<p>I need to do some post processing of my 3D-printed models that includes adding some holes. For each of PLA, ABS, PETG and other 3D-printing materials:</p>

<p>In what ways is drilling a hole in a model made from that material like or unlike drilling wood? Is it worth getting special "plastic drilling bits" that cost tons of money or can I use regular high speed drill bits? Do these plastics have grain that they will split on when drilled into, and if so, what are ways to avoid such splitting? Are higher speeds better, or lower speeds, or should I only use a finger-twirled bit holder?</p>

<p>Are some 3D-printing materials easier to drill than others?</p>

<p>What other methods also work for creating a hole in the different types of plastics?</p>

I wouldn't recommend drilling a hole in a 3D printed part in a traditional sense like with wood. Instead, I would merely ream a 3D printed part.
I've done this quite a bit where I'll print my holes at a slightly smaller than nominal size and use a standard carbide drill to ream the hole.
Things to consider:
Printing the holes smaller than nominal will ensure your hole is not printed larger than nominal
Printing with a higher shell will ensure you can remove the material without exposing the infill
Note that drilling directly into (or thru) an infill area of the part could lead to cracking of the part later, depending on the hole's functionality. In general, a printed hole (even if reamed) will be significantly stronger than one drilled through an infill area.