Recycled Heated Bed

I finally put together an idea that I've had floating around for a while.
My wife had an old heated pad where the fabric had worn through. I took out the plug and element, and saved it, because I though it probably had some nichrome wire in the element.
Fast forward several months, to all this recent talk of headed beds.
I uncovered the element from my 'parts' box, and inspected it - the insulation is all intact, all well covered, no damage and safe. A careful test showed it still warmed up when plugged in.
I grabbed a couple of steel baking trays from Wilkinsons (£1 each) and my kapton tape.

From HeatedBed

I punched a hole in one of the trays, carefully bending the edges and masking them with tape so there were no sharp edges. I could then feed the element through and taped it to the back of the tray in a rough spiral with the kapton tape.

From HeatedBed

The other tray, I covered the base with strips of kapton tape, and placed over the element tray. VERY IMPORTANT: I added an earth wire grounding both of the trays to mains earth (the PSU case).

From HeatedBed

Hey presto, heated bed.

Firing it up, it reached 80C+ in a couple of minutes on 'full'. I haven't run it further than that without mounting it properly first.

Potential problems:

• Using Mains electricity - you need to be *very* careful and earth the case. Check your safety three times.
  
• I don't know what temperature it will reach: it needs to be mounted properly and tested. Temperature control is provided by the original power box - I can have 1, 2, or 3 and it will automatically switch off after 90 mins. (probably not a problem unless I'm doing a long print).
  
• The surfaces of the tins are relatively thin pressed steel. I suspect they're flat enough for 'small' prints (up to makerbot size) - I'll have to see if they're flat/rigid enough for larger objects.

Potential improvements:

• I could fill the thin gap between the element and the two plates with fire cement: it might improve heat conduction and possible help with stiffness/flatness.