Teensy Based IR Blaster via the Adafruit customer support forums… Bbum writes -

When I started this, as can be seen in the image below, the case was two parts that fit together in a semi-complex manner (Actually, the very first version just had a little plastic square that covered the AVR, but nothing else). It was hard to print with any quality and, frankly, the front looked awful. So I simplified it such that the IR LED could stick out a small hole, as seen in the middle. But then it dawned on my that the translucent plastics might just be transparent enough to IR that no hole was needed at all. And sure enough, it just worked! Thus, the design is now even simpler (assuming you have translucent filament).