Since the last post I've had a look into types of plastics and ways of heating and determining the temperature. My endevours to find how to heat the extruder came back with some great answers. I first had a look at how the RepRap worked and found they used a thermistor to heat the filament and from what I can determine they either don't monitor the temperature after setting it or they do this through the same thermistor (example). This thermistor tended to be quite large and powerful. I had a look at these on wikipedia and it said they could normally only go up to around 130˚ Celsius. This I was intrigued at how the RepRap got them to cope with the 230+ temperature but I kept looking. I eventually found resistance themometers but once checking the price found they were a tad too expensive (starting from $10 a piece). I kept looking and decided to look on element14 (Farnell) and found there were in fact thermistors that could cope with 300 degrees so I'll stick with that I reckon. So that thermistor will be used for measuring temperature and then I'll use another component to heat the extruder. I have two ways currently of doing this, using the same method as RepRap using a thermistor or using nichrome resistance wire which is cheap and the same stuff that toasters use. This would allow it to be placed inside the hot end if I wanted and would be far neater compared to a resistor that sticks out. Its also very easy to get hold of (for example in Australia you can get it from Jaycar). For setting the temperature of the elements, I will have to use PWM or similar. "Or similar" because PWM tends to be in kilohertz where as for heating elements it seems to be a number of seconds before you switch states. Before I forget the reason I want a separate temperature sensor is because I would prefer accuracy, specially for measuring chocolate temperatures where only a few degrees can change the state/phase of the chocolate. The two plastics below (ABS and PLA) have quite large ranges of temperatures it seems being 225-250 and 190-230 respectively.
So the two plastics I was checking out are ABS and PLA. ABS is the type of plastic that is used for LEGO! and PLA can be used for disposable tableware for example. There's two sources I used which are this forum topic and this video. The video starts of kind of weirdly as I think its actually a skype call. Its between someone who is interested in 3D printers and the maker or something of one of the 3D printer companies. From these two sources I decided I would most likely start off with PLA as it has no fumes and then once I have PLA working nicely I'll start using ABS but move the printer from inside to the workshop/shed. Just for reference for me, the cheapest place I could find in Australia for ABS and PLA filaments was ozreprap.com.
I don't know how I found this but another source of plastic which would be a great idea is old plastic bottles and food containers. I found out from a kickstarter project that these can easily be melted and then formed into plastic filaments. Pretty cool idea and would save lots of money. You could also get different colours such as green and blue from sprite bottles. I was also wondering if it was possible to put powder die in and colour the plastic too which could potentially make coloured see through plastic of lots of different colours, could even make swirls of colours. I wouldn't start designing anything until after I've made the printer though.
Other things I've thought of are that I can use a gear style pump for moving chocolate around and a heated tube for moving it round. The heated tube could either be bought or made with nichrome resistance wire coiled round it. I'm not sure which of these is cheaper or most effective (and safe). Another item which I forgot to add above was that one of the wiki pages on RepRap said that for faster printing, the hot end should be longer.
One last thing that's electrical based is that I think I will put two hex switches (switches with 16 positions, outputted in binary, ie 4 pins) that can be used to set the I2C addresses of the slave controllers without reprogramming, so I can quick change them if they break. I'll also have a jumper on the slave control boards so I can swap the default directions.
Think thats everything, I really had to push myself to make this post as I've been too tired in the evenings after study and in the mornings I'm most ready and roaring to go and study. I have been giving myself the nights to relax so that is why I have had time to research though.
