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:
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?
Are some 3D-printing materials easier to drill than others?
What other methods also work for creating a hole in the different types of plastics?
Drilling is indeed possible, but as stated in previous answers you should preferably do this along the vertical from the print bed for maximum strength, and if possible use an undersized hole as a starting point/guide. Drilling horizontally may cause the layers to separate but if you clamp down in the z-direction you're much more likely to succeed. It's likely to start cracking if even a relatively small torque is applied (one layer with bad adhesion is enough to make it surprisingly weak). If you still need to apply torque from the horizontal consider reinforcing the structure in the z-direction or splitting your print and gluing/fusing the pieces together to get some strength in both directions. Two holes of decent strength (one along the vertical and one along the horizontal) can also be achieved by adding vertical holes and bolt the layers together. When drilling take care not to apply too much force and make sure the excess doesn't get stuck in the drill bit. Any drill bit should work but I find that wood ones have a slight higher tendency to make the bit jam.