Fix the Wire Distances

Use some Kapton tape to fix the wire in its actual form. The tape should only adhere to the wire, not to the bed of nails below, because you'll have to lift the wire up in the next step.

STEP 3: Lift the Wirefrom the Bed of Nails

Because you've cutted the heads off the nails earlier you can now lift the wire from the bed of nails. The Kapton tape keeps the form you gave to the wire.

STEP 4: Place Wire Below the Platform

For my builds I drill 3 3.5mm holes into the aluminum (two on egdes on one side and one on the opposite side in the middle, because I use three points for leveling the bed). Prepare your platform in your own purposes and requirements.

3mm Aluminum are just enough to give a plain and stable building platform. And you don't need anything else for printing on it. Just spray some hairspray on the platform before you print. That's all. And after printing let the platform cool down and your print will come right off the platform by itself (because aluminum has a very different thermal expansion coefficient to plastic). And printing at 110° C and above prevents warping just perfectly. So forget about glass, clamps and expensive coatings.

Fix the wire to the bottom side of the aluminum platform, using the Kapton tape on the wire. You can add some tape if you seem to need it. Most if the isolated copper wire should touch the aluminum.

You don't have to be very accurate here, because the aluminum will spread the heat from the wire to the surface very evenly.

STEP 5: Uninsulate the Wire-ends

The isolated wire needs to get uninsulated so you can connect it to the supply cable.

STEP 6: Place Thermistor Under the Platform

Place thermistor in the center of the platform between the wiring. You should use a thermal conductive adhesive or Kapton tape and thermal conductive paste for that.

STEP 7: Check Resistance

You should measure the resistance of the heating wire, to ensure you didn't short-circuit it.

Be aware that standard meters are not very accurate at low resistances like we use it. Well, it's not that important know the exact resistance, as long as you didn't left out more than one nail per row to form the wiring.

SevenSwitch can drive far more than 18A at 12V, but you need an adequate power supply!

STEP 8: Add Thermal Cover

After connecting the power-cables to the heating wire (don't solder, but crimp it!) you can cover the bottom side of your new heated bed with a rescue blanket.#

The silver side should face to the aluminum, the gold side off the platform. The silver side is electrical insulating, in case some of the wire insulation fails in operation (remember, we're operating at over 110° C).

The silver side reflects the heat of the wire and from the platform back to the aluminum, resulting in less power consumption, faster heating up and, more important, leaving anything below the heated bed cool without additional thermal isolation!

Tipp:

Some of the rescue-blanket may melt on your first attempts. That's no problem at all. You can leave the resulting holes as they are, except the construction underneath become too warm. Then you can just place a patch of rescue blanket with some Kapton tape to fix the holes or just replace the whole blanket.

I love this solution. It's very inexpensive and easy to make. Even the Thermistor is a very cheap one (only has to work slightly above 110°C though).

And it's a lightweight solution, so if your printer moves the bed, this solution is good to your bearings and motors on the long run.

Comments

[fewtheG]

Would using screws instead of nails work? this may seem like a dumb question.
however I find screws easier to place evenly and they make for a nice Grove for the copper wire to "sit" in..

[RobertKuhlmann]

Hi fewtheG,

screws instead of nails will not work, because you'll not get the heating wire lifted up from the bed of nails. It will stuck on the thread if the screws.

So, please, use nails and cut their heads of after hammering them into the bed of nails. To get even spaces between the nails you may print a mask for the nail-positions and drill a small hole for every nail.

But you don't have to be 100% accurate with that, because little differences in the spaces between the nails don't matter, because the aluminum delivers the heat very evenly from the heating wire to its surface. As long as there are no short-circuits between loops of the wire, anything will work just fine.

The better the contact of the wire to the aluminum, the more effective the heating bed will operate.

[bgrupczy]

Screws would work better IMO. Just UNSCREW them after wrapping the wire. Don't drive them deep into the wood of course. And care taken to not break the insulation. But that would be the same as for the nails.

[lathe_makeatio]

Nice and simple solution!
The only thing I wonder if the coating of the wire will stand a long time good at 110 C and doesn't become hard an peels apart. I just remembered overloaded transformers which coils where overheating. ;-)
My solution for power supply wires are those soft measuring wires that sold for laboratory power supplies or measure units.

[RobertKuhlmann]

Over the years you might have to replace the wire - maybe. So don't through your bed of nails away and you can replace the wiring anytime. (making the bed of nails costs the most time here, but it will let you make many heated beds though)

The materials are so inexpensive, that you can e.g. make two beds, so if one fails (what I didn't observe until today, printing often at 130°C) you have a replacement.

And you're right. Good power supply cables are important, as 18A are a heavy load for the cables.

[RobertKuhlmann]

Whuaaahhh. It should read "don't THROW your bed of nails away", of course.

[RobertKuhlmann]

Just one comment on wire-temperatures, isolation-failure and short-circuits:

The
risk of short-circuits because of isolation failure is very low,
because the wire only becomes hot where not in direct contact to the
aluminum (where it gets cooled, because its heat is conducted into the
aluminum). So the isolation of the heating wire will, if ever, most
likely fail where it doesn't matter.

[autoCorekt]

Can this be scaled up to work on a larger bed, such a 450×450?

[RobertKuhlmann]

Yes. You can either use the same wire length and less density per square inch (but that reduces maximum heat and speed), or you power several sections with several driving circuits.

[mdlafond]

How would this be attached to the bed? Thanks

[RobertKuhlmann]

Hi,

I'm not sure if I got our question right.

How you attach the heated bed to the printer depends on the construction of the printer, of course.

In my project I attached it to a RepRap Morgan, i.o.w. the heated bed was mounted above an aluminum platform. But meanwhile I've also attached it to a RepRap Prusa Mendel (wooden base) successfully.

Or maybe I didn't get your question?

Greeting Robert

[mdlafond]

Thanks, Robert.

[Celsod3]

How can I convert it to a 24V + 20A system? Thick wires?

[RobertKuhlmann]

If you mean to make it more powerful for the same dimensions, you may indeed double the voltage (same wires). The problem will be, that the wires would get hotter. If the aluminum is not able to dissipate the heat fast enough, the insulation will fail even in places where the wire touches the aluminum, leading to short circuit and fail of the whole thing.

You can, instead, double the wire length, in other words put the wires closer together under the same bed. Double length of the wire with the same diameter doubles the overall resistance and can therefore take double the voltage but still with the same amperage.
Since you now would have more heated wire for the same area the heating power will be nearly doubled, while dealing with the same temperatures.

Greetings
Robert

[Celsod3]

Mr. Robert, thank you for your very thorough and simple explanation so I could get the point. Thank you very much.

And as we are at it, what do you think about this method of making a heatbed?

https://www.youtube.com/watch?v=EELMtH_e2ow&list=PLUED9xxQ0Y8FZWhZ2hO_mZR6NYtwMsfjc

He applies a layer of enamel before installing the wire, but then his results aren't as good as yours. My opinion (as a layman) is that he should have given the first layer of enamel (just at the end).

However this is just a hunch... I think a combination of both techniques would deliver a pretty and efficient heated bed... but I'm not an expert, I would appreciate your take on this,

Cheers

Celso de Sá.

[RobertKuhlmann]

Hi Celso,


thanks for the compliments.
I know the videos of that guy and appreciate him very much.
Concerning his heated bed you are right. It is less efficient. Reason is the relatively thick coating between the conductive ink and the aluminum. This leads to heat losses to the downward side of the bed and there is no reflector to bring that heat radiation back to the bed.


But what I don't like on his solution the most is the effort in material and time. The spray paint, the conductive ink and the copper foil. I designed my solution the way it is, because it is a cheap as it can get and very easy to make. And it is, as you not already, very efficient and fast.


And it works very well with 12V.


Have a nice day.

[Celsod3]

Thank you very much for your insight, I'll take all this into account - and yes, your solution is the most efficient AND cost effective: Thumbs up!

[swannjie]

Hi, i just bought three components online, what else do I need to turn on and off the heat bed? My 3d printer does not come with any heating bed and i want to move the heat bed anywhere I want independant of the printer. Would you know what else I need and how to complete the set up?

[richfiddler11]

In theory, you could power a heater like this this with AC line voltage. You'd need a power resistor to limit the current (and/or a different type of wire with higher resistance) and some type of thermostat. Electric blankets/heating pads do this with very little circuitry. Naturally, insulation would be come a much bigger concern!

Here's a link to an electric blanket circuit from a US patent: https://patentimages.storage.googleapis.com/pages/...

[dscott22099us]

Patents tend to be more of a proof of concept. Electric blankets don't get much hotter than 100 degrees. The external temp of the human body is not much over ambient temperature, so a heating blanket need only make it feel warmer than the skin already is. It also uses the blankets insulation to capture the heat from the body, reducing the need for heat from the blanket. Electric blankets came about from the affluent being too lazy to generate the heat naturally.
I come from automotive background where high current devices required large wire and heavy contacts. You could run isolated copper wire in multiple loops across the surface of an aluminum plate, held on with that tape that withstands heat, making sure that you keep the resistance around 0.7 to 0.8 ohms. If you use the two terminals on your motherboard that are usually used to power a bed heater, and connect one to the ground terminal (pin 86 on standard 4 pin relay), and the positive terminal to the signal in terminal (pin 85), then connect the 12v positive wire from power supply to pin 30, then use pin 87 to power the heated bed. That will off load the high current load from the tiny three legged mosfet transistor on the motherboard. Running more than 10 amps through something that small is just asking for trouble. It is much more stable to simply offload that function to something designed to handle it. So much more stable that writing this out just convinced me that this is the solution to my recent experience with toasting that transistor.