RepRap Ormerod 2 quick-set dual-nozzle dc42 sensor board PLA/ABS switchable heat sink enclosure and nozzle-cooling ducts

Hot end heat sink enclosure and ducts for Ormerod 2 quick-set dual-nozzle setup with [dc42's](http://www.thingiverse.com/dc42/about) improved [differential infrared height sensor board](https://miscsolutions.wordpress.com/ormerod-hot-end-board-v2/).

A removable shutter allows airflow to be directed at the nozzles (for PLA) or upward (for ABS). Or both at a reduced rate (shutter removed completely).

You will need to rotate the heatsink 90 degrees so the fins are vertical. A third hole will