Magnet Wire Heated Bed

Hi I have heard from many people that using magnet wire for a heated bed heating element is a no go. But I have to challenge the nay sayers to this.

I found an interesting article published in 1987 found here http://deepblue.lib.umich.edu/bitstream/handle/2027.42/70951/RSINAK-58-10-1964-1.pdf?sequence=2&isAllowed=y that describe magnet wire as a heating element insulated in polyimide.

Most know this but I will say it incase people are not aware that polyimide is kapton tape.

After some testing with different lengths and have some wire burn out on me. I have built a working model, I will post photos here this evening. Basically it is about 5 ft of 24 awg(I think) magnet wire zig zagged on the sticky side of a large sheet of Kapton Tape (8"x10") with a slightly smaller sheet of Kapton (6.5"x8.5") over it attached sticky side to sticky side with the smaller sheet centered on the larger sheet covering all of the magnet wire and the 2 ends of the leads coming off the magnet wire. I attached the thermistor to the bed using Kapton tape then I used ~.6" border of the sticky side of the larger kapton sheet that is still exposed to attach it to the under side of the aluminum bed. I use an aluminum bed and that disperses the heat relatively evenly and gets up to around 60C in 10 minutes.

I will continue to test this but it might be an option where nichrome may not be available.

I am sure it is possible to use fine enamelled copper wire to make a bed heater as you describe. However, stick-on Kapton or silicone heaters are not expensive. This company [www.aliexpress.com] will make a stick-on silicone heater to your own voltage, power and size specifications at low cost. I had them make me a 230V 350W heater for my delta printer.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

I know there are a lot of options but I am trying to think of alternatives for people that may not be able to order parts online easily or are on limited budgets.

Yeah total cost was less than $5 for an 8x10 heater that runs directly off of the 12v heatbed terminal on the printrboard rev d.

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@Archaejon - do you have an pics?

Like you, I have thought about using magnet wire, but I think the big issue is lack of wire surface area and local wire surface temperature. I suspect it is much higher than the aluminum plate. Also there are high temp grades of insulation. Be interesting to get some estimates of the actual wire temp by doing a 4-wire resistance measurement of the wire under load. Kapton will start to degrade at high temps.

@ dc42 - good info. I've bookmarked your link. Certainly good arguments. But when you buy an off the shelf pad, you are making the assumption that it was correctly designed. How do you know? This was an eye opening study:

[www.sd3d.com]

Seems like being able to make your own heater lets you tune the design. Many beds cool off towards the edges, so there's probably an opportunity to tweak power densities for more uniform heating.

Many of the designs being used today employ a heat spreader. But I think there are serious issues controlling the air gaps between the spreader and the glass print surface. Random warping of the heat spreader means air gaps and resulting the temperature gradients change over time. There is also the extra mass of the heat spreader for machines that have beds that move in Y.

Expanding on Archaejon's wire design, what about using 1/8" sticky back copper tape? like: [www.amazon.com]
Applied directly to the back of the glass with 1/8" conductor gaps. I ran some 2D thermal sims a while back with 6mm trace/gap and 3mm glass that showed about a 3C gradient at the print surface of the glass because of the conductor gaps. With 1/8" conductor/gaps, the gradients should be much smaller.

While it would be nice to just pop the glass off the machine for cleaning and part removal, having the DIY heater come with it and having to disconnect some connectors is not the end of the world.

The copper strip adhesive is listed as acrylic (something) with temp range to 120C(?). I think there would be an opportunity to cover and insulate the copper conductors with some layers of Kapton. Might be interesting to add some backing layers of aluminized mylar thermal rescue blanket or cork. Anyone know of an adhesive that could bond cork to kapton?

Glass is a thermal insulator, so of course it's going to cause irrregular surface temperature. The solution is to use use a flat piece of aluminum such as cast tooling plate and print on its surface (with a layer of PEI, Kapton, or PET tape). If you MUST use a removeable plate for printing, clamp a thin plate of aluminum to the tooling plate and apply the kapton to the removeable plate.

Why would you use magnet wire when nichrome wire is cheap, readily available, and has a more predictable resistance?

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

use sicilone embedded nicrome wire the one they use in blankets. i made beds for both my printers this way ( total cost of wire 2 dollars ) , and run them on 220v ac via a ssr. Ihe wire is attached to the under side of aluminum 3mm plate and insulated with 10mm cork. This is the cheapest solution if you are looking to save money.

Silicone pads are the best way around. ( use 220/110v ones, they are much faster and you dont need a huge power supply )

I remember seeing someone on a forum make silicone pads by embedding nichrome wire between silicon liquid gasket .