Simple Machines
Why This Matters
A person can lift about 25 kg overhead. With a simple lever, that same person lifts 250 kg. With a block and tackle, they hoist a 400 kg roof beam into place alone. Simple machines are not primitive — they are the foundation of every crane, every engine, and every factory ever built. Understanding the six simple machines and how to combine them is the single biggest force multiplier available to a rebuilding community. These principles do not wear out, do not need fuel, and scale from moving a single boulder to constructing multi-story buildings.
What You Need
General materials for building simple machines:
- Hardwood logs and planks (oak, ash, hickory, or similar dense wood)
- Metal rods, pipes, and flat stock (salvaged or forged)
- Rope — strong cordage, minimum 10 mm diameter for lifting loads over 50 kg (see Knots & Cordage)
- Grease or oil (animal fat, plant oil, or petroleum grease) for bearings
- Basic tools: saw, hammer, chisel, drill, file, knife
For pulleys and hoists:
- Wooden or metal wheels/discs, 10-30 cm diameter
- Axle pins (metal rods or hardwood dowels)
- Hooks or carabiners (forged or salvaged)
For gears:
- Hardwood blanks at least 5 cm thick (maple, oak, or similar)
- A compass or dividers for marking teeth
- A chisel set and coping saw for cutting teeth
For bearings:
- Hardwood blocks (lignum vitae is ideal, but any dense hardwood works)
- Metal tubing or pipe for sleeves
- Grease — lots of it
The Six Simple Machines
Every complex machine ever built — from a Roman crane to a modern engine — is a combination of these six fundamental devices. Each one trades force for distance or distance for force. This tradeoff is called mechanical advantage.
1. The Lever
A rigid bar that pivots on a fixed point called a fulcrum. When you push down on one end, the other end pushes up. The farther your end is from the fulcrum relative to the load end, the more force you gain.
The three classes:
Class 1 — Fulcrum between effort and load. Examples: seesaw, crowbar, scissors. This is the most common and most versatile arrangement. If the effort arm is 3 times longer than the load arm, you get 3:1 mechanical advantage — you push with 10 kg of force and lift 30 kg.
Class 2 — Load between fulcrum and effort. Examples: wheelbarrow, nutcracker, bottle opener. The load is always closer to the fulcrum than your effort, so you always get a mechanical advantage greater than 1.
Class 3 — Effort between fulcrum and load. Examples: tweezers, fishing rod, human forearm. You sacrifice force for speed and range of motion. Mechanical advantage is less than 1, but the load moves faster and farther than your hand.
Mechanical Advantage Formula:
MA = Length of effort arm / Length of load arm
Example: A 3-meter bar with the fulcrum 0.5 meters from the load end:
- Effort arm = 2.5 m
- Load arm = 0.5 m
- MA = 2.5 / 0.5 = 5:1
- You push with 20 kg of force and move 100 kg
Practical tip: For prying boulders out of the ground, use the longest, strongest bar you can find. A 4-meter steel pipe or hardwood pole with the fulcrum (a rock) placed close to the boulder gives you enormous leverage.
2. The Wheel and Axle
A large wheel attached to a smaller axle. When you turn the wheel, the axle turns with much more force (but less distance). When you turn the axle, the wheel turns with much more speed (but less force).
Mechanical Advantage Formula:
MA = Radius of wheel / Radius of axle
Example: A 60 cm wheel on a 5 cm axle: MA = 30/2.5 = 12:1. This is why a hand-cranked winch with a large handle and small drum can lift enormous weights.
Practical applications:
- Winch: Large crank handle on a small drum wraps rope and lifts heavy loads
- Wagon wheels: Allow heavy loads to roll instead of drag, reducing friction dramatically
- Potter’s wheel: Large flywheel stores momentum, keeps the wheel spinning steadily
- Grinding wheel: Foot pedal (large circle) drives a small grinding stone at high speed
Building a basic winch:
- Mount a strong axle (5-8 cm diameter steel pipe or hardwood) between two upright posts
- Attach a handle arm extending 40-60 cm from the axle center (this is your “wheel”)
- Wrap rope around the axle
- Add a ratchet — a pivoting pawl that catches on notches cut into a disc on the axle — to prevent the load from unwinding when you release the handle
- This simple winch gives you 8-12:1 mechanical advantage
3. The Pulley
A wheel on an axle with a groove for a rope. A single fixed pulley changes the direction of force — you pull down, the load goes up — but does not multiply force. The magic happens when you combine multiple pulleys.
Single fixed pulley: MA = 1 (no force gain, but you can pull downward to lift upward, using your body weight)
Single movable pulley: MA = 2 (the load hangs from a pulley that moves, and both sides of the rope support the load)
Block and tackle: Multiple pulleys combined. Each additional rope segment supporting the load adds 1 to the mechanical advantage.
The rule: Count the number of rope segments pulling up on the movable block. That number is your mechanical advantage.
MA = Number of rope segments supporting the load
| Configuration | Rope Segments | MA | 100 kg Load Requires |
|---|---|---|---|
| Single fixed | 1 | 1:1 | 100 kg pull |
| Single movable | 2 | 2:1 | 50 kg pull |
| Double (2 fixed + 2 movable) | 4 | 4:1 | 25 kg pull |
| Triple (3 fixed + 3 movable) | 6 | 6:1 | 17 kg pull |
The tradeoff: For every unit of mechanical advantage, you must pull that many extra meters of rope. A 6:1 block and tackle lifting a load 1 meter requires pulling 6 meters of rope.
4. The Inclined Plane
A flat surface tilted at an angle — a ramp. Instead of lifting a 200 kg barrel straight up onto a 1-meter-high wagon, you roll it up a 4-meter-long ramp and use only a quarter of the force.
Mechanical Advantage Formula:
MA = Length of ramp / Height of rise
Example: A 6-meter ramp to reach a 1.5-meter height: MA = 6/1.5 = 4:1. You push with 50 kg of force to move a 200 kg barrel.
Practical applications:
- Loading wagons and boats
- Moving stones up to construction height (this is how pyramids were built)
- Roads through hilly terrain — switchback roads are just long inclined planes
- Drainage ditches (water flows down the “ramp”)
5. The Wedge
An inclined plane that moves. Instead of moving the object along the ramp, you drive the ramp into the object. Axes, knives, chisels, and splitting wedges all work on this principle.
Mechanical Advantage Formula:
MA = Length of wedge / Width of thick end
A splitting wedge that is 20 cm long and 4 cm wide at the thick end has a 5:1 mechanical advantage. Your hammer blow is multiplied five times as the wedge converts downward force into sideways splitting force.
Practical tip: For splitting logs, use a narrow, long wedge for hardwood (higher MA, slower splitting) and a wider, shorter wedge for softwood (faster splitting, less MA needed). Always use metal wedges for serious work — wooden wedges compress and lose energy.
6. The Screw
An inclined plane wrapped around a cylinder. Each turn of the screw advances it by one pitch (the distance between threads). A screw with a 1 mm pitch turned by a handle with a 100 mm radius has a mechanical advantage of about 628:1. This is why screws hold so tightly and why screw jacks can lift buildings.
Mechanical Advantage Formula:
MA = (2 x pi x handle_radius) / pitch
Example: Handle radius 150 mm, pitch 3 mm: MA = (2 x 3.14 x 150) / 3 = 314:1
Practical applications:
- Screw jack: Lifts buildings, presses olives, compresses bales
- Vise: Clamps work securely for metalworking or woodworking
- Screw press: Presses paper, cheese, cider, or linen
- Auger: Drills holes in wood or earth
Method 1: Building a Block and Tackle
A block and tackle lets a single person lift loads that would normally require a team. This is the most immediately useful simple machine project you can build.
Building the Blocks
Step 1 — You need two blocks: an upper (fixed) block and a lower (movable) block. For a 4:1 system, each block holds two pulleys. For a 6:1 system, the upper block holds three pulleys and the lower holds three.
Step 2 — Carve or cut pulley wheels from hardwood. Each wheel should be 10-15 cm in diameter and 2-3 cm thick. Cut a V-shaped or U-shaped groove around the circumference for the rope to sit in. The groove depth should be about half the rope diameter.
Step 3 — Drill a center hole in each wheel, slightly larger than your axle pin (1-2 mm clearance). The axle can be a metal rod, bolt, or hardened wooden dowel. The wheel must spin freely on the axle.
Step 4 — Build the block frames from two parallel hardwood plates (cheeks), about 20 cm tall, 8 cm wide, and 2 cm thick. Space them apart just enough to fit the pulley wheels between them, with 2-3 mm clearance on each side.
Step 5 — Drill axle holes through both cheek plates at the same height. Insert the axle through one cheek, through the pulley wheel(s), and through the other cheek. Secure the axle with cotter pins, bent nails, or wooden wedges.
Step 6 — For the upper block, attach a strong hook or loop at the top for hanging from a beam or tripod. For the lower block, attach a hook or loop at the bottom for attaching to the load.
Reeving the Rope
Step 7 — Use rope that is strong enough for your loads. A general rule: the rope must handle (Total Load / Mechanical Advantage) plus about 30% for friction. For a 400 kg load on a 4:1 system, each rope strand carries about 130 kg (100 kg plus friction) — use rope rated for at least 150 kg.
Step 8 — Tie one end of the rope to the upper block frame. Thread the rope down around the first pulley in the lower block, up around the first pulley in the upper block, down around the second pulley in the lower block, and up around the second pulley in the upper block. The free end (where you pull) comes out of the upper block.
Step 9 — For a 4:1 system, you should see 4 rope segments running between the upper and lower blocks. Pull on the free end — the lower block should rise smoothly.
Using the Block and Tackle
Step 10 — Hang the upper block from a strong overhead point: a tripod of heavy poles lashed together, a thick tree branch, or a beam built into a structure. The anchor point must support the full weight of the load.
Step 11 — Hook the load to the lower block. Pull the free end of the rope. With a 4:1 advantage, pulling with 25 kg of force lifts 100 kg (minus friction losses, typically 10-15% per pulley).
Step 12 — To hold the load in position, tie off the free end to a cleat (a wooden or metal post with horns for wrapping rope) or use a cam cleat. Never hold a heavy suspended load by hand alone.
Tip
Grease the axle pins regularly. Dry wooden pulleys lose 15-20% of your mechanical advantage to friction. Well-greased pulleys lose only 5-10%.
Method 2: Building Wooden Gears
Gears transfer rotation from one shaft to another and can change speed, direction, and torque. Wooden gears were used in mills, clocks, and machinery for thousands of years before metal gears became common.
Designing the Gears
Step 1 — Decide on your gear ratio. If you want the output shaft to spin 3 times faster than the input shaft, the input (driving) gear must have 3 times as many teeth as the output (driven) gear. Example: 36-tooth driver, 12-tooth driven = 3:1 speed increase.
Step 2 — Choose a tooth pitch (the distance from one tooth center to the next, measured along the pitch circle). For wooden gears, a pitch of 15-25 mm works well. Smaller pitch means more teeth and smoother operation, but the teeth are harder to carve accurately.
Step 3 — Calculate the number of teeth and the pitch circle diameter:
Pitch Circle Diameter = Number of Teeth x Pitch / pi
For a 24-tooth gear with 20 mm pitch: Diameter = 24 x 20 / 3.14 = 153 mm
Step 4 — Cut a disc of hardwood (maple, oak, or similar) to the calculated diameter, at least 4-5 cm thick. The face grain should be perpendicular to the axis — do not use end grain, as teeth will break off.
Cutting the Teeth
Step 5 — Mark the pitch circle on the disc face (a circle at the radius where the teeth of the two gears will mesh). Use a compass or dividers.
Step 6 — Divide the pitch circle into equal segments for each tooth. Use dividers set to the pitch distance and walk them around the circle. Mark each tooth center.
Step 7 — Each tooth profile should be roughly trapezoidal: wider at the base, narrower at the tip. The tooth height (from root to tip) should be about 2 times the pitch divided by pi (roughly 0.6 x pitch). For 20 mm pitch, teeth are about 12 mm tall above the root.
Step 8 — The tooth width at the pitch circle should be about half the pitch (10 mm for a 20 mm pitch). The gap between teeth (the space where the mating gear’s teeth fit) is also half the pitch.
Step 9 — Cut the tooth profiles with a coping saw, then refine with a chisel and file. Cut slightly oversize and file down to the lines. The accuracy of the tooth spacing matters more than the exact tooth shape — uneven spacing causes binding and vibration.
Step 10 — Drill a center hole for the axle. The hole must be perfectly centered or the gear will wobble. If you have a lathe (even a simple pole lathe), turn the gear on the lathe for best concentricity.
Assembling the Gear Train
Step 11 — Mount both gears on their respective shafts. The shafts should be parallel, with the gear faces aligned. The shaft spacing must equal the sum of both pitch circle radii — too close and the gears bind, too far and they skip.
Step 12 — For the shafts, use bearing blocks mounted on a rigid frame. Both shafts must stay precisely parallel as they turn. A frame of heavy timber, bolted or pegged together, works well.
Step 13 — Test the mesh by turning the gears slowly by hand. They should roll smoothly with minimal backlash (play between teeth). If teeth bind, file the tight spots. If there is too much backlash, the shafts are too far apart.
Step 14 — Apply grease or tallow to the tooth faces. Wooden gears need lubrication to reduce wear. In medieval mills, wooden gears lasted years with regular greasing. Without grease, they wear out in weeks of heavy use.
Tip
A common trick from historical millwrights: make the smaller gear from a harder wood than the larger gear. The small gear turns faster and wears more — using harder wood (or even metal teeth pegged into a wooden hub) for the small gear extends the life of the system.
Lantern Gears (Simpler Alternative)
If carving involute-profile teeth seems too difficult, build a lantern gear instead. This is a cylinder of two parallel discs connected by evenly spaced round dowel pins around the circumference. The pins act as teeth and mesh with a standard flat-toothed gear (called a “face gear” or “crown gear”).
Step 1 — Cut two wooden discs the same diameter. Drill matching holes around the edge, evenly spaced.
Step 2 — Insert hardwood dowels (1-2 cm diameter) into the holes, connecting the two discs like a hamster wheel or lantern.
Step 3 — The mating gear has flat, rectangular teeth spaced to fit between the dowels. This is much easier to carve accurately than matched curved tooth profiles.
Lantern gears were used in windmills and water mills across Europe and Asia for centuries. They are rough but effective.
Method 3: Building a Wheelbarrow
The wheelbarrow combines a wheel and axle (Class 2 lever) into one of the most useful tools for a rebuilding community. It turns heavy, awkward loads into manageable ones.
Building the Frame
Step 1 — Cut two straight handles from strong hardwood, each about 150 cm long and 4-5 cm in diameter. These serve as both handles and the main structural members. Shave or plane them smooth where your hands grip.
Step 2 — At the front end (where the wheel will go), angle the two handles inward until they nearly meet, leaving a gap of about 5 cm. These front ends will hold the axle.
Step 3 — Drill a hole through each front end for the axle. The holes must be perfectly aligned so the wheel spins freely.
Building the Wheel
Step 4 — A simple solid wheel works fine for a wheelbarrow. Cut a disc from a thick hardwood plank (or laminate several thinner planks together with pegs and glue), about 35-45 cm in diameter and 5-8 cm thick.
Step 5 — Drill a center hole for the axle. The axle should be a metal rod or pipe, 1-2 cm diameter. The wheel must spin freely on the axle with minimal wobble.
Step 6 — For a longer-lasting wheel, add a metal tire — a strip of flat iron bent into a circle and nailed or bolted around the wheel’s circumference. Heat the iron band so it is slightly smaller than the wheel, fit it on, then quench with water. As it cools, it shrinks and grips the wheel tightly (this technique is called “shrink fitting”).
Building the Bed
Step 7 — Build the load bed between the two handles, starting about 40 cm behind the axle and extending about 60-80 cm back. Nail or peg cross-pieces between the handles, then nail planks across the cross-pieces to form a flat or trough-shaped bed.
Step 8 — For carrying loose material (dirt, gravel, sand), add side boards 15-20 cm high. Angle the front board to form a sloped nose that helps dump loads forward.
Step 9 — Add legs — two short wooden posts (10-15 cm long) under the bed near the handles. These let you set the wheelbarrow down without it tipping.
Assembly and Use
Step 10 — Insert the axle through both handle ends and the wheel. Secure the axle with cotter pins, washers, or bent nails on the outside of each handle so the wheel stays centered.
Step 11 — The mechanical advantage of a wheelbarrow depends on where the load sits. The closer the load is to the wheel, the less effort you need to lift the handles. A load centered directly over the axle requires almost zero lifting force — you just push forward. A load at the back near the handles gives almost no mechanical advantage. Always load heavy items toward the front.
Mechanical advantage: If the load center is 30 cm from the axle and your hands are 120 cm from the axle, your MA = 120/30 = 4:1. You lift 25 kg to carry 100 kg.
Tip
On soft or muddy ground, a wider wheel sinks less. Consider building a wheel 10-15 cm wide instead of the standard 5-8 cm. For very soft ground, two wheels side by side (making a two-wheeled cart) are more stable, though you lose some of the single-wheel wheelbarrow’s maneuverability.
Bearings: The Hidden Key to All Machinery
Every spinning axle needs a bearing — the interface between the moving shaft and the stationary frame. Bad bearings waste energy, wear out shafts, and cause machines to seize. Good bearings make everything work better.
Types of Bearings You Can Build
Plain journal bearings: A hole in a block of material, slightly larger than the shaft. The shaft spins inside the hole with grease in the gap. This is the simplest and most common type for hand-built machinery.
- Best wood: Lignum vitae (self-lubricating, incredibly dense). If unavailable, use the hardest, densest wood you can find — ironwood, boxwood, hard maple.
- Hole clearance: The hole diameter should be 1-2 mm larger than the shaft. Too tight and it binds. Too loose and it wobbles and wears unevenly.
- Lubrication: Pack grease (animal fat mixed with fine ash or graphite works well) into the bearing. Re-grease whenever the bearing gets warm to the touch or starts squeaking.
Metal sleeve bearings: A short section of metal pipe or tubing, pressed into a wooden block, with the shaft spinning inside it. More durable than wood alone. Bronze or brass pipe is ideal (low friction, resists corrosion).
Ball bearings (salvaged): If you can find ball bearings from old machinery, vehicles, or appliances, use them. They are far superior to anything you can build. Protect them from dirt and water, keep them greased, and they will last for years.
Thrust bearings: For vertical shafts or axial loads, you need a bearing that handles force along the shaft’s length. A simple thrust bearing: a hardwood disc spinning on a greased metal or stone plate. Water mills use this for the vertical main shaft.
Bearing Maintenance
- Check bearings weekly on any machine that runs regularly
- Feel for heat — a warm bearing needs more grease or has too much friction
- Listen for squealing — this means metal-on-metal contact and imminent failure
- Replace worn bearings before they damage the shaft
- Keep dirt and grit away from bearings — a single grain of sand accelerates wear dramatically
Common Mistakes
| Mistake | Why It’s Dangerous | What to Do Instead |
|---|---|---|
| Ignoring friction in mechanical advantage calculations | Real-world friction losses are 10-30%, so your actual lifting capacity is lower than the formula suggests | Add 30% to your calculated effort, and grease all bearings and pulleys |
| Using green (unseasoned) wood for gears and pulleys | Green wood shrinks as it dries, changing dimensions — teeth no longer mesh, axle holes become oval | Use seasoned wood (air-dried at least 6 months) for all precision parts |
| Overloading a block and tackle beyond rope capacity | The rope fails suddenly, dropping the load — this kills people | Rate your system by the weakest component (usually the rope), and never exceed 50% of rated capacity |
| Building gears with uneven tooth spacing | Uneven spacing causes binding, vibration, and rapid wear | Measure tooth positions precisely with dividers; test mesh by hand before loading |
| No ratchet or brake on winches and hoists | The load runs backward when you release the handle, with extreme speed and force | Always build a ratchet, cam cleat, or braking mechanism into any lifting device |
| Dry bearings | Unlubricated bearings generate friction heat, char wood, score metal, and seize | Grease every bearing before use and on a regular schedule |
| Anchoring a pulley system to a weak point | The anchor carries the full load plus your pulling force — if it fails, everything falls | Anchor to structures rated for at least 3x the load weight |
| Making axle holes too tight | The shaft binds, wastes energy, and wears rapidly | Leave 1-2 mm clearance and lubricate |
What’s Next
With simple machines understood and built, you can move on to:
- Water Systems — use pumps, levers, and pulleys to move water uphill and distribute it to your settlement
- Structural Engineering — apply force analysis to design buildings, walls, and foundations that last
- Steam Engine — combine pistons, cranks, flywheels, and valves into a heat-powered engine
- Hydro Generator — use water wheels and gearing to generate electricity
Quick Reference Card
Simple Machines — At a Glance
The six simple machines and their MA formulas:
Machine MA Formula Example Lever Effort arm / Load arm 3m bar, fulcrum 0.5m from load: MA = 5 Wheel & Axle Wheel radius / Axle radius 30cm wheel, 2.5cm axle: MA = 12 Pulley (block & tackle) Number of supporting rope segments 4 ropes: MA = 4 Inclined Plane Ramp length / Rise height 6m ramp, 1.5m high: MA = 4 Wedge Length / Width at thick end 20cm long, 4cm wide: MA = 5 Screw 2 x pi x handle radius / pitch 150mm handle, 3mm pitch: MA = 314 Key rules:
- MA trades force for distance: 4:1 MA means you pull 4x the distance with 1/4 the force
- Always add 30% to calculated effort for real-world friction
- Grease all bearings and pulleys — friction is the enemy
- Never exceed 50% of rope’s rated breaking strength for lifting
- Anchor points must support 3x the load weight minimum
Quick pulley guide:
- 2:1 — one movable pulley (one person lifts 50 kg)
- 4:1 — two pulleys per block (one person lifts 100 kg)
- 6:1 — three pulleys per block (one person lifts 150 kg)
When in doubt: A block and tackle is the most universally useful machine you can build. Start there.