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:
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!
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.