3D Print-head and Heated Pad?

Hi,

I am a retired Mechanical Engineer and along with a lot of other machines in my garage, I have a commercial ($30,000 in 1998) CNC milling machine with 30" x 20" x 20" envelope. It has 40" per min Feed and 100" per min Rapid with 0.0002" repeatablity. Supper accurate and runs standard GCode.

I don't use it much anymore and was thinking of adding some 3D printing parts to it. I am looking for advice on print heads, controllers and heated pads. The heated pad does not need to be huge to play with this set up, so 6" x 6" or 8" x 8" would be fine. Being retired, I no longer have a lot of money to spend, so I want to get good equipment for a reasonable price.

I have seen the Gnexlab controller but need advice on Thermocouple / Thermistor. I know the difference between them, but need to understand which is used where and why.

Who makes a good complete head at a reasonable price?

As an Engineer, understanding is way more important than just buying stuff on someone's say so. :)

Thanks

Harry