Hay balers are used to harvest hay, and they operate by being powered and pulled by a tractor as the baler's metal teeth gently rake up the hay to a compressor bar that holds the hay in place as the auger feeds the hay into the hay chamber. The chamber contains a plunger that continuously packs the hay down into tight clumps while also cutting the ends of the hay so they have a uniform shape.
This process gives the bales their common size. The chamber uses spring tension to keep collecting and compressing hay until the bale is the right size. Once the bale is the right size, a mechanism then ties the bale together with two strips of wire or twine. This is done through supply pools that wrap the bale while a mechanism called the knotter ties, secures and then cuts off the knot to let the chamber start making a new bale. Once the bale is ready, it is pushed out a bale chute. Some balers have mechanisms that toss the bales into attached areas for finished bales. Balers also come in varying sizes, and their mechanical process can differ. Most balers are constructed out of structural and sheet steel.