Construction and device chainsaws

A chainsaw refers to devices that work with an internal combustion engine. In such devices used a single cylinder engine that runs on gasoline. The gasoline tool does not have a reducer, there is only a single-stage chain drive that drives the saw chain.

Chainsaw job

The chainsaw is necessary for quick and easy cutting of wood of any size.

The chainsaw has a simple design, but this device is reliable and capable of ensuring uninterrupted operation in harsh conditions.

This design consists of a large number of elements, including the air cleaning system fed into the carburetor, a tire with a chain, a chain tensioner and others.

More about each of the elements of the chainsaw

Diagram of a two-stroke two-stroke piston engine

Scheme of a two-stroke engine with a piston of double diameter.

In the most common chainsaws used two-stroke engine with one cylinder. It works together with a flywheel, a special coupling, an ignition element and a sleeve to fix the structure. The similar engine has turns about 13000 rpm. In this regard, there are high demands on the oil, which is added to the mixture of fuel.

The chainsaw is equipped with a centrifugal clutch, which works automatically depending on the number of revolutions of the engine. At low speeds, elements with special linings that are free in the radial direction will be attracted to the central part of the shaft by springs and will not transmit rotation to the drum, which is connected to the star from the chain. When the engine speed reaches the values ​​at which the centrifugal force exceeds the reinforcement of the springs, the pads will be pressed against the outer base of the drum and will start to scroll. After that, the leading star will start to scroll, which drives the chain. The star is located behind the clutch or from the outside of the latter.

The main advantage of couplings of this type is that, in the event of a chain jamming, the grip of the gas powered tool will slip without stopping the engine and without creating malfunctions of devices that transmit movement from the engine to the chain.

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Read more about the ignition system and the carburetor

Two-stroke engine workflow

Two-stroke engine workflow.

Contact ignition, which was previously used in devices equipped with gasoline engines, is no longer in demand. Designs from the best manufacturers are equipped with electronic ignition, which saves users from the hard work of adjusting the gap in the contacts and their constant cleaning.

The modern ignition system consists of the following elements:

  • flywheel;
  • ignition system with electrical circuit;
  • candle;
  • high voltage drive.

The flywheel will rotate and initiate the electromotive force in the module, which is converted by the electrical circuit into the necessary signals. Similar signals are then given to the candle. A spark will appear between the contacts, which will ignite the mixture.

Chainsaw carburetor

The carburetor chainsaw is necessary to ensure the smooth operation of the engine.

The carburetor is an important element of the power tool. Together with the ignition, he will be able to ensure the smooth operation of the engine. With it, you can prepare the air-fuel mixture, the quality of which will depend on the ease of launch, power and uninterrupted operation of the gasoline-powered tool. Most often, manufacturers of such saws use carburetors of the most common brands.

In the carburetor there is a damper that allows you to impoverish or enrich the mixture depending on the working conditions. To make fine tuning, you should use several screws, with the help of which the engine revolutions and idling are adjusted. At the top of the carburetor installed air filter that cleans the incoming air.

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Chainsaw Fuel System

In the simplest version, the fuel system consists of a tank with a volume of about 0.5 liters, a fuel filter and a hose through which the fuel will be delivered to the carburetor. A similar volume of the tank is enough for about 35-40 minutes, if we consider that the power of the chainsaw is 2 kW and the fuel consumption is no more than 1.2 l / h. Such an expense will be obtained at the maximum load on the structure.

Chainsaw fuel system

Fuel system for chainsaws: 1 - fuel filter, 2 - carburetor, 3 - manual pre-priming pump.

In order to fill the tank with air and not to create negative pressure in the process of fuel consumption, a breather is made in the lid that closes the opening. If this gadget becomes clogged with dirt, then the gas powered tool stalls. You should know that when the pressure of the fuel can not get into the carburetor.

From the tank, the fuel will be pumped out through a hose, which is loose in the tank. Its free movement is ensured so that the hose is always in the tank. A filter is attached to the input element. The fuel will be pumped by the pumping structure inside the carburetor.

To facilitate the launch, some chainsaw designs are equipped with mechanical pre-pumping pumps — primers. In the case of starting a gasoline-powered instrument with a primer, the carburetor will first of all be filled with fuel, and the excess of the latter will flow back into the tank. As a result, the engine will start faster, as the carburetor will be filled with fuel. If there is no primer, the carburetor will be filled with fuel using a starter.

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Air cleaning system

Chainsaw air cleaning system

Chainsaw air cleaning system.

In the process, the engine gasoline tools uses the mixture that is formed in the carburetor. To prevent dirty air from entering the structure, it should be cleaned with filters. Such filters may consist of several elements. The snow filter will prevent the penetration of snow into the air cleaning system, it is used only in the winter period. At high temperatures, the structure should be removed.

In some cases, the air is cleaned using centrifugal forces. The air flow is twisted by the impeller of the flywheel, after which the impurities recline from the retractor nozzle, which leads to the installed filter. Filters of this type can be made of special foam rubber, nets of nylon and other materials.

In the process of gasoline tools in the air in the area of ​​its action may be contaminated with sawdust. Too much contamination of the filter media can reduce the amount of air that enters the carburetor. This can lead to enrichment of the mixture and reduce the power of gasoline tools. That is why the filter must be constantly cleaned. Cleaning should be done not only when disassembling a tool for the purpose of repair, but more often. After each long-term work, it is recommended to clean the structure. The cleaning method will depend on the material used to make the filter: in most cases blowing or flushing is used.

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Starter tool

Chainsaw starter device

The device is a chainsaw starter.

A similar element is used to start the design by turning the shaft. The mixture that is fed to the engine will compress between the piston and the cylinder head. Such a mixture is ignited in the event of a spark, as a result of which the engine is turned on.

The starter consists of such details as:

  • drum;
  • cable;
  • lever;
  • return spring.

If you dramatically pull the handle up, the ratchet of the drum will catch on with the teeth, which are located on the shaft. After this, the crankshaft will roll. If you release the handle, the return spring will return it to its initial position.

To crank the shaft at the speed at which the engine starts, it will take some effort. In almost all cases, it is impossible to launch the gas powered tool from the first time, so it will be necessary to pull the handle many times. To facilitate the launch, you can use various methods. For example, you can enrich the mixture of fuel with a special valve or reduce the pressure in the cylinder with a special valve. The valve can be made automatically to twist in the event of an increase in pressure in the cylinder, which will occur during the ignition of the fuel. In the design of the starter may be a spare spring, which in the case of pulling the cable will first be compressed, then sharply razmozhmesya, spinning the motor.

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Chain of gasoline tools

Saw chain structure

The structure of the chain saw.

The chain consists of links for cutting, shanks and fixing elements. In a single design, all components are assembled with rivets.

The main and most complex links of the chain are cutting tools, which can be divided into right and left. The upper part of the clove has the greatest width. It is able to provide a wide width cut, which eliminates the jamming of other links.

The shape of the teeth for cutting can vary greatly among chains of different manufacturers. In most cases, you can see the chipping and chisel shape, but there are other forms of incisors.

The edges of the teeth for cutting are sharpened at a specific angle. If a longitudinal chain is used, the angle will be 10 °. If the chain is used for cross-cutting, the angle is 30 °. It is worth noting that longitudinal chains are rarely used. If necessary, longitudinal cuts can be performed using a chain of transverse sawing.

Chainsaw Chain Pitch

Step chain benzpily.

The main characteristic of the chain is its step. To establish the pitch of the chain, it is necessary to measure the gap between the central parts of the first and third fixing rivets. The result obtained should be divided by 2. Thus, the chain pitch in mm can be obtained. However, most often the step is indicated in inches. The gap between the central parts of such fixing rivets should be measured because the gaps between the openings of the links may have a different size. The most commonly used chain in increments of 0.325 and 3/8 inches. The first chains are used in low power engines. High power chainsaws come complete with a 0.4 inch chain. In the case of using a chain with a small link thickness and a small step, you can get a clean and high-quality cut.

The important parameters include the thickness of the shank. The most commonly used chains with a shank thickness of 1.3 mm. They are often used on both ordinary and specialized gas powered tools. The thickness of the links must be matched to the width of the gap of the guide rail; the chain for sawing must be exactly the same as the guide rail.

Chain manufacturers use different production technologies and materials. When choosing a material, one should pay attention not to hardness, since hard teeth are hard to sharpen manually. The main characteristics are viscosity and impact strength, as they can be used to determine the durability of the structure. In the process of manufacturing cutting teeth wear-resistant alloy steel is most often used. Quite often, the cutters are chrome-plated so that it is possible to increase the hardness of the surface. Some manufacturers use shot blasting to increase the viscosity of the teeth.

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Gasoline Tires

The main parameters of the chainsaw tires

The main parameters of the chainsaw tires.

The tire is an important design of the chainsaw. It is used as a guide for the chain. In the process, the tire will be subjected to significant loads, because it should be made of a viscous metal of good quality, which has a high elasticity.

To drive a chain, the tire must have a guide gap through the holes in which the links of the chain will move. The groove gap will also serve as a channel that supplies the oil for processing the chain. The main parameters of the tire include:

  1. The dimensions of the fixed holes, which will depend on the type of gas powered tools.
  2. The width of the gap, which corresponds to the thickness of the shank of the chain. The width of the tire gap is 0.02-0.05 mm greater than the thickness of the chain links. In this way, precise lateral chain management can be achieved.
  3. Star pitch, which determines the compatibility of the applied chains and tires.
  4. The length of the cut, which determines the dimensions of the material being processed.
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Chainsaw Chain Brake

Chainsaw design with inertial chain brake

Chainsaw design with inertial chain brake.

The characteristics of chainsaws include an open cutting element in the form of a tire with a chain that runs along it. Such a tire can pose a considerable danger to the work item. Therefore, the device gasoline tools must provide appropriate security measures. The chain brake is designed to quickly stop the chain in the event of a kickback, which sometimes occurs when the scrolling chain accidentally touches it. As a result, the tire can get a sharp blow, which will throw it to the side or up. In this case, it will hurt the user spinning chain. To avoid this, a similar tool must be equipped with a braking structure that stops the chain from rotating in the event of a back kick.

The start of the brake element can be contact or inertial. The first will occur in the case of pressing the brake stop, which may occur in the process of discarding the tool. In this case, the displacement of the stop can lead to a tightening of the brake band, as a result of which the working chain will stop.

The inertial launch of the brake element is based on the inertial forces arising in the event of a sharp blow to the tire, which act on the elements of the brake system. Ultimately, the same result will be obtained as in the previous case, tightening the tape and stopping the working chain. Inertial launch of the brake element will occur faster than the contact.

Preparatory work and assembly of gasoline tools after repair should be completed by checking the brake system of the chain. If the brake element does not work, the saw is defective.

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Chainsaw chain lubrication system

Circuit check circuit lubrication

Scheme of testing the operation of the chain lubrication system

Lubrication of the chain and tires in gas powered tools is performed automatically. Oil will be poured into the appropriate container, after which, by a special design, it will fall into the pumping device, which is installed from the side of the working chain. From the pump design, the oil will flow into the tire gap, and then proceed to the chain itself.

Oil pumping devices are driven by a gear that is driven by a driving star. While the engine is idling, no oil will be supplied to the system. The performance of the pump design will depend on the number of revolutions of the working star. The higher the revolutions, the more oil will flow to the chain. Some designs are equipped with a manual performance adjustment system.

A chainsaw is a complex mechanism, so it is recommended that you familiarize yourself with its construction before work.

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