Robert's 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 under 2 minutes.
The list of materials needed for this heated bed is quite short:
- 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 (for heating current)
- Wire to connect the thermistor
To form the heating wire in regular loops, you need a bed of nails:
I've used nails with 2.2 mm diameter- 32 nails on each side of the bed of nails. You shouldn't just nail them into the wooden plate but drill 2 mm holes, because you can place the nails with more precision and (more important) more upright. Then you need to cut of the nail's heads and abgrade the cut. This is recommended, because you need to lift the copper-wire up from the bed of nails without harming its isolation.
If you use all 32 loops with the wire from the list above, you'll get a heated bed with app. 1.3 Ohms, consuming 9.23 Aor 110 W at 12 Volts DC. The fewer loops you use, the more power the bed will consume and the hotter it can be driven. The configuration on the picture gives a bed with app.15 A, 180 W at 12V.
Caution! Check the maximum current your electronics allow for the heated bed. RAMPS for example has a strict limit of 11 A for the heated bed. I recommend to use Traumflug's SevenSwitch to drive my heated beds. And you need to be aware, that this construction is designed for 12 V DC. At higher voltages the copper-wire would become too hot and its isolation could melt. You would have to isolate the aluminum plate and use unisolated copper wire. Update: I'm using a 18 A-variant now (using only every second nail to form the heating-wire-loops). The 18A-varaint (220 W) heats up from 21° C to 120° in 3 minutes. I've tested it up to 130° C with no problems and perfect adhesion of ABS on the platform.
To transfer the copper-loops to the aluminum plate, you need to fix their position to each other with Kapton adhesive tape, this by applying the tape only to the wire (under tension) and not to the wooden plate beneath. You can lift the wire from the bed of nails by carefully moving a broach under it, near the nails and tilt it to the left and right a bit. The Kapton preserves the track's distances to each other and you can place them on the aluminum plate.
You need to fix the wire to aluminum plate with the Kapton tape, so the wire can heat the aluminum directly. The adhesive of the tape (usually a silicone adhesive) will withstand the typical heatbed temperatures.
Place the thermistor in the middle of the aluminum plate and fix it with a peace of Kapton tape, better use a thermal conductive adhesive for more accurate measurements.
You can drill threads into the aluminum to fit it to the printer.
Tips and remarks
If the loose ends of the heating wire (the part between the bed and the supplying cable, touch the rescue blanket, it may melt where it touches the wire. That's no problem, because the isolation of the wires stays intact and the small hole in the blanket doesn't affect its function noticeable. The heating wire that has contact to the aluminum doesn't get hotter than the platform itself.
Use a luster terminal to connect the supply cable to the heating wire, not the small connector like in the pictures above. The connector has to withstand over 13 A current and would melt if of insufficient dimension.
The rescue blanket reflects the downward oriented part of the heat radiation from the heating wire up to the aluminum, reducing power consumption and keeping the parts under platform cool without additional heat isolation (saving space and weight).
Using threads within the aluminum allows direct montage of a very simple but effective leveling system:
Tighten the nut under platform to fix the screw in its position. The level can be adjusted by turning the knurled nut.