A tractor’s power takeoff shaft turns at a standard 540 or 1000 RPM and can drive mills, saws, pumps, generators, balers, compressors and augers, so chock the tractor, run it outdoors and match each implement to the shaft speed marked on it. Shut the engine off before touching any guard, belt or shaft, because a turning PTO shaft pulls in clothing and limbs in an instant.
The PTO turns a tractor engine into a portable power plant, and the same shaft can drive a stationary belt to run machinery that has no engine of its own.
The Standard Shaft Speed Is What Lets One Tractor Run Many Machines
The parent article gives the PTO shaft speed as a standardised 540 or 1000 RPM. Applications (parent article):
- grain mills (Grain Mill Design)
- sawmills, circular saw or bandsaw (Sawmill Design)
- water pumps
- generators (PTO generators are common farm equipment)
- hay balers, feed grinders and threshers
- air compressors
- post-hole augers
A running tractor with fuel is an industrial power plant, and tractors and their fuel are strategic assets (parent article).
What You Need
- A tractor with a working PTO, fuel, and a PTO shaft with its guard.
- An implement rated for the PTO speed, or a belt pulley and belt to a stationary machine.
- Wheel chocks, a firm level site, and a belt guard.
- Pulleys, V-belts and a straightedge for alignment.
- Gloves, eye and hearing protection.
Method: Site, Align, Guard, Run
Step 1: Site the tractor outdoors on firm level ground. Set the brake, put it in neutral or park as appropriate and chock the wheels.
Step 2: Check the speed. Read the implement’s rating: 540 or 1000 RPM. A shaft that runs faster than the implement is rated for can destroy it.
Step 3: Connect. For a direct PTO implement, fit the shaft and its guard; for a belt drive, fit a belt pulley to the PTO and run a belt to the driven machine’s pulley, aligned with a straightedge so the belt runs true.
Step 4: Set belt tension so the belt does not slip but is not tight enough to overload bearings.
Step 5: Guard. Cover the belt and pulleys.
Step 6: Run up slowly, from idle to working speed, watching and listening.
Step 7: Shut down to adjust. Stop the engine, wait for the shaft to stop turning, then work on guards, belts and feed.
Worked Example
A driven machine needs a different speed than the PTO supplies, so the pulleys must differ. The driven pulley diameter equals the drive pulley diameter times drive speed divided by driven speed. Suppose, as an example, a machine needs 3,000 RPM and a 400 mm pulley sits on a 540 RPM PTO. The driven pulley is 400 × 540 ÷ 3,000 = 72 mm. Check the ratio the other way: 400 ÷ 72 = 5.6, and 540 × 5.6 = about 3,000 RPM. Belt-speed and bearing limits still apply; read your machine’s rating.
Common Mistakes
- Using the wrong shaft speed. The implement runs too fast or stalls.
- Not chocking the tractor. It creeps when the load changes.
- Misaligned pulleys. The belt walks off or wears out.
- Reaching in to clear a jam while the shaft turns. Shut down first.
- Running a PTO generator at the wrong speed. Output and equipment suffer.
Safety
A turning PTO shaft takes in clothing and limbs
PTO entanglements cause severe injuries within a fraction of a second. Keep the shaft guard and belt guards on, never step over or across a turning shaft, tie back hair and avoid loose clothing, and shut the engine off and wait for the shaft to stop before reaching in. Run the tractor outdoors, because its exhaust contains carbon monoxide; see CO Risk. Chock the wheels so the tractor cannot move.
What’s Next
- Learn next: Power Transmission — losses and alignment between a power source and machinery
- Combine with: Alternator as Generator — electricity from a spinning shaft