Well, after a little period of thought and drinking tea, I decided that there will be some bits that I need to buy new in order to recycle the plastic from milk cartons. Although I suspect that I have enough bits lying around the place to build a temperature controller, I have erred on the side of caution (and minimal electric shocks) and bought 2 controllers (the black box with the readouts), two solid state relays (the white/grey boxes on the right) and two temperature sensors (the thing under the solid state relay).
Excitingly, all the instructions are in Mandarin and, as I didn’t learn the Chinese for “Thermocouple Type K input”, I am happy to see the largely-explanatory sticker on the side showing all the connections. I believe there is a translated version on t’interweb somewhere but that won’t stop me looking up some of the characters in my Chinese dictionary just for the fun of it!
I still have to decide on the type of band heater to buy – I am dithering because I am not in my comfort zone when it comes to metalwork and so have yet to come to a conclusion on where to acquire metal piping from and how much tolerance I have on the diameter of the band heaters. Do 35mm diameter band heaters fit OK (with a bit of finagling) on, say, 32mm pipe? Could I use an old steel dog food tin (the tin is steel, not the dog. Or the food.) and heat the plastic in that, thus avoiding lots of welding (which I have yet to learn how to do)?
With so many questions comes the need for tea…