Do-it-yourself mechanisms for lifting loads. Garage: homemade lifting devices

Lifting heavy loads to a height, even if not very large, is a very difficult task for a person. However, many different mechanisms and devices have been invented to facilitate this process. These mechanisms must include a pulley block. In our article, we will talk in more detail about this device, and also talk about the technology for creating a chain hoist at home.

How can you make lifting loads easier

The polyspast is a system that consists of fixed and movable blocks connected to each other by chain or cable drives. This device was invented a long time ago, because even the ancient Greeks and Romans used similar mechanisms. Over the next millennia, the components of this device and its purpose have practically not changed. Today this device is used practically in its original form, with only minor changes.

The scheme of the pulley block

Polypastas are mainly used in jib mechanisms of construction cranes. Despite all their diversity, there are two main requirements for pulley blocks: an increase in speed (high-speed mechanisms are responsible for this) and an increase in strength (the so-called power pulley blocks). In hoists, the former are usually used, while the latter are used in cranes. It should also be noted that the important fact that the circuits of power and high-speed devices are almost completely mutually inverse.

A conventional pulley block is a device whose main components are:

block system with movable axles;
blocks with fixed axles;
bypass drums;
bypass blocks.

Due to the effective interaction of blocks and ropes, it becomes possible to significantly win in strength. In strength, we win as many times as we lose in length. This is one of the fundamental rules of mechanics, thanks to which an ordinary person can easily lift heavy masses with a minimum of physical effort.

It is much more profitable to purchase this device or make it yourself, rather than renting cranes or similar mechanisms. The peculiarity of the device lies in the fact that one of the sides, which is fixed to the load, is in a movable state, while the other side, which is attached to the support, is static. It is the moving blocks that provide such a significant gain in strength. Static blocks are required to control the trajectory of the rope and the load itself.

There are different types of chain hoists, which differ in multiplicity, parity and complexity. The multiplicity indicator determines how many times you will gain in strength using a given device. So, buying a mechanism with a multiplicity of 6, you theoretically have a gain in strength 6 times.

Simple and complex pulley blocks - we understand their design

First, let's talk about simple mechanisms. You can get such a device by adding blocks to the load and support. An even pulley block is a device in which a rope is attached to a support. If an odd one is required, then the rope is installed on a movable point of the object being lifted. Adding a block increases the multiplicity of the device by two points.

So, to manually make a chain hoist for an ordinary winch, the multiplicity of which is 2, it is enough to use only one movable block attached to the load. The rope is attached to the support. As a result, we will have an even chain hoist with a multiplicity of 2. Complex chain hoists include several simple mechanisms. Naturally, such a device gives a significantly greater gain in power, which can be calculated by multiplying the multiplicities of each of the used chain hoists. In this case, do not forget about the friction force, due to the action of which there is a small loss in the power of the device.

There are several ways to reduce the friction of the rope. The most effective is to use rollers with the largest radius possible. After all, the larger the radius, the less frictional force exerts on the rope and the lifting mechanism as a whole.

How rope affects performance

You can avoid pinching and twisting the rope by using additional devices, for example, mounting plates, which allow the rollers to be spaced relative to each other. We strongly do not recommend using stretching ropes in chain hoists, since in comparison with ordinary static products they are very seriously inferior in efficiency. When assembling a block for lifting loads, specialists use both a load and a separate rope, which are attached to the object independently of the lifting device.

There are some advantages to using individual ropes. The bottom line is that a separate rope provides the opportunity to pre-or pre-assemble the entire structure. In addition, the passage of knots can be greatly facilitated since the entire length of the rope is used. The only drawback is the inability to fix the load in automatic mode. Cargo ropes can boast of just such a feature, so if you need to auto-fix the load, use the cargo rope.

The reverse is of great importance. This effect is inevitable, since at the moment of removal, as well as when intercepting the rope or stopping for rest, the load will certainly move in the opposite direction. The quality of the blocks used, as well as the entire device as a whole, determines how much the load will go back. This phenomenon can be prevented by purchasing special rollers that allow the rope to pass only in one direction.

Let's talk a little about how to properly attach a load rope to the lifting mechanism. Even the most prudent craftsman does not always have a rope of the required length, which is required to fasten the dynamic part of the block. Therefore, several methods of fastening the mechanism have been developed:

With grasping knots. These knots are tied in five turns from cords, the cross-section of which does not exceed 8 mm. The use of such nodes is the most effective and, accordingly, widespread. According to experts, the knots are very strong and reliable. Only a load in excess of 13 kN can lead to sliding of such a unit. The important thing is that even when sliding, the knot does not deform the rope in any way, leaving it intact.
The use of clamps for general purposes. These devices can be used even in difficult climatic conditions, for example, on wet or ice-covered ropes. A load of 7 kN can cause the clip to slip, causing damage to the rope, albeit not very severely.
Personal clamps. They are used only for small jobs, since a load over 4 kN will cause the clamp to slip and the rope to break.

Stocking - we study the most popular schemes

This technological operation is intended to change the distance between the blocks, as well as to change the position of these blocks. The need for stocking is due to a change in the height or speed of lifting objects by setting a specific pattern for the rope to pass through the blocks and rollers of the mechanism.

The scheme used largely depends on the type of lifting device. The hoists are only stocked to change the boom reach. It is carried out by changing the relative position of the guide blocks. Very often, such an operation is carried out in cargo cranes, where it is required to prevent such an effect as curvilinear movement of weights.

Stocks, depending on the schemes used, are divided into the following categories:

Single entry. This type has found application in small-size lifting cranes, where the hook must be brought on one rope rope. After that, it is required to sequentially conduct static blocks. In the final stage, the hook is wound around the drum. As practice shows, this type of storage is the most ineffective.
Double entry. This type is used in cranes equipped with jib and luffing jib. In this case, fixed blocks are required to be mounted on the boom head, while the other end of the rope is attached to the cargo winch.
Quadruple. It is in demand among pulley blocks, which are used to lift objects of a huge mass. Usually, one of the reeving schemes that have been described earlier is used, with the only difference that they are used separately for each hook block.

We make a chain hoist from paper cups and gears

The devices used in construction are very complex, which is logical, because here it is required to lift large loads to a sufficiently large height. It can be very problematic to understand their design features. What can not be said about home pulley blocks that are used in everyday life. They are so simple and straightforward that anyone can build a chain hoist with their own hands. To do this, we need the following devices:

1. several glasses of paper;
2.scissors;
3. a string or strong thread that acts as a rope;
4. plasticine;
5. plastic hangers.

First of all, you need to make a basket in which the cargo will move. For these purposes, we will use paper cups through which we thread the rope. The chain hoist itself is assembled from hangers. We fix the rope or thread on the top of the hanger, after which we wind it around the crossbar several times. The basket obtained from the glasses should be hung on the lower hanger by the hook. In principle, at this point, the collection of the chain hoist can be considered complete. To lift loads, you just need to use the mechanism correctly. To do this, you need to pull on the free end of the thread, which will lead to the connection of the hangers. Now you can try to lift heavy objects to a height.

There is another way to make a chain hoist with your own hands, which is somewhat more complicated, but it is more efficient and reliable in design. Here we need bearings, a gear, a hook, cables with blocks, as well as a threaded rod. First, we fix the bearings on the hairpin, after which we install the gear on the end of the hairpin, so that it is more convenient and easier to use a homemade chain hoist. It remains only to throw the cable over the gears and fix it, the free end will be equipped with a hook, which is necessary for lifting objects.

Finally, we recall that when working with any chain hoists bought in a store or made at home, you should definitely remember about safety precautions. The structure must be carefully checked for strength and integrity. The loads themselves should be lifted smoothly and carefully, without being located at this time under the suspended object.

On the roof or upper floors, and without special devices it is very difficult. We will describe the process of assembling a simple and reliable construction hoist with your own hands, which alone can lift up to 300 kg.

The device, assembled according to the above diagram, is absolutely mobile and can be brought to a construction site without any problems even by a passenger car with an upper rack.

For assembly you will need:

glued timber 60x40 mm - 10 m;
timber 40x40 - 9 m;
board 25x80 - 16 m;
rigging block with bearing - 2 pcs .;
bearing roller with axle - 4 pcs .;
nylon cable - 12 m;
plywood 15 mm - less than 1 m 2.

Assembling the guides

The lift is a trolley that slides on rollers between two T-rails. To make them, you need good quality wood with a moisture content of no more than 12%: a 60x40 timber and a 25x80 board. Any curvatures are undesirable, the tree should be free of defects.

The bar in the guide plays the role of a distance spacer that sets the distance between the shelves of the brand. It should be 2-3 mm larger than the diameter of the rollers; if necessary, plan the timber along the narrow end and bring it to the required thickness.

To assemble the guide, you need to put a bar between the boards and align them along one edge. In order for the structure to be completely monolithic, it is recommended to coat the contacting edges with PVA glue before assembly.

Fold the parts, align them with a square and secure with clamps. Then fasten the boards and the beam with white anodized self-tapping screws 55 mm long, screw them in a checkerboard pattern with a step in each row of 30-35 cm. You need to fasten both boards with self-tapping screws, so the guides will be less susceptible to warping.

If you want the rails to be longer than the lumber you have available, stack the beams and boards with an overlap of half the length. With proper splicing, the structure will turn out to be extremely strong, it remains only to bring the internal joints of the boards to zero for the smooth movement of the rollers.

After assembling both guides, cover them with two layers of drying oil. Check the width of the roller gap, if necessary finish with an emery cloth. At a distance of 30 mm from the end in the center of the bar in the T-bar, make a through hole with a diameter of 14 mm. Use it to bolt the rails to the crossbars, place wide washers under the nut and bolt head. To avoid shifting the diagonals, make a connection with a half-tree felling.

Cart design

Start by assembling the frame: insert three bars 75 cm long between 130 cm pieces of 40x40 mm timber. Set the middle bar 40-45 cm from the bottom edge. Fasten the joints with self-tapping screws, or better - assemble the frame on the spike joints.

Attach two 80 cm pieces of timber perpendicular to the frame to the bottom beam, insert a 75 cm long bar between their ends and fasten the structure. To strengthen the pallet, make two inclined scarves 60 cm long from a bar or board, cut the edges at an angle of 45 °. Attach the gusset to the pallet 40 cm from the corner.

Cut out a sheet of plywood with dimensions of 83x84 cm and drill 20 mm holes from each edge in 7 cm increments. Through the holes made, screw the bottom of the pallet to the frame with 45 mm self-tapping screws.

If you plan to increase the carrying capacity of your cart, the joints of the pallet frame and gussets must be reinforced with overhead plates and corners, and the plywood at the bottom with metal brackets. Attach padlock loops with a tail length of at least 70 mm to the top corners of the frame. Insert an M14 bolt into the holes and screw the self-locking nut onto it. Under the bolts, you need to pass a piece of cable about 2 meters long and tie it into a loop, to which a traction rope will be attached through a carabiner or thimble.

Brackets for blocks

On the upper and lower crossbars between the guide posts, one rigging block must be fixed. Fastening is possible only by means of a bolted connection with the obligatory installation of wide washers under the nuts, or better - metal plates.

It is recommended to purchase climbing block pulleys with bearing or grooved lifting pulleys. Most of the products have a solid body with tightly fitting cheeks, therefore, it is impossible to drop the cable from the pulley.

If you are trying to adapt your existing casters, provide them with a soothing ear. Roll the steel wire 6 mm thick until a loop is formed, and then bend the edges of the structure at the required distance to fasten it under the nut to the block axis. Equipping the block roller with a swivel will make it easier to lift the load and the cable will last longer.

Rollers and their fastening

For smooth sliding of the trolley, it should be equipped with four roller wheels installed on the sides, 20-25 cm from the corners. Purchase rollers with a maintenance-free bearing and a one-way steel axle at least 20 mm long. Instead of standard rollers, ball bearings with a closed cage and a cage width of at least 25 mm or wheels from old roller skates can be used.

The roller axis must be removed and drilled for its diameter in the center of the plate 40x80 mm. Having inserted the axle into the hole, install it strictly perpendicular to the plate and weld it, then make four holes in the corners for the M8 bolt.

How to improve the lift

A very useful addition, significantly increasing the safety of use, will be the device of landing pockets for fixing the front wheels of the cart in the raised position. This is not only very convenient when unloading, but also makes it possible to use the lift yourself.

For the arrangement of pockets, it is necessary to cut out a part of the back board of the guide, on which the trolley rollers rest. When lifting, the wheel will slip into the formed opening and stop on the U-shaped block, assembled from three bars. To prevent the wheel from accidentally jumping out, leave a small ledge on the board. After unloading, the cart can be easily removed from the landing pockets and lowered down, holding on to the cable.

To lift more load at a time, you can strengthen the vertical frame of the cart and install a movable block on it, but this will increase the length of the rope by 1.5 times. The traction rope, in this case, is attached to one of the corners between the guide and the connecting crossbar, passed into the movable block on the trolley, and then placed in the fixed upper and lower pulleys.

It is also possible to install the gate as on a well for convenient winding of the traction rope. It can be made from a 100x100 mm cut of a bar, brought to a hexagon with a plane. To install the gate, you will need additional L-shaped posts and replacement of the lower crossbar mounting bolts with studs of the appropriate length. The loose bolts must be used to obliquely mate the racks with the rails.

The use of a gate implies an increased danger, because a person is always at the lift. To prevent the trolley from breaking and falling, it is recommended to install the simplest climbing frame near the upper block.

Lifting machines are designed to help a person lift something heavy to a height. At the heart of most lifting mechanisms is a simple block system - a chain hoist. He was familiar to Archimedes, but now many do not know about this ingenious invention. Remembering the physics course, find out how such a mechanism works, its structure and field of application. Having understood the classification, you can proceed to the calculation. To make it work - your attention is the instructions for constructing a simple model.

Block system - theory

The invention of the pulley block gave a huge impetus to the development of civilizations. The block system helped build huge structures, many of which have survived to this day and are puzzling to modern builders. Shipbuilding was also improved, people were able to travel great distances. It's time to figure out what it is - a chain hoist and find out where you can find its use today.

Simplicity and efficiency of the mechanism

The structure of the lifting mechanism

The classic pulley block is a mechanism that consists of two main elements: a pulley; flexible connection

The simplest scheme: 1 - movable block, 2 - stationary, 3 - rope

The pulley is a metal wheel that has a special groove for the cable along the outer edge. A conventional cable or rope can be used as a flexible connection. If the load is heavy enough, use synthetic fiber ropes or steel ropes and even chains. In order for the pulley to rotate easily, without jumps and jamming, roller bearings are used. All elements that move are lubricated.

One pulley is called a block. Polyspast is a system of blocks for lifting loads. The blocks as part of the lifting mechanism can be fixed (rigidly fixed) and movable (when the axis changes position during operation). One part of the chain hoist is attached to a fixed support, the other to the load. Movable rollers are located on the load side.

Fixed block

The role of the fixed block is to change the direction of movement of the rope and the action of the applied force. The role of the mobile is to gain strength.

Movable block

How it works - what's the secret

The principle of operation of a chain hoist is similar to a lever: the effort that must be applied becomes several times less, while the work is performed in the same volume. The cable plays the role of a lever. In the work of the chain hoist, the gain in strength is important, so the resulting loss in distance is not taken into account.

Depending on the construction of the chain hoist, the power gain may be different. The simplest mechanism of two pulleys gives approximately two-fold gain, from three - three-fold, and so on. The increase in distance is calculated according to the same principle. For the operation of a simple chain hoist, a cable is needed twice as long as the lifting height, and if a complex of four blocks is used, then the length of the cable increases in direct proportion to four times.

How the block system works

In which areas is the block system used

Polyspast is a faithful assistant in a warehouse, in production, in the transport sector. It is used wherever you need to use force to move all kinds of goods. The system is widely used in construction.

Despite the fact that most of the heavy work is performed by construction equipment (crane), the chain hoist has found a place in the design of load-handling mechanisms. The block system (pulley block) is a component of such lifting mechanisms as a winch, hoist, construction equipment (cranes of various types, bulldozer, excavator).

In addition to the construction industry, pulley blocks are widely used in the organization of rescue operations. The principle of operation remains the same, but the design is slightly modified. The rescue equipment is made of a strong rope, carabiners are used. For devices of this purpose, it is important that the entire system is quickly assembled and does not require additional mechanisms.

Polyspast as part of a crane hook

Classification of models according to different characteristics

There are many versions of one idea - a system of blocks connected by a rope. They are differentiated depending on the method of application and design features. Get to know the different types of lifts, find out what their purpose is and how the device differs.

Classification depending on the complexity of the mechanism

Depending on the complexity of the mechanism, simple ones are distinguished; complex; complex pulley blocks.

An example of even models

A simple pulley block is a system of rollers connected in series. All movable and fixed blocks, as well as the load itself, are united by one cable. Even and odd simple pulley blocks are differentiated.

Even-numbered are those lifting mechanisms whose end of the cable is attached to a fixed support - the station. In this case, all combinations will be considered even. And if the end of the rope is attached directly to the load or to the place where the force is applied, this structure and all its derivatives will be called odd.

Odd pulley scheme

A complex chain hoist can be called a chain hoist system. In this case, not individual blocks are connected in series, but whole combinations, which may well be used by themselves. Roughly speaking, in this case, one mechanism sets in motion another similar one.

Combining a double and sixfold simple chain hoist gives a complex sixfold option

The complex pulley block does not apply to one or the other type. Its distinctive feature is the rollers moving towards the load. The complex model can include both simple and complex pulley blocks.

Classification by purpose of the lift

Depending on what they want to get when using a chain hoist, they are divided into:

Power;

High-speed.

A - power option, B - high-speed

The power option is used more often. As the name suggests, its job is to provide a power win. Since significant gains require equally significant losses in distance, losses in speed are inevitable. For example, for a 4: 1 system, when lifting a load one meter, you need to pull 4 meters of cable, which slows down the work.

The high-speed pulley block by its principle is a reverse power structure. It does not give a gain in strength, its goal is speed. It is used to speed up work at the expense of the applied effort.

Multiplicity is the main characteristic.

The main indicator that is paid attention to when organizing the lifting of loads is the multiple of the chain hoist. This parameter conventionally indicates how many times the mechanism allows you to win in strength. In fact, the multiplicity shows how many branches of the rope the weight of the load is distributed over.

Kinematic ratio

The multiplicity is subdivided into kinematic (equal to the number of bends in the rope) and power, which is calculated taking into account the overcoming of the friction force by the cable and imperfect efficiency of the rollers. The reference books contain tables that show the dependence of the power ratio on the kinematic ratio at different efficiency of the units.

As can be seen from the table, the power ratio is significantly different from the kinematic. With a low roller efficiency (94%), the actual gain in the power of a 7: 1 chain hoist will be less than the gain of a six-fold chain hoist with a block efficiency of 96%.

Polyspast schemes of different multiplicity

How to make calculations for a chain hoist

Despite the fact that theoretically the design of the chain hoist is extremely simple, in practice it is not always clear how to lift the load using blocks. How to understand what multiplicity is needed, how to find out the efficiency of the lift and each block separately. In order to find answers to these questions, you need to perform calculations.

Calculation of a separate block

The calculation of the chain hoist must be performed due to the fact that the working conditions are far from ideal. Friction forces act on the mechanism as a result of the movement of the cable along the pulley, as a result of the rotation of the roller itself, whatever bearings are used.

In addition, flexible and pliable rope is rarely used on the construction site and in construction equipment. A steel rope or chain is much more rigid. Since additional effort is required to bend such a cable when running onto the block, it must also be taken into account.

For the calculation, the equation of moments for the pulley relative to the axis is derived:

S run R \u003d S run R + q S run R + Nfr (1)

Formula 1 shows the moments of such forces:

- Sbeg - the effort from the side of the runaway rope;

- S run - effort from the side of the oncoming rope;

- q S run - effort for bending / unbending the rope, taking into account its rigidity q;

- Nf - the friction force in the block, taking into account the friction coefficient f.

To determine the moment, all forces are multiplied by the shoulder - the radius of the block R or the radius of the sleeve r.

The force of the incoming and outgoing rope arises as a result of the interaction and friction of the rope threads. Since the force for bending / unbending the cable is significantly less than the others, when calculating the effect on the axis of the block, this value is often neglected:

N \u003d 2 S run × sinα (2)

In this equation:

- N - impact on the pulley axis;

- S run - the effort from the side of the oncoming rope (taken approximately equal to S run;

- α is the angle of deviation from the axis.

Pulley block

Calculation of the unit efficiency

As you know, efficiency is the coefficient of efficiency, that is, how effective the work performed was. It is calculated as the ratio of completed and spent work. In the case of a pulley block, the formula is applied:

ηb \u003d S run / S run \u003d 1 / (1 + q + 2fsinα × d / D) (3)

In the equation:

- 3 ηb - unit efficiency;

- d and D - respectively, the diameter of the bushing and the pulley itself;

- q - coefficient of rigidity of the flexible connection (rope); f is the coefficient of friction;

- α is the angle of deviation from the axis.

It can be seen from this formula that the efficiency is influenced by the structure of the block (through the coefficient f), its size (through the ratio d / D) and the rope material (coefficient q). The maximum value of efficiency can be obtained using bronze bushings and rolling bearings (up to 98%). Plain bearings provide up to 96% efficiency.

The diagram shows all the forces S on different branches of the rope

The lifting mechanism consists of several blocks. The total efficiency of the chain hoist is not equal to the arithmetic sum of all the individual components. For the calculation, a much more complex formula is used, or rather, a system of equations, where all forces are expressed through the value of the primary S0 and the efficiency of the mechanism:

- S1 \u003d ηп S0;

- S2 \u003d (ηп) 2 S0; (- 4)

S3 \u003d (ηп) 3 S0; ….

- Sn \u003d (ηп) n S0.

Efficiency of the chain hoist at different multiplicity

Since the efficiency is always less than 1, with each new block and equation in the system, the value of Sn will rapidly decrease. The total efficiency of the chain hoist will depend not only on ηb, but also on the number of these blocks - the multiplicity of the system. According to the table, ηп can be found for systems with a different number of units at different values \u200b\u200bof the efficiency of each.

How to make a lift with your own hands

In construction, during installation work, it is far from always possible to fit a crane. Then the question arises how to lift the load with the rope. And here a simple pulley block finds its application. For its manufacture and full-fledged work, you need to make calculations, drawings, choose the right rope and blocks.

Different schemes of simple and complex lifts

Base preparation - diagram and drawing

Before proceeding with the construction of a chain hoist with your own hands, you need to carefully study the drawings and choose a scheme suitable for yourself. You should rely on how it will be more convenient for you to place the structure, what blocks and cable are available.

It happens that the carrying capacity of the pulley blocks is not enough, and there is no time and opportunity to build a complex multiple lifting mechanism. Then they use double pulley blocks, which are a combination of two single ones. This device can also be used to lift a load so that it moves strictly vertically, without distortions.

Dual model drawings in different variations

How to find a rope and a block

The most important role in building a chain hoist with your own hands is played by a rope. It is important that it does not stretch. These ropes are called static ropes. Stretching and deformation of the flexible connection causes serious losses in work efficiency. For a homemade mechanism, a synthetic cable is suitable, the thickness depends on the weight of the load.

The material and quality of the blocks are indicators that will provide the calculated lifting capacity to the self-made lifting devices. Depending on the bearings that are installed in the block, its efficiency changes and this is already taken into account in the calculations.

But how to raise a load to a height with your own hands and not drop it? To secure the load from possible reverse movement, you can install a special fixing block that allows the rope to move in only one - the desired direction.

The roller along which the rope moves

Step-by-step instructions for lifting a load through a block

When the rope and blocks are ready, the scheme is selected, and the calculation is made, you can start assembling. For a simple double chain hoist you will need:

- roller - 2 pcs.;

- bearings;

- bushing - 2 pcs .;

- holder for the block - 2 pcs .;

- rope; load suspension hook;

- slings - if they are needed for installation.

For quick connection, use carbines

Step-by-step lifting of the load to a height is carried out as follows:

1. Connect the rollers, bushing and bearings. Combine it all into a cage. Get a block.

2. The rope is launched into the first block;

3. The holder with this block is rigidly attached to a fixed support (reinforced concrete beam, pillar, wall, specially mounted stem, etc.);

4. Then the end of the rope is passed through the second block (movable).

5. A hook is attached to the holder.

6. Fix the free end of the rope.

7. Sling the load to be lifted and connect it to the chain hoist.

A homemade hoist is ready-to-use and will give you double the power win. Now, to raise the load to a height, it is enough to pull on the end of the rope. By bending around both rollers, the rope will lift the load effortlessly.

Is it possible to combine a chain hoist and a winch

If you connect an electric winch to the homemade mechanism that you build according to this instruction, you get a real do-it-yourself crane. Now you don't have to strain at all to lift the load, the winch will do everything for you.

Even a hand winch will make lifting a load more comfortable - no need to wash your hands on the rope and worry about the rope slipping out of your hands. In any case, turning the winch handle is much easier.

Winch polyspast

In principle, even outside the construction site, the ability to build an elementary chain hoist for a winch in field conditions with a minimum of tools and materials is a very useful skill. It will be especially appreciated by motorists who were lucky enough to get stuck in a car somewhere in an impassable place. A hastily made chain hoist will significantly increase the productivity of the winch.

It is difficult to overestimate the importance of the chain hoist in the development of modern construction and mechanical engineering. Everyone should understand the principle of operation and visually imagine its design. Now you are not afraid of situations when you need to lift a load, but there is no special equipment. A few pulleys, rope and ingenuity make it unnecessary to use a crane.

Polyspast is a system of movable and fixed blocks connected by flexible ties (ropes, chains) used to increase the force or speed of lifting loads. A chain hoist is used in cases where it is necessary to lift or move a heavy load with minimal effort, provide tension, etc. The simplest chain hoist consists of only one block and a rope, while it allows to halve the tractive effort required to lift the load.

Usually, power pulleys are used in lifting mechanisms, which allow reducing the rope tension, the moment from the weight of the load on the drum and the gear ratio of the mechanism (hoists, winches). High-speed pulley blocks, allowing you to get a gain in the speed of moving the load at low speeds of the drive element. They are used much less frequently and are used in hydraulic or pneumatic lifts, loaders, mechanisms for extending telescopic booms of cranes.

The main characteristic of the chain hoist is the multiplicity. This is the ratio of the number of branches of the flexible body, on which the load is suspended, to the number of branches wound on the drum (for power pulley blocks), or the ratio of the speed of the leading end of the flexible body to the driven one (for high-speed pulley blocks). Relatively speaking, the multiplicity is the theoretically calculated coefficient of gain in strength or speed when using a chain hoist. Changing the multiplicity of the chain hoist occurs by introducing or removing additional blocks from the system, while the end of the rope, with an even multiplicity, is attached to a fixed element of the structure, and with an odd multiplicity, on a hook cage.

Depending on the number of rope branches attached to the drum of the hoisting mechanism, single (simple) and double pulley blocks can be distinguished. In single chain hoists, when winding or unwinding a flexible element due to its movement along the axis of the drum, an undesirable change in the load on the drum supports is created. Also, if there are no free blocks in the system (the rope from the hook block goes directly to the drum), the load moves not only in the vertical, but also in the horizontal plane.

To ensure a strictly vertical lifting of the load, double chain hoists (consisting of two single ones) are used, in this case both ends of the rope are fixed on the drum. To ensure the normal position of the hook suspension with an uneven stretching of the flexible element of both pulleys, a balancer or equalizing blocks are used. Such pulley blocks are used mainly in bridge and gantry cranes, as well as in heavy tower cranes in order to be able to use two standard cargo winches instead of one large-sized high power, as well as to obtain two or three lifting speeds.

In power pulley blocks, with an increase in frequency, it is possible to use ropes of reduced diameter, and as a result, to reduce the diameter of the drum and blocks, to reduce the weight and dimensions of the system as a whole. Increasing the multiplicity allows to reduce the gear ratio of the gearbox, but at the same time requires a longer rope length and rope capacity of the drum.

High-speed pulley blocks differ from power pulleys in that in them the labor force, usually developed by a hydraulic or pneumatic cylinder, is applied to the movable cage, and the load is suspended from the free end of the rope or chain. The gain in speed when using such a chain hoist is obtained as a result of an increase in the lifting height of the load.

When using pulley blocks, it should be borne in mind that the elements used in the system are not absolutely flexible bodies, but have a certain stiffness, therefore the oncoming branch does not immediately fall into the block stream, and the running branch does not immediately straighten. This is most noticeable when using steel ropes.

Once upon a time, timber was a working option for building my house. And calculating the savings, I worked out various options, including how to assemble a wooden house alone. Of course, this is not very convenient, but the budget was very limited. I abandoned the "zakidnyak" technology, therefore, thinking about the lifting device, I was looking for suitable solutions around and on the Internet.

One person can lift logs of 100-150 kg using simple devices. And if there are forest trees and a crane on the site, it is difficult to do without such devices.

For example, a man assembled this log house completely alone. At the same time, he did not rearrange the crane, he stood all the time in one place.