What A Chainsaw Consists Of
Chainsaw device with additional features
When choosing a tool, you need to pay attention to weight, power, the presence of protective devices and auxiliary parts.
Vibration protection and start assistance
The fluctuations that occur during operation have a very strong impact on human health. In particular, the joints suffer. Anti-vibration system keeps you healthy and improves working comfort.
The start system allows you to stop the chainsaw for certain periods of time and simply start it as needed. It helps a lot when you often have to move between trees.
In the main, chainsaws do not need additional settings. But from time to time, adjusting screws and levers are used to improve performance. They are needed to establish good working speed.
Chainsaw Stihl MS 180-16
This option includes a 16-inch tire. Due to this, when assembled, the Stihl MS 180 chainsaw has large dimensions. Suitable for felling trees up to 30 cm in diameter.
Chainsaw chain Stihl 180
The Stihl 180 saw chain deteriorates during long interruptions. To avoid this, it must be stored in an oil bath. The manufacturer for this type of Stihl 180 saws recommended Stihl chains with parameters 3/8″ by 1.3 mm. Size 12 is allowed″, fourteen″ and 16″.
The main types of saws include 3 types:
- Household. They have an ordinary design and are designed for light work. For example, cutting down a small tree in your own area. Low weight and comfortable design.
- Semi-professional. They have a huge area of implementation, but cannot be used once a day for 810 hours. often they cut knots in logging.
- Prof. The most powerful tool designed to work every day for 1016 hours a day throughout the year. They are made from sturdy materials and are used for felling.
The stihl ms 180 chainsaw has a fairly simple design, designed to be serviced by users without a certain experience. The saw carburetor is designed in such a way that it cannot be adjusted to the maximum engine speed. The only available adjusting screw, is responsible for stable idling.
The stihl ms 180 chainsaw consists of the following structural elements:
- Flywheel, it is also a cooling fan;
- Ignition module;
- Saw chain brake mechanism;
- Air filter with replaceable filter element;
- Oil and fuel tanks;
- Side cover with chain tension adjustment mechanism;
- Control handle and saw handle.
Consider the device of a chainsaw, and how the main elements work in more detail.
Pull the starter cord to start the engine.
The starter transmits force through the flywheel to the crankshaft and drives the piston. At this moment, under the action of an air pulse from the engine crankcase, which flows through special channels to the carburetor, the fuel pump starts supplying gasoline with oil to the carburetor, where an air-fuel mixture is formed and supplied under the piston.
At the same time, at the moment the piston is at TDC (top dead center), an electrical discharge is supplied from the ignition coil to the spark plug, which ignites the fuel mixture under the piston in the cylinder and forces the piston to move downward, thereby making a working stroke.
After a successful start, the saw repeats all work processes cyclically and works stably.
Consider how the power from the engine is transmitted to the drive sprocket and causes it to twist the saw chain. For this, the stihl ms 180 chainsaw has a centrifugal clutch that is installed inside the drive sprocket and is rigidly attached to the engine crankshaft.
With an increase in engine speed, the clutch is released and, resting on the sprocket housing, transfers to it the force from the engine crankshaft, forcing it to rotate the chain mechanism.
The next element of the Stihl 180 chainsaw is the chain brake. The brake device is quite simple and consists of a control lever and a metal plate that wraps around the drive sprocket and is installed in the saw body. In working position, the chain brake plate securely holds the sprocket drum.
The chainsaw engine has a maximum speed of about 13,500 rpm. This imposes strict requirements on the oil added to the fuel mixture.
Why is a chainsaw carburetor called a diaphragm
Before proceeding to consider the principle of operation of a chainsaw carburetor, you need to figure out why they are called membrane. The diaphragm (diaphragm carburetor) is an advanced model that can work in any position. This is very important, as a chainsaw, like lawn mowers, is not operated in one position. Therefore, membrane carburetors are capable of working in any position, which is their main difference from devices of an outdated design or an old model.
If a membrane is used in the carburetor of the new model, then in the models of the old model, which are used on a chainsaw such as Druzhba, there is a float chamber. It is in the float chamber that gasoline of the corresponding volume accumulates. When the float goes down when gasoline is consumed (the chamber is emptied), the needle moves along with the float, which opens the fuel supply hole to the float chamber.
In this case, the normal operation of the old-style carburetor is ensured under one simple condition, it must be in the appropriate position. When the device is moved to the side 90 degrees or more, the float will move, and therefore the needle will block the fuel holes. That is why old-style chainsaws are designed only for operation in one position. The unit itself is in one position, and depending on the type of work performed (cutting down a tree or sawing a log), the position of the tire is adjusted.
Knowing how the Druzhba chainsaw works, you can begin to consider the principle of operation of the carburetor of modern units, in which there is no mechanism for moving the tire (changing the angle of its position).
How does a chainsaw carburetor work?
The principle of operation of the chainsaw carburetor also includes the supply of an air mixture to the device. As you understand, it is not clean fuel (oil with gasoline) that enters the combustion chamber, but a fuel mixture of oil with gasoline from the tank and air that passes through the filter element.
So, the air passes through the filter, and enters the device through the membrane number 7.
The air damper 7 during cold start is almost completely closed, as shown in the diagram. Through it there is a slight intake of air into the system. Air enters the diffuser 16. Number 12 denotes the idle and medium speed channels or jets. These channels are interdependent, that is, the medium speed channel is transitional from idle. These channels are constantly open, so fuel in an appropriate dosage enters the diffuser, where it mixes with air, heading towards the cylinder.
Number 15 denotes the maximum speed channel, which consists of a valve with a rubber base. This valve supplies fuel in one direction to the diffuser chamber. Further, the throttle valve 8 enters the system, the movement of which depends on the force of pressing the gas unit. When starting, valve 8 is in a vertical position, so the chainsaw operates only on the fuel mixture coming from channel XX. At the same time, the amount of air is insignificant, since the damper 7 is also open a few millimeters. When the trigger of the tool is pressed, the flap is deflected by 10-15 degrees, as a result of which the fuel mixture is supplied from the medium speed channel 12 in the diagram above.
When the sawman starts sawing wood, the number of revolutions increases to the maximum, so the shutter moves up to 90 degrees from the initial position. There is an increase in the amount of fuel, which contributes to the acceleration of the combustion of the fuel mixture.
In order to fill the chamber 14 with a fuel mixture of gasoline and oil, which enters through the channel closed by the needle, it is necessary to create a vacuum, due to which the membrane 13 is pulled inward, thereby acting on the stem. The vacuum in the chamber 14 is created during the jerking of the starter handle when the tool crankshaft moves. The piston moves up and down when the starter handle is blinked or poked, which provokes the creation of pressure inside the chamber 14. As a result, the chamber is filled with fuel, which flows through the corresponding channels into the diffuser, mixing with air, and heading into the cylinder.
After the engine of the unit is started, the piston will begin to move under the influence of the combustible mixture, therefore, the vacuum in the chamber is formed constantly, which actually provokes the deflection of the plate 13, which acts on the needle valve through which fuel enters the main chamber of the carburetor of the chainsaw.
Actually, this is the principle of operation of a membrane-type chainsaw carburetor, the functioning of which does not depend in any way on the angle of its location. Knowing the design and principle of operation of the unit, you can start setting up, cleaning and adjusting.
How does the carburetor work on a chainsaw, we deal with the fuel supply to the device
So, the device under consideration on a modern chainsaw has a simple principle of operation, which is based on vacuum. Probably, when repairing a chainsaw, more than once every sawyer asked himself the question why there was no fuel pump on the unit. On such a small unit, there is simply no place to install a pump, and the carburetor itself performs its fuel supply function. To understand how the chainsaw carburetor works, let’s first consider the features of the fuel supply to the mechanism.
How is fuel supplied in modern chainsaws with membrane carburetors? In modern chainsaws, fuel is supplied to the carburetor through a special membrane, which is indicated in the diagram below under the number 4.
In the diagram, this membrane is indicated as a dotted oval. Its movement occurs due to the vacuum pressure. A quite pertinent question arises as to where this rarefaction comes from. Let’s consider in detail why we will rely on the diagram below.
The fitting at number 1 is connected to the gas tank, which is located below the level of the carburetor. According to the law of physics, fuel cannot enter the carburetor according to such a scheme. For this, in the design of the device under consideration, there is a fitting 2 (it can also be represented as a hole, which depends on the model of the tool, but the principle of operation of the chainsaw carburetor is identical). Through fitting 2, pressure enters the carburetor, the intake of which takes place through the channel from the KShM chamber (crank mechanism). The diagram is shown in black line.
From the KShM chamber to the carburetor chamber through the nozzle 2, there is an alternating supply of air under pressure, the cycle of which depends on the speed of rotation of the tool crankshaft. That is why, before starting the chainsaw, you need to initially make several movements of the starter (which drives the crankshaft) without ignition, in order to pump gasoline into the combustion chamber, and only after that start.
When a vacuum pressure is created by membrane 4, valve 3 is opened and closed alternately. Fuel enters the carburetor chamber and is directed to the inlet valve number 5. Valve 5 opens depending on the pressure generated, but not by the membrane, but by the fuel itself. Further, the fuel enters through the filter element number 6, and moves already cleaned up to the needle. The further scheme of operation of the chainsaw carburetor is described in the next section.
What does a chainsaw carburetor consist of?
The considered units of modern chainsaws differ in design from the old-style devices. over, this difference lies not only in the design, but also in the principle of action. But first things first. First, we will find out the main components of the mechanism, and then we will understand the principle of the functioning of the chainsaw carburetor.
Structurally, the chainsaw carburetor can be divided into three parts:
- Fuel suction chamber from the gas tank. This chamber is connected not only with the gas tank through the fuel line, but also with the design of the crank mechanism. This part consists of two fittings, a membrane for pumping fuel, two valves, a filter and a transport channel.
- The chamber for the accumulation of the fuel mixture and its flow to the idle, medium speed and maximum speed channels. This chamber consists of a needle or needle valve, a diaphragm for opening the needle, a fuel accumulation chamber, adjusting screws, a maximum speed flap, and XX and medium speed channels, which are always open
- The working area is the main area in which air and fuel mix and flow into the combustion chamber. The main working elements of the working area include dampers (air and throttle), as well as a diffuser, in which fuel and air are mixed
The principle of functioning of the carburetor on a two-stroke engine of a chainsaw
We continue to understand step by step with the principle of operation of the carburetor of two-stroke engines of chainsaws. Such knowledge will be useful not only for beginners, but also for those who wish to independently repair, adjust or adjust the carburetor. It is also necessary to know the principle of operation in order to understand why certain defects arise in the operation of the instrument.
So, the fuel passes through the filter element, and reaches the needle, which is indicated in the diagram below as number 11.
Now we have to figure out the principle of operation of the second membrane of the carburetor, which is shown in the diagram at number 13. Under the membrane is a protective plate with an opening through which air enters. The diagram below shows air movement.
Number 14 on the diagram shows the fuel in the carburetor chamber. However, it will not enter this chamber until the needle 11 opens (moves down). To move the needle, a membrane 13 is used, which is connected to the needle through a rocker arm. The spring mechanism near the rocker arm is designed to return the membrane 13 to its original position.
It is worth noting that the membrane is made of a flexible material, so it bends under the influence of the rod from the rocker arm. To open the needle, the membrane must move upward, thereby acting on the stem, and through the rocker arm, the needle moves to the lower position, which will entail the flow of fuel into the chamber.
To understand why the membrane 13 bends or moves, due to which the needle opens for fuel to enter the chamber, it will also be necessary to find out the features of air flow into the mechanism.
How a chainsaw carburetor works detailed description
Many people know how a two-stroke carburetor works on tools such as chainsaws, lawn mowers, and gas generators. However, this knowledge is only generalized, and when it becomes necessary to repair or regulate the carburetor, a bunch of questions immediately appear, the answers to which can be found yourself, if you understand thoroughly what the principle of the chainsaw carburetor is based on. It is in this that you have to figure out how the carburetor of chainsaws of different brands works.
Below is a diagram of another chainsaw carburetor.
Carburettors have a throttle valve that allows the mixture to be leaner or richer, depending on the operating conditions. For fine tuning, there are several screws with which to adjust the low and high engine speed, as well as idle speed. An air filter is installed on top of the carburetor, which cleans the air entering it.
Chain tensioning mechanism
For added convenience, the chain tensioning screw can be located on the side.
The chainsaw engine has a maximum speed of about 13,500 rpm. This imposes strict requirements on the oil added to the fuel mixture.
At low speeds, elements with friction linings (1), having a degree of freedom in the radial direction, are attracted to the center of the shaft by springs (2) and do not transfer rotation to the drum (3) connected to the sprocket of the driving chain. When the engine speed of the chainsaw reaches values at which the centrifugal force exceeds the force of the springs, the friction segments are pressed against the inner surface of the drum and begin to rotate it. As a result, the drive sprocket starts to rotate, which drives the saw chain.
As you can see in the photo, the sprocket is behind the clutch.
On other chainsaws, the sprocket may be on the outside of the clutch.
The main advantage of clutches of this type is that when the chain is jammed, the chainsaw clutch slips without muffling the engine and without causing breakdown of the mechanisms that transmit movement from the engine to the chain.
The starter mechanism consists of a drum (1) with a cable (2) and a handle (3), and a frame (4) with a return spring. When the handle is pulled up sharply, the drum ratchet engages the teeth on the engine shaft and turns the crankshaft. When the handle is released, the return spring returns it to its original position.
It takes a certain amount of force to turn the crankshaft at the speed at which the engine starts. It often fails to start the chainsaw with one jerk, you have to pull it several times. Various methods are used to facilitate starting. Enrichment of the fuel mixture using the carburetor flap, or reducing the pressure in the cylinder using a decompression valve (to facilitate crankshaft cranking). The valve is made to automatically close when the pressure in the cylinder rises when the mixture is ignited. Sometimes an additional spring is used in the starter mechanism, which, when the cable is pulled out, is first compressed, and then abruptly unclenched, spinning the motor.
The main and most complex chain links are cutting links, which are subdivided into right-handed and left-handed. Top edge of the tooth. The widest of all elements. It provides a wide kerf to prevent the remaining links from getting stuck.
The shape of the cutting teeth can vary significantly from chain to manufacturer. There are two main forms. Chipper (a) and chisel (b). However, there are also different intermediate contours of the incisors.
Tooth cutting edges. Side and top. Sharpened at a specific angle. For rip sawing chains, it is 10, for crosscut. 30. Rip sawing chains are rarely used. If necessary, rip sawing can also be done with a cross saw chain. Read more about chainsaw sharpening angles in the article Chainsaw chain sharpening.
The main characteristic of a chain is its pitch. To establish the chain pitch, measure the distance between the midpoints of the first and third rivet rivets (see figure below) and halve this dimension. The result obtained. Chain pitch in mm. However, in most cases, the chain pitch is given in inches. The distance between the centers of the first and third rivet rivets is measured because the distances between the holes of the driving links and the cutting links or connecting links can vary in magnitude. The most common chains are 0.325 and 3/8 inch (8.255 and 9.525 mm, respectively). Chains with a pitch of 0.325 are used with low power engines (up to 40-50 cm 3), while powerful chainsaws are usually equipped with 0.404 inch chains (such chains have a higher performance). The cut is cleaner and more accurate when sawing using a chain with a smaller link thickness and a smaller pitch.
Shank thickness is an important characteristic. There are five standard thicknesses: 1.1, 1.3, 1.5, 1.6 and 2 mm. The most common chains are 1.3 mm (0.05 “) shank. They are widely used on both household and professional chainsaws. The thickness of the drive links must be matched to the width of the guide bar groove so that the saw chain fits perfectly on the guide bar.
Chain manufacturers use different technologies to make them and use different materials. The defining characteristic of the latter is not hardness (teeth that are too hard do not lend themselves well to manual sharpening), but toughness and impact resistance. It is they who determine the durability of the chain. Therefore, wear-resistant alloy steels are used in the manufacture of cutting teeth. Cutters are often chrome plated to increase surface hardness. Some firms use shot blasting to increase the toughness of the teeth.
To guide the chain, the tire has a guide groove on its periphery, in which the driving links of the chain move. The groove of the groove also serves as a channel for supplying oil for lubricating the chain. The main parameters of the tire include:
- Dimensions of connecting holes (a), depending on the type of chainsaw.
- The width of the groove (b), which should correspond to the thickness of the shanks of the chain used. The groove width of the bar is only a few hundredths of a millimeter wider than the thickness of the drive links of the respective saw chains. This enables precise lateral guidance of the saw chain.
- The pitch of the end sprocket (c), which also determines the compatibility of the used chains with the bus.
- Cut length (g), which determines the size of the material to be cut. Tree trunk diameter, etc.
The activation of the chain brake can be contact and inertial. The first occurs when the brake stop (1) is pressed on the worker’s hand, which occurs spontaneously when the saw is thrown back. The resulting displacement of the stop leads to the tightening of the brake band (2) on the clutch drum and to its stop, as a result of which the saw chain also stops.
The inertial brake engagement is based on the inertial forces arising from a sharp impact on the tire and acting on the brake elements, which leads to the same result as in the first case. Tightening the brake band and stopping the chain. Inertial brake engagement is faster than contact engagement. However, the second is more reliable. Any preparation for work, as well as the assembly of the chainsaw after its repair or maintenance, should end with a check of the chain brake. If it does not fire, the saw should be considered defective.