Categories: Articles, MechanisationPublished On: 19th July 2021

The operation and application of medium and big square balers Part 1: Bale sizes, designs and component functions

By 5 min read


by GJ Stoltz (Reg Eng Tech)

This month we start with our series on balers with an in-depth look at square balers and their benefits for feed production. Stationary balers were well-designed and popular with farmers many years ago. By the 1930s, a few companies had converted stationary balers into mobile square balers by adding a pick-up attachment, but the major development came when automatic twine-tie and wire-tie mechanisms were developed.

Baling is a packaging operation and baling is better and more effective than any other hay packaging method. Loose hay takes twice as much storage space as baled hay and baled hay makes long-distance transportation more feasible.

Square balers are classified by the power source required, the size of the bale produced, end the method of binding the bales – twine-tie or wire-tie. The tractor must be powerful enough to maintain a constant engine speed during baling, and have enough forward speeds to match crop conditions.

This article series discusses the operational features of the medium square as well as the big square baler.

Modern square balers have the flywheel mounted on the PTO drive shaft with a safety slip clutch mounted in front of the flywheel. The flywheel absorbs shocks during the baling process.

Bale sizes

Hay bales are produced in four sizes, namely:

  • 355 x 457 x 914 mm, and weighs approximately 22 kg
  • 406 x 457 x 914 mm, and weighs approximately 32 kg
  • 406 x 610 x 1 219 mm, and weighs approximately 57 kg
  • 1 220 x 1 220 x 2 440 mm, and weighs approximately 908 kg

The last bale size is a bale that is produced by a big square baler, also called a big pack baler. The operational features of this baler will be discussed at a later stage. (See Figures 1 and 2.)

The medium square baler

List of primary components:

Figure 3: Front view of a square baler
  • Pick-up
  • Compressors
  • Tongue
  • PTO drive shaft
  • Pick-up lift crank
  • Plunger inside the bale chamber
  • Feeder teeth
  • Auger
Figure 4: Rear view of a square baler
  • Flywheel
  • Needles
  • Bale chute
  • Tension bars
  • Tension cranks
  • Bale chamber
  • Bale measuring wheel
  • Wire twister or twine knotter

Latest designs

Nowadays there are a wide choice of square balers available that feature a straight-forward and rugged drive layout, a pick-up that rakes up the crop from the field and form bales that are densely packed and stored for long periods (see Figure 5).

Figure 5: The latest design in some of the medium square balers.

The following primary components are shown in Figure 5:

  • 1. Adjustable drawbar to ensure correct hitching on all tractors.
  • 2. Extended drawbar with a two-section PTO shaft.
  • 3. Adjustable support jack for easy hitching.
  • 4. Slip clutch on the PTO shaft, and a shear bolt on the flywheel to protect the baler. The built-in free-wheel mechanism protects the tractor’s transmission.
  • 5. A heavy flywheel ensures smooth transmission and maximum power transfer.
  • 6. Hypoid gearbox for smooth drive and resistance to wear.
  • 7. Heavy duty plunger runs on sealed bearings for minimal maintenance.
  • 8. Shaft drive for feeders and knotters.
  • 9. Pick-up height adjuster via a cord from the tractor seat, but a hydraulic height adjuster is optionally available.
  • 10. Pick-up drum with closely spaced pick-up tines.
  • 11. A short crop baffle plate to direct the crop to the pick-up tines.
  • 12. Rotary feed rakes to convey the crop positively to the bale chamber.
  • 13. Device whereby the rotary feed rake can be adjusted to give an even feed under all conditions.
  • 14. A shear bolt to protect the rotary feed rake.
  • 15. Shock absorber to protect the rotary feed rake from peak loadings.
  • 16. An angled stationary knife to cut the crop.
  • 17. Knotters or wire twisters at the back of the baler.

Component functions (see Figure 3 and 4).


The pick-up lifts hay from the windrow and carries it to the auger or feed rake.

Hay compressors on the pick-up hold the hay down for uniform feeding and prevent strong winds from blowing hay out of the pick-up (see Figures 6, 7 and 8).

Figure 6: The compressors hold the hay down for uniform feeding.
Figure 7: The windrow must have the correct width to suit the width of the pick-up.
Figure 8: Pick-up height adjusting is done via a cord from the tractor seat.

Auger (feed rake):

An auger or feed rake delivers the hay to the edge of the bale chamber. The feed rake then delivers the hay into the baling chamber and the feeding teeth of the feed rake are timed to enter the baling chamber when the plunger is retracted (see Figures 9, 10, 11, 12 and 13).

Figure 9: An auger or a feed rake delivers the hay to the bale chamber.
Figure 12: The stroke of the feeder teeth can be adjusted by choosing the correct hole for the pivot pin.
Figure 13: The feeder teeth must be timed in such a way that they never touch the plunger.

Next month we shall discuss the plunger, hay dogs, bale chamber, bale measuring wheel, needles and knotter. Visit for
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