Build a Pulley

Widely known as one of the “simple machines,” pulleys are among the earliest machines ever used by humans. A pulley is composed mainly of a wheel fixed to an axle, around which a rope is wrapped that can be used to lift and move weighty objects. This allows you to change the direction of your work -- pulling down on a rope, for example, to raise a box upwards. Pulleys can be fixed, movable, or compound.

Steps

Building Simple Fixed Pulleys

1. Round up the necessary supplies. Pulleys are simple machines, and excellent ways to teach kids about forces, gravity, and efficiency. To make simply pulleys, you should round up the following supplies, though there are substitutes available if you're missing something. They will be discussed later.
   • Wire coat hanger
   • String, rope, or cord (at least 10 feet)
   • Wooden spool, like those found for thread (with a hole through the center)
   • A weight to test, like a half-filled milk jug, book, piece of pipe, etc.
2. Cut the wire hanger at the bottom, right in the middle. Open it up so that you can thread the spool through the coat hanger. The spool, which will function as you pulley, in the center of the wire. The top of the hanger can be held or hung from the ceiling to make your pulley free-standing. If you don't have a coat hanger, you can use:
   • Long skewers, dowels, or rods that you hold on either side.
   • String threaded through the spool, then tied up above.
3. Thread the open ends of the wire through the spool. Gently pry the cut in the wire open and put the spool on the coat hanger. The less you try and bend things, the easier it will be to get the spool on while keeping the wire in place.If you can't get a wooden spool, try out:
   • Pre-made pulley wheels, found at most hardware stores for $5 or less.
   • Pulley wheels found in toy sets, like K'Nex building blocks.
   • Old ribbon spool, like for ribbon used in gift wrapping.
   • Toilet paper or paper towel roll, in a pinch.
4. Close off the wire hanger so that the spool stays in place. You may have to bend the wire right around the spool, kinking it slightly to keep the spool in place if it is too heavy for the wires. A good way to do this is to push both sides of the hanger close together so it is about half as wide as it was originally, then turn the two ends up so nothing can slide past them.
5. Loop the string over the top of the pulley. It isn't a complicated stringing. You just want the string draped over the top of the pulley. When you pull down on one end of the string, the other end will get shorter as it moves up.
   • If you plan on doing a lot of experiments with pulleys, you could tie a small metal hook to one end of the string, allowing you to hang and test different weights from it with ease.
6. Hang the pulley system up, making sure it can spin freely. Hang the top of the clothes hanger up so that the spool and string hang and can spin with ease. You could have a friend hold the top of the clothes hanger as well. If you're using a rod or towel around the spool, you can place two chairs near each other and balance the dowel on the tops of the two backs.
7. Tie the weight to one end of the string, Pulley's make your work easier by distributing the weight and forces across the "different" sides of strings created by the pulley. It also makes it easier to pick something up, because you get to pull the string down, using gravity to assist you. Feel how heavy your weight (half-full milk container, textbook, etc.) is before trying it on the pulley for comparison.
   • If you and your school have force meters, use them to test and record the weight before using a pulley.
8. Pull down on one end of the rope to bring the weight up with ease. Even rough pulleys (the wheel doesn't turn well, the string catches, etc.) will make it easier to pull up the book. Why? Because you're moving with gravity by pulling down, making the motion more efficient. More complicated and fine tuned pulleys, called "block and tackle" can even make it possible for one person to lift a car by themselves, though they require many pulleys acting together. Test the weight with a force meter to see just how much easier your pulley makes lifting things.
9. Ask yourself some questions, adjusting the pulley to test your experiment. Do things happen if the string gets longer? What if you used a bigger or smaller pulley wheel? Pulleys teach a lot about forces, gravity, and machines -- what can you learn? Focus on finding ways to make the pulley more efficient to test how each part works.
   • What would happen if you added two more pulleys to the system, threading the string through them? Would it get easier to lift or harder? Easier.
   • Does the weight raise up the same amount as you pull the string back? Yes -- the length of the string stays the same, so the length on both sides of the pulley will always add up to the same number

Building a Fixed Pulley

1. Choose a weight-bearing installation spot in your ceiling. You'll need to screw the pulley into a ceiling joist or rafter, not just the drywall on the ceiling. Pulley's are made to handle heavy objects with ease, but this weight will all have to be carried by the screws in the ceiling. If you don't know how to find the right spot for installation, you may want to hire outside assistance building a pulley.
2. Purchase a simple fixed pulley system. You can, of course, try and craft your own pulley wheel, buy an axle, and then get a mounting bracket that fits your wheel and axle. However, when most simply pulley wheels and brackets are already less than $20, this isn't really worth the risk. A pre-purchased system has everything already measured and tested, ensuring it fits.
3. Run the axle through the center of the wheel. If your wheel doesn’t include an axle that you can easily secure to an installation spot, you’ll need to insert an axle yourself. Simply run it through, placing a little WD40 along the length if it is sticking at all.
4. Secure the axle to the ceiling using the screws included. Attach the axle securely to a wall or ceiling using appropriate hardware. You’ll usually want to use hammer and nails to hammer the axle in place, or use a power drill and long screws for higher-weight systems. Again, if this makes you uncomfortable, you should likely call a professional handyman or experienced friend.
   • Oftentimes your "block," or the fixed pulley, will have a hook. In this case, simply bolt a ring to the ceiling and hook the block onto the ring.
5. Ensure that the wheel can spin freely. Make sure that you wheel can move without resistance. Tighten all the screws so that nothing is jiggling, and use a little mechanical grease in the moving parts if there are any sticky spots.
6. Thread the rope on the top of the pulley. You thread the rope along the “track” or sheave running between the grooves around the outside of the wheel. Make sure it is on the top half.
7. Tie the weight to one end of the string or attach a hook to make a reusable pulley. Take the end of the string you won't be pulling and attach a weight. You could tie the string to the object or create a simple hook.
8. Test the pulley. Pull on the other end of the rope and let the pulley change the direction of the force. If the pulley works, you should be able to raise the object all the way up to the axle.

Building a Compound (Moving) Pulley

1. Diagram the pulley system before buying or installing anything. Pulley systems are a great way to lift heavy objects with minimal effort, but they need to be properly set up to have any chance of working. Look up specific diagrams online, as people have posted systems for every variety of pulley imaginable. Know, as you read the schematics, the differences in pulleys:
   • Fixed: The pulley wheel spins, but the whole thing stays in place. The rope is simply draped over the top. You pulling down on one half of the rope pulls the other half up. There is an axle in the middle of the wheel.
   • Movable Pulley: The pulley has a hook in the center, not an axle. As such, it is almost always used with other pulleys. As you pull the rope, the area around the pulley shortens, lifting/lowering the weight and pulley together. The weight is usually attached to pulley by the hook.
   • Double pulley: Best seen in an example: think of a hanging PowerPoint screen. You pull the cord on one side, but both sides go up identically -- this is because the same rope is looped on both sides. It goes through the left side, to the right, then back to the double pulley on the left, where you pull the string down.
   • Build a Block and Tackle. The block and tackle just refers to the apparatus of pulleys and rope you’re using, where the rope is threaded 2-4 times on the same pulley. Block and tackles usually come with specific instructions for assembly.
2. Ensure you have a secure platform to adhere the pulleys too. You want everything to be on a load-bearing post or stud. If you don't have secure areas close together for the screws, you can build a platform. Attach two blocks to a 2x4 plank. These are known as the “standing blocks” because they stand in a fixed position to form fixed pulleys. Then attach the plank securely to your ceiling or roof. Attach them about a foot apart on a standard 2x4.
   • The 2x4 should be high enough to be slightly above the position where you want to lift the object with the compound pulley.
3. Install your pulleys to the plank or ceiling according to your schematic. For this example, you can use the most common M-shaped compound system. To do so, you install your pulleys in a line, with the two fixed pulleys on the outside and the moving pulley in the middle. The movable pulley is not installed into the ceiling, however -- it will be held up by the rope. For now, line up the two fixed pulleys and install them.
   • Make sure you use a level, straightedge, and careful measurement to ensure that the two fixed pulleys are aligned.
   • There should be the same amount of space between each fixed pulley and the movable pulley in the center.
4. Feed rope through the bottom of the movable pulley. Begin using the rope on the third pulley, the one that is not attached to the board. This is called the moving block. The rope goes on the bottom of the wheel, and most movable pulleys have a small metal tab to keep the rope from coming out.
5. Insert the rope into the other two pulleys. Feed each side of the rope through the other two pulleys. The movable pulley will now be hanging from the tops of the two fixed pulleys. The rope will be on top of each fixed pulley and at the bottom of the movable one.
   • The rope should look a bit like an "M." It will drape down from either pulley on the end. and come down to a "point" around the movable pulley in the middle.
6. Secure the object you want to lift to the movable pulley. Attach whatever you’re lifting to the bottom of the movable pulley, securing it to the hook. You may need to step on or hold the rope to keep it from yanking down if you don't have a lot of slack.
   • Consider attaching a bucket or toolbox to the movable pulley. That way, you can easily transport multiple objects or objects that don’t attach well to the pulley itself.

Warnings

• Use caution when using your pulley to lift extremely heavy objects, as there is a risk of damage to the wall or ceiling.

Things You'll Need

Fixed Pulley

• Grooved wheel and axle (or a wheel-and-axle combination)
• Rope
• Screws, screw ring, or other hardware for securing pulley
• Screwdriver or powered drill to assist in attaching pulley

Compound Pulley

• 3 blocks
• 2x4 in. plank
• Rope
• Screws, screw ring, or other hardware for securing pulley
• Screwdriver or powered drill to assist in attaching pulley

Related Articles

• Use Pulleys

Sources and Citations

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