The Combine 

A combine is used to separate the kernels of grain from the straw and chaff. Combines may be either self-propelled or pull type.

The combine has many abilities and operations that it must perform. A combine must pick up swaths of grain. To do this, a special pick-up assembly is used. A conveyor brings the grain in and moves it to a cylinder. A combine must also thresh and separate the grain from the stem. Once the seeds are separated from the straw at the cylinder, they go into a sieve. Then, a combine must also clean and store what has been harvested. Seeds and chaff are cleaned using a sieve. The sieve shakes and stirs them in order to get them clean. You can imagine that it is something like cleaning berries using a colander, shaking and stirring them underwater. Only with grain, air is sometimes used instead of water. The relatively clean seed is later taken to a grain tank. The machine temporarily stores the grain and puts the straw back on the field.

In straight combining, the machine is equipped with its own reel and cutter bar. These tools cut the grain and put it onto a rotating auger. This auger draws the cut grain toward the centre, where it is taken into the machine. 

There are many other special features that a combine might have to help with the complicated process of harvesting. In certain combines, further separation is performed using things such as straw walkers and sieves. Even the most basic combining, however, is a complex process.