Unfortunately, I'm not sure our idea for the thermistor will work out. I didn't know how the arduino was measuring resistance until I did a little research, and with my limited experience in electrical engineering (nearly none), it didn't occur to me that the amount of resistance we were getting out of the thermistor trace on the plate would be difficult to work with. The arduino with RAMPS is doing a voltage comparison by creating a divider on a 5V circuit with a 4.7k resistor on one side and the thermistor on the other. The typical thermistor is 100k and has a really huge swing in resistance which works great with the 10 bit resolution of the analog inputs. But my thermistor only vaies from 230 to 290 Ohms over the temperature range I'm interested in which isn't enough. I could swap out the 4.7k resistor for something close to the value of the thermistor, but I'd rather not mess with the board, and I'm not sure what affect the increased current (~50mW by my calculations) would have on the arduino board. So I think I'll just tape a 100k unit to the top of the board for now.
I clearly need to blog more often so I don't feel like I'm writing a novella every time I decide to post. Next up, dealing with mechanical issues and some ideas for vertical X-axis design.