How Does A Combine Harvester Work?

Oct. 6, 2021

Modern-day combine harvesters are complex machines capable of harvesting large areas quickly and efficiently.

John Deere S780 Combine on display at Farm Progress Show 2021.
Source: Equipment Radar

What Is A Combine Harvester?

The combine harvester is a farm machine that cuts and separates grain. A combine harvester can be used on a variety of crops, including corn, wheat, soybeans, flax, rice, rye, oats, barley, and more. The ability to interchange headers enables combine harvesters to process a wide assortment of grains.

The combine harvester gets its name because it "combines" the job of the header and thresher[1]. Prior to the invention of modern combines, two separate machines were used, and the process took a much longer time. Combine harvesters have played a significant role in increasing overall farm productivity over the past century because farmers can harvest entire fields much faster with fewer workers.

Modern combines are capable of processing about 150 to 200 acres per day on average. Over time technology improvements and larger engines have increased combine performance. The John Deere X9 1100 Combine, one of the most powerful and largest combines on the market today, features a 460-bushel folding grain tank capacity, 690 horsepower engine, speed of up to 25 miles per hour, and an unload rate of up to 5.3 bushels per second. The John Deere X9 1100 can harvest up to 30 acres per hour in wheat and up to 7,200 bushels per hour in corn.

New combines can cost between $300,000 and $500,000, while late-model used combines can cost between $150,000 and $350,000. New and used combine prices change over time based on demand, material costs (steel, copper, etc), and legislative regulations.

Similar to tractors, modern combines feature wheeled and tracked models. Tracks tend to perform better on less stable and uneven surfaces. Typically tracked systems cost more than wheeled systems.

Typically farm equipment buyers look at the combine's separator hours to understand how much the machine has been used. Separator hours indicate the number of hours the machine has been used for threshing, while total hours indicate how many hours the machine has been used. Separator hours are often abbreviated as "sep hours". Engine hours are always greater than separator hours because of unloading and travel time.

Major combine manufacturers today include:

  • John Deere
  • Case IH
  • Challenger
  • Fendt
  • Massey Ferguson
  • Laverda
  • Deutz-Fahr
  • Gleaner

How Does A Combine Harvester Work?

Combine harvesters are huge and complex machines that contain many different moving parts and stages. The combine header cuts and gathers the crops from the field. The crops then enter the belly of the combine and undergo several processes to separate the grain from everything else (stalk, etc). This separation process is where the old saying "separate the wheat from the chaff" originated - the process separates valuable contents (grains) from everything else.

After the separation process has taken place, the grain is moved into the grain tank, and the remaining leftover parts are discharged through the rear of the machine and back into the field. The farmer may then choose to bale the discharge later or let the discharge decompose naturally and provide nourishment to the soil.

Combines can unload their grain tanks while moving, which saves farmers a lot of time. Typically a tractor pulling a grain cart will drive alongside the combine while the combine continues harvesting, and then the combine's grain auger extends over the grain cart and empties the grain tank into the grain cart.

John Deere combine harvester emptying grain tank into John Deere tractor pulling a grain cart


Combine Components

Cutaway diagram of John Deere X9 Combine Harvester

Source: Illustration from Diagram points added by Equipment Radar. Component illustrations below are from John Deere's Cropflow Animation video on YouTube (see citation below).


Combine Header

The combine header cuts and gathers the crops from the field. Most headers have rotating teeth or blades that cut the crop and then a mechanism to move the cut crop to the feederhouse.

Modern headers are typically controlled with hydraulics, which enables them to raise, lower and angle. The ability to move the header is very important because not all fields are flat and even.

Headers are typically crop-specific, and most are detachable. The most common headers include corn headers, draper headers, and knife bar headers.

Most combine headers are measured by their width - wider headers are able to harvest more field at a time. Most combine headers are too wide to travel on open roads - as a result, the combine header must be detached and trailed behind the machine when traveling on a road shared with other vehicles.

The widest combine header in the world is 60 feet wide and is manufactured by MidWest Durus Premium.


Strand Feederhouse

John Deere Combine Harvester Feederhouse

The cut crop is transported up the strand feederhouse (also known as "feeder throat"), by a chain and flight elevator. The feederhouse lifts and deposits cut crops from the ground level into the belly of the combine to begin processing.


Variable Stream Rotor

John Deere Combine Harvester 3 Stage Separation

The stream rotator spins at a high rate and begins the threshing and separating of the crop. The function of the stream rotator is similar to a household blender. The rotator is designed to break down the stalk and large components while protecting the grains.


Threshing & Separation

Most of the lower belly of the combine is dedicated to separating the grain from everything else. The basic mechanical function of the separation is similar to panning for gold - mixed contents are moved over a porous surface while it shakes. The large materials (stalks, leaves, roots, etc) then separate from smaller materials. Smaller materials such as grains, fine particles and dust fall down into a collection area.

The combine blows fast-moving air over the collection area to remove very lightweight items such as dust and other fine particles. The remaining material is mostly grains.

John Deere Combine Harvester Internal Separation
John Deere Combine Harvester Pan and Separator
John Deere Combine Harvester Pan and Separator

Tailings Return

Trailings are recirculated through the combine to go through the process again. Materials often need to circulate through the threshing and separation process multiple times before grains fully separate.


Grain Tank

Grains are then lifted from the bottom of the combine and into the grain tank using a grain elevator.

John Deere Combine Harvester Grain Elevator
John Deere Combine Harvester Grain Tank Storage

Grain Auger

The grain auger (the large arm that swings out) moves contents stored in the grain tank into the grain cart. Typically the grain cart is pulled by a tractor moving alongside the combine while it continues harvesting.


Rear Discharge

Waste products (stalks, etc) are discharged through the rear of the combine and returned to the field. The discharge is typically collected by a baler at a later time.

John Deere Combine Harvester Rear Discharge
John Deere Combine Harvester Rear Discharge Beater
John Deere Combine Harvester Rear View

History Of The Combine

The first combine harvester, which was capable of reaping, threshing and winnowing cereal grain, was invented by Hiram Moore in 1835. Since then, the combine harvester has had a long and interesting history of advancements and improvements. Despite significant improvements in productivity and design, the basic operation of the combine harvester has remained almost the same since it was invented[2].

The invention of the McCormick reaper by Cyrus Hall McCormick in 1831 was a technology breakthrough that was instrumental to the creation of the early combine harvesters. The McCormick reaper was a horse-drawn machine that cut grain stalks in a more efficient way. Cyrus McCormick later became known as the "father of agriculture"[3] and served as the President of McCormick Harvesting Machine Company (later International Harvester, and Case IH).

The combine harvester because more prevalent in the 1930s when farmers began to attach them to tractors. In the 1940s the self-propelled model was created and could cut areas wider areas. The self-propelled models started out with a manual transmission and evolved in the 1950s to a spring and hydropic type system to allow the machine to operate at four different speeds. This eventually evolved into today's high-performance hydrostatic drive systems.

Early versions of the combine harvester required more than 12 horses to provide power. Horses were gradually replaced with steam engines that used hay. Eventually, most combine harvesters models adopted diesel or gasoline engines.

One of the most important technology developments for combine harvesters was the integration of a continuously variable transmission (CVT). CVTs enable the combine to vary its ground speed while maintaining a constant engine and threshing speed.

John Deere Combine Harvester Number 55

John Deere Combine Harvester Number 55
John Deere Combine Harvester Number 55

Minneapolis-Moline Combine Harvester

Minneapolis Moline Combine Harvester
Minneapolis Moline Combine Harvester Header


John Deere | S700 Complete Cropflow Animation

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