Some closeup pictures for your comments and interest. Here are some recent wiring additions to add push button controls (start and stop initiation), led indications (preheat, soak, reflow, cool) and Thermocouple input. Using a CAT5 jack for connection to human interface control board (buttons and leds).
lower right corner is LM7805 attached to enclosure feeds arduino power and power to control box led indication, walwart for 12v relay power
Adafruit T/C board standing on end so as not to obstruct other digital I/O points. Relays in foreground.
Cat5 cable for connection to external pushbutton and led indication control board. Ribbon cable for connection to relay board under Arduino.UNO are 4n35 optocouplers for relay interface.
Youtube Channel "Hamradio2008"