How does the grit size of sandpaper affect the grinding effect?

Cutting force and grinding efficiency:
Coarse-grit sandpaper has larger abrasive particles on its surface, so it has a stronger cutting force. That means in the grinding process, it can get rid of surface flaws and raised parts of the material quicker. It's good for rough grinding or taking off a lot of material fast. But because the cutting force is strong, the detail handling might not be that precise.

On the contrary, fine-grit sandpaper has smaller abrasive particles and a relatively weaker cutting force. It's better for fine grinding and polishing, and can make the surface smoother. But because the cutting force is weak, the grinding efficiency will be lower.

Surface roughness:
After grinding with coarse-grit sandpaper, the material surface will have deeper scratches and textures. That's because the big abrasive particles cause more wear on the surface. Sometimes this effect is on purpose. For example, in some artworks, people might want to keep or show off this texture.

Fine-grit sandpaper can make the surface more delicate and smooth. In grinding jobs that need a high surface finish, like polishing metal or grinding before painting a car, fine-grit sandpaper is a must-have.

Applicable materials and scenarios:
Coarse-grit sandpaper is usually good for softer materials like wood and plastic. That's because soft materials are easier to be taken off by big abrasive particles. Besides, when you need to take off a lot of material fast or do the initial grinding, coarse-grit sandpaper is your first choice.

Fine-grit sandpaper is more suitable for harder materials like metal and stone. These materials cause less wear on the abrasive particles. So a finer grit can be used to get the grinding effect you want. At the same time, in situations that need fine grinding and polishing, like making jewelry or making optical instruments, fine-grit sandpaper is also necessary.

Heat generation and clogging:
Coarse-grit sandpaper might make more heat during the grinding process. That's because the cutting force is strong and there's more friction. This might affect the temperature of the material being ground, especially when you're doing dry grinding. Also, because there are bigger gaps between the abrasive particles, the debris is more likely to fall off. That reduces the chance of clogging.

Fine-grit sandpaper makes less heat. That's because the cutting force is weak and there's less friction. But because the gaps between the abrasive particles are smaller, the debris might clog the sandpaper more easily. That makes the grinding efficiency go down. So when you use fine-grit sandpaper, you need to clean or change the sandpaper more often.