For a school project, I'm creating a mechanical arm and I'm thinking about using a 3D printer to create some of the pieces. Obviously, This arm is dynamic, so I wanted to make the pieces as light as possible. Can I drill into polylactic acid without it cracking or losing structural integrity?
Usually 3D printed objects are not 100% infill, you can easily drill PLA, however it can delaminate if you push too hard and go fluffy when hot, producing a rough surface and poor quality finish. 3D Printing is quite cheap and relatively fast, better to design your model with correct holes, the internal structure of the model will then offer better support as the holes will have proper walls.
The problem shouldn’t be cracking or losing structural integrity. The challenge to drilling PLA is its low melting temperature. You can find many internet posts about drilling PLA, but you have to manage the speed of the drill quite closely so as to not overheat the PLA. I have made good holes in PLA with a very slow proces, but I have not tried to tap those holes. Some say it works, but I prefer ABS if I am going to drill and tap. I use ABS almost exclusively now.
From personal experience, drilling into PLA is a bad idea. Print the components after simulating their behaviour in a CAD software