A rotary hay rake is a farm machine that gathers cut forage into long, neat rows called windrows so the hay can dry evenly and be picked up by a baler. It is pulled by a tractor and uses spinning rotors with flexible tine arms to sweep hay sideways without chopping it. Good raking improves drying, reduces leaf loss, and helps preserve the feed value of hay.
Understanding the machine helps connect agricultural work with forces, rotation, speed, and energy transfer.
Most rotary rakes are powered by the tractor power takeoff, which transfers rotational energy through shafts and gearboxes to the rake rotors. As the rotor turns, tine arms follow a controlled path so the tines touch the crop, move it inward, and lift away before scraping too hard into the soil. The quality of the windrow depends on tractor speed, rotor speed, rake width, tine height, and crop moisture.
Engineers design these machines to balance gentle crop handling with enough force and motion to move large amounts of hay efficiently.
Key Facts
- Forward travel distance is d = vt, where v is tractor speed and t is time.
- Field capacity can be estimated by Area rate = width x speed, with units converted to acres per hour or hectares per hour.
- Angular speed is omega = 2pi f, where f is rotations per second.
- Tangential tine speed is v = omega r, where r is the distance from the rotor center to the tine tip.
- Power transferred by rotation is P = tau omega, where tau is torque and omega is angular speed.
- A wider rake covers more ground per pass, but proper windrow shape still depends on crop volume, moisture, and rotor adjustment.
Vocabulary
- Rotary hay rake
- A tractor-pulled machine that uses rotating tine arms to gather cut hay into a windrow.
- Windrow
- A long narrow row of cut hay or forage arranged for drying, baling, or pickup.
- Tine
- A flexible metal finger on the rake that contacts and moves the hay.
- Power takeoff
- A rotating shaft on a tractor that supplies mechanical power to attached equipment.
- Angular speed
- The rate at which an object rotates, commonly measured in radians per second or revolutions per minute.
Common Mistakes to Avoid
- Setting the tines too low, which is wrong because the rake can scrape soil into the hay and increase wear on the machine.
- Driving too fast for the crop conditions, which is wrong because hay may scatter, form uneven windrows, or be missed by the tine pattern.
- Confusing rotor speed with tractor ground speed, which is wrong because one describes spinning motion while the other describes forward motion across the field.
- Ignoring crop moisture, which is wrong because dry hay is more likely to lose leaves while wet hay may clump and form heavy windrows.
Practice Questions
- 1 A tractor pulls a rotary rake at 8 km/h for 0.75 h. How far does it travel across the field?
- 2 A rake rotor has a tine tip radius of 1.4 m and spins at 60 rpm. Find the angular speed in rad/s and the approximate tine tip speed in m/s.
- 3 A farmer notices soil mixed into the windrow after raking. Explain two machine adjustments or operating changes that could reduce this problem and why they would help.