I ordered a small batch of 16 cm diameter round heating pads from China,

I ordered a small batch of 16 cm diameter round heating pads from China, specifically for use in @Richard_Horne 's 3DR delta printers. I have added one to my printer and it works perfectly. They are 12V 50W heaters with a 1 metre power lead designed to reach the electronics under the top cover. I used a stack of corrugated cardboard circles as insulation (probably far more than necessary, but I didn’t have any other M3 bolts of the right length available) and placed a standard thermistor directly under the pad. I found that I could squeeze a thermistor lead and the power lead into one of the channels in the aluminium extrusion.
If anyone is interested in having one of these heaters, I have put the others up for sale in my eMaker shop in the electronics section.

50W doesn’t sound like much

True, but since my 3DR is all made from PLA I wasn’t planning to take the bed up to ABS temperatures. I just wanted more reliable adhesion than printing PLA on cold glass.

I don’t have any adhesion problems with tape + a bit of rubbing alcohol. 3DR is a fun little printer. Are you sure you have that fan mounted right ?

How even is the heat without an aluminium heat spreader? Most people with heatpads tend to use one. Do you worry about that cardboard? Looks like good kindling to me! I wrapped mine in tin foil (not sure if that helps reduce its flammability, but it at least looks less flammable to me)

@Shachar_Weis - the fan is pointing up at the fins of the hot end, as recommended for J-heads.

@Liam_Jackson - good point, although I am only warming the glass to 50C so the cardboard is unlikely to spontaneously combust. My glass disc is 4 mm thick which evens out the heat pretty well. I used an IR thermometer to check the surface and there was very little variation across the bed.

Hey Richard,

Are you planning on getting any more of these? I’m quite interested in getting a couple.

Hi Bob, no sorry. I just ordered 5 from AliRubber in China. I sold the rest pretty quickly but that covered all my costs so basically mine was free.