Sharpen Chainsaw Chain Near Me

Signs of a dull chain and the consequences of further operation

The difficulty of working with a dull chainsaw should not be confused with the difficulty of sawing hardwood or heavily dried logs. In all these cases, the speed of the operation decreases, but a blunt tool has a certain behavior. signs by which one can judge the need for sharpening:

  • the chainsaw does not immediately bite into the trunk of the tree, as if grinding, moving from the point of contact;
  • during cutting of soft breeds, the tool sluggishly enters the thickness of the wood, you have to press on the tire;
  • shavings from large with characteristic elongated particles turn into small thyrsa, which very rarely crumbles;
  • the chain heats up quickly, there is an unpleasant smell of burning oil for lubricating the guide bar.

In addition to these alarms, always after hitting a chain on metal nails, wire or burying a chainsaw in the ground, you can be one hundred percent sure of the need for subsequent sharpening of cutting edges.

What can happen to the tool in the future if you ignore the problem? The most harmless thing is that it will be impossible to work with a chainsaw, in the end it will get bored and will force you to service the unit. But adherents of the saying “You don’t need to have power” can come to the following conclusion:

  • an extra load on the body, because, frankly, you have to put pressure on the tool so that it saws;
  • overconsumption of fuel up to 30%, which is explained by the need to go through a longer cycle of revolutions to achieve the same result;
  • accelerated wear of the tire and other parts of the chainsaw.

In addition to all these negative consequences of bluntness of the saw, there is a high probability of the chain jamming in the trunk and injury to the operator performing the work.

sharpen, chainsaw, chain

Chainsaw sharpening angles and tooth configuration

  • Base. the lower part of the tooth, which has holes for connection with the rest of the chain elements and during operation hides in the guide channel of the bar. It is this part that is lubricated.
  • A special stop is an element of the tooth structure that allows the cutter to remove only a certain thickness of wood chips in one pass. Thanks to him, the chain does not get stuck in the fibers, and the chainsaw does not wedge.
  • The so-called tooth scapula is a cutter consisting of vertical and horizontal working surfaces that form cutting edges.

Tooth blades, or cutting edges, must be sharpened at a specific angle, otherwise it will be difficult to achieve optimal sawing characteristics of the chain. The upper blade (horizontal) has the function of cutting the tooth into the wood and forming a groove. Side or end blade (vertical) helps to trim fibers from the side.

The most important thing when sharpening a chainsaw is to achieve the correct angle of the upper blade, which should be within 60-50 degrees. The angle of the end blade is maintained within 85-60 degrees. It is also worth adhering to the angle in the plan (sharpening angle), namely, what is clearly visible when you look at the chain link from above. it departs from the side edge along the front mowing line and should be 10-15 degrees.

The productivity of operations when sawing wood in the transverse direction increases if the angle of sharpening of the chainsaw chain is increased to the maximum possible and vice versa. Chains designed for longitudinal cutting of a tree trunk should be sharpened at an angle of approximately 10 degrees.

Under no circumstances should the depth gauge be touched once again: improper grinding can lead to vibration during tool operation. Its debugging is done according to a special template.

File types and tips for choosing

Following the rules, before choosing files for sharpening the chainsaw chain, the exact chain pitch is determined by the chain marking. Further, they adhere to the recommendations:

Step size File diameter, mm
0.25 2×2
0.325 2×2.4
0.375 2×2.6
0.404 2×2.75

There are saw chains where it is appropriate to use round files with a cross-sectional diameter of 2×1.6 mm.

With the correct selection of the tool for sharpening the teeth of a chainsaw, its protrusion above the surface of the horizontal edge of the tooth during the process will not exceed 1/5 of its own diameter, which can be a guideline when selecting a file when the chain pitch cannot be determined.

No Nonsense Guide to Chainsaw Sharpening. How To Sharpen A Chainsaw Properly. FarmCraft101

Stages of work for manual sharpening at home

  • The bar with the chain is fixed with a vice so that its upper line is in a horizontal position.
  • Take the shortest tooth as a reference point and mark it with a marker or nitro enamel.
  • The body of the round file is wound under the main cutting edge, pressing it to the corner along the entire mowing line and at the same time pressing the holder against the tooth surface. Thanks to the holder, the round file will automatically take the desired position, protruding in relation to the upper plane of the chainsaw tooth.
  • With confident, even movements away from you, without changing the feed angle, two or three times are filed along the beveled surface of the upper cutting edge.
  • Rotate the file along its axis so that the development of an abrasive surface does not occur, and repeat the operation until the tooth sharpens.
  • After that, using a chain sharpening template, check the height of the limiter and, if necessary, grind it with a flat file.
  • Then, through one tooth, the entire cycle of operations is repeated until they reach the originally marked tooth.
  • Turn the tire over with the opposite side and sharpen all the other teeth of the chainsaw through one.

3 ways to sharpen your chainsaw chain with your own hands

Learn how to sharpen your chainsaw chain properly at home using a file, angle grinder and machine. A detailed video of the do-it-yourself sharpening process. We will show you how to work correctly with tools and devices.

It is very convenient to work with a chainsaw. Despite the fact that the unit weighs 5–7 kilograms, or even more, when sawing a tree trunk into logs, you simply wonder how quickly this happens, and there is practically no fatigue. But then the moment comes when it is harder and harder for the tool blade to enter the wood. There is only one diagnosis. the saw is dull, so you need to sharpen the chainsaw chain.

Whoever comes across this for the first time is a little upset, because it is not clear whether to do it yourself or give the instrument to specialists in the workshop. And what is the general sharpening method? But in fact, there is nothing terrible here, and with knowledge, you can easily sharpen chainsaw chains with your own hands. The correct strategy for solving the issue in this case directly depends on the load of the unit.

If a chainsaw is used from time to time, several times a year, then it may not make sense to buy a special sharpening machine or accessories, it is easier to solve the problem by using the services of a service center. But if a chainsaw is a means of earning or there is a desire to master the sharpening process yourself, then you should definitely purchase a sharpener or a machine and manually carry out this simple manipulation of the chain. Let’s see below what the correct sharpening of the chainsaw chain is based on.

Than manual sharpening is inferior to machine

  • Difficulty keeping the required angle. You don’t need to think that you can sharpen the chainsaw chain with just one round file, for this operation you will need at least a special guide and a second flat file.
  • Low speed of the operation. It is necessary to fix the guide on the tooth, manipulate with a round file, check the gap of the limiter, if it is necessary to correct it with a flat file, and only then proceed to the next tooth.
  • The need for experience. Despite the various helpers for sharpening a chainsaw by hand, first of all you need to feel the process, and this requires some experience.

Sharpening the chain with an angle grinder

For the operation you will need:

  • angle grinder, preferably slightly powerful and large;
  • cutting wheel for metal of the corresponding diameter and thickness of 2-3 mm;
  • vise or clamp to firmly secure the angle grinder to the table.

The angle grinder is clamped in a vice so that the disc is located strictly vertically, without a protective cover, in the direction of the operator. Sparks must fly towards the operator, therefore protective clothing and goggles must be worn to work. The angle grinder is turned on and, observing the angle, each link of the chainsaw chain is sharpened by eye.

We strongly advise against using this method of sharpening the tool. It can be very traumatic. When the metal of the tooth overheats (blackening), the latter becomes more fragile.

General rules for sharpening chainsaw chains

Do-it-yourself chainsaw sharpening

The tooth of the chain planes the wood like a plane, and the thickness of the chips is adjusted by the height of the stopper.

Intense sawing will quickly dull the chain. Several sharpenings may be required within one day. The problem is aggravated by the fact that the tooth quickly dulls when it meets the ground. It is enough to hook the soil with the tire once or twice, and the work can be stopped. the shavings become fine and the saw stops digging into the wood.

The sooner dull teeth are sharpened, the less material needs to be removed during sharpening, as a result. the service life of the saw chain is longer. Determining the moment when sharpening is already required is quite simple. An important feature is the feed force. A properly sharpened chain is pulled into the cut with just a little pressure. If, on the contrary, the chainsaw is forced to cut by increased feed force, then the teeth are dull. A dull chain can also be recognized if only small chips fly out of the cut instead of coarse thick chips.

In this situation, the chainsaw must be sharpened urgently. Do not cut with a dull or defective saw chain. the consequence is high stress in the body, high cyclic load, poor cutting results. In addition, this means a decrease in productivity, high fuel consumption and increased wear of all parts of the chainsaw.

Chain sharpeners

The round file holder has a mowing line that can be positioned correctly in relation to the chain. The holder fits onto the sharpened tooth in accordance with the line orientation. In this case, the insert itself rests on the upper edge of the tooth and the depth gauge, and the file is located under the cutting edge.

The use of a holder ensures that the file will fit to the tooth at the correct height. There are different tool holders for different pitches of the saw chain. The correct choice of holder, combined with the correct file diameter, ensures that the file protrudes over the back of the tooth by 1/5 of its diameter. Use only special saw chain files.

Before sharpening the chainsaw chain, it is advisable to secure the bar. When sharpening, it is necessary, keeping the position of the holder and pressing the file to the sharpened edge, to make several (2-3) turning movements away from you. Do not try to press too hard on the file, the movements should be smooth and measured. Rotate the file regularly to avoid one-sided wear. All other teeth are sharpened in the same way. It is more convenient to first sharpen the teeth in one direction, then change the position and do the same with the teeth in the other direction.

When sharpening all teeth, do the same number of strokes with the file at the same pressure. This will result in the same tooth length. All cutting teeth must be of the same length. Different lengths of teeth cause uneven chain running and cracking. If the length of the teeth is not the same, all cutting teeth must be filed to the length of the shortest tooth.

After several sharpening of the cutting teeth, the depth gauge is ground. To do this, a template is superimposed on it so that the stopper falls into the slot, and the tip protruding from the slot is grinded with a flat file.

The principle of using another set for sharpening chainsaws does not differ from the first, although its design is different.

A round file is also used to sharpen the cutting tooth, and the depth gauge is used to sharpen the depth gauge. flat. A special template provides parameters for sharpening both cutting teeth and stops. In the first case, it is superimposed on the chain in such a way that it falls into its slots. The file, placed on the template and brought under the cutting edge, rests on the guide rollers. The direction of movement of the file must be parallel to the lateral edges of the template.

When sewing the stopper, the template is applied so that the stopper falls into the cut, next to which is written SOFT (for soft wood) or HARD (for hard wood). As in the case of the first device, the file is seamed with smooth, even movements of the flat file away from you.

Chain Teeth Parameters

To achieve optimal cutting properties, the tooth blades are given specific angles. The back of the tooth falling back at an angle forms the posterior angle of the upper blade. This angle is needed to cut the upper blade into the wood.

The backward tapering blade of the tooth forms the back angle of the end blade. This angle is needed for side cutting of the chips.

The edge of the end blade forms a rake angle with the sliding surface of the cutting link. Front angles for different types of chains vary from 60 to 85 °.

The back angle of the upper blade characterizes the backward tilt of the upper blade.

This angle is measured relative to the sliding plane of the cutting link and, depending on the type of saw chain, ranges from 50 ° to 60 °. The top blade is the main blade and the back corner of the top blade. this is the most important corner. The clearance angle of the upper blade is difficult to measure, and the correct value is obtained by observing other prescribed values.

The sharpening angle or entering angle is obtained by measuring from the top cutting edge at right angles to the guide bar.

The sharpening angle can be changed, depending on the application. Rule of thumb: the larger the sharpening angle, the higher the cutting performance when cutting non-frozen softwood. Reducing the angle of sharpening when cutting frozen and / or hard wood contributes to a smoother saw blade and less vibration. However, sharpening angles greater than 35 ° and less than 25 ° should be avoided (except for rip chains where this angle is 10 °).

The rake angle, sharpening angle and upper blade angle change when sharpening. These angles have a decisive influence on the cutting performance of the chain. Be sure to observe the prescribed values.

A depth gauge is located on each cutting link in front of the tooth scapula. The difference in height between the top edge of the depth gauge and the front edge of the back of the tooth is defined as the distance of the depth gauge.

The depth of penetration of the upper blade into the wood (chip thickness) and thus productivity depends on the distance of the depth gauge. The distance of the depth gauge is set depending on the chain pitch and type of execution. Normally, it should be 0.5-0.8 mm, more often 0.6 mm. High values ​​will lead to an increased tendency of the chainsaw to kickback, too much grip and chain vibration. Low values ​​lead to a drop in performance. Since the distance of the depth gauge decreases with each sharpening of the saw due to a decrease in the upper edge of the tooth, the depth gauge also needs to be filed periodically. after 5-10 chain sharpenings.

Chainsaw chain sharpening machines

Stihl produces two modifications of hand-held machine tools. stationary FG 2 and mobile FG 1, mounted directly on the tire. There are analogues of lesser-known companies, comparable in price with the simpler devices described above.

The working part of these devices structurally resembles a bow saw, into which a round long file is inserted instead of a saw blade. FG 1 and FG 2 not only sharpen the chains, but also straighten them, adjusting the length of the top edge of all teeth to the same size. on the smallest tooth, which is taken as the control one. A rather complex configuration mechanism allows you to set all the necessary parameters. Sharpening is carried out in 2-3 movements, after which they proceed to the next tooth, keeping for it all the settings that were made for the control tooth. This ensures the same sharpening parameters for all teeth. When sewing the stopper, the round file changes to a flat file.

An electric chain sharpener for chainsaws is simple and convenient to use. It has an adjustment system that allows you to set the chain at the desired angle and bring the disc exactly to the sharpened edge. There are machines that automatically clamp the vice when lowering the disc onto the chain.

Sharpening kits

One of the most common methods is with a set of round and flat files, a holder, a stop template and a hook used to remove sawdust. For the correct positioning of the holder, special markings are applied to it, allowing you to determine the correct angle for sharpening. It is installed on the upper part of the tooth and the stop, while the round file remains under it and is located just next to the blade. Thanks to the holder, the file is at the correct height, or more precisely, protrudes 1/5 above the blade. For sharpening the cutting tooth, only round files are used, since the contour of the tooth has a rounded shape.

Kits must be purchased based on the chain pitch. You cannot use the same sharpening kit for different chains.

Before you start sharpening the chainsaw chain at home, the tire must be secured in a vice or with a clamp, the main thing is that the saw does not move during processing. Having installed the holder according to the markings, begin smoothly and without too much pressure, move the file strictly away from you 2-3 times. Similar actions are repeated with all other teeth. The file must be turned over from time to time so that there is no one-sided wear. The force of pressure and the number of movements for all should be the same, this is necessary for uniform sharpening of all teeth. If they are different, then cracks may form in the chain, which will lead to its breakage.

To make it more convenient to work, the teeth are first sharpened on one side, and after them the saw is turned over and the teeth are aligned on the other.

Start sharpening from the smallest tooth so that the length of all the others is the same as it. After the work on processing the blades is finished, go to the limiters. A template from the kit is installed on top of the chain in such a position that the stopper is in the hole. The protruding part is grinded with a flat file.

The video shows an example of how to sharpen a chainsaw chain with a file:

There is another set, which, instead of a holder, has one template, both for sharpening the blade and for grinding the stop. Install it so that the chain falls into the holes. Then the round file is placed on top of the rollers and fed under the blade. During sharpening, make sure that it is always parallel to the side faces of the template.

There are 2 separate holes for the stopper, labeled Soft for soft wood and Hard for hard wood. The protruding part from the slot, grind with a flat file.

Sharpening is carried out only from oneself and with smooth movements, the number of the latter should be the same for all teeth.

How is saw chain sharpening? Tips from the pros.

When working with a blunt or improperly sharpened chain, there is pressure on the tire. uneven abrasion in the places of work, the inner groove breaks, the shank burns, which leads to wear of the drive and driven sprockets. That is why, in order to extend the life of the chain and the entire saw set as a whole, it is necessary to follow the sharpening recommendations, contact professional craftsmen and carefully monitor the condition of your working tool.

How to sharpen the chain?

We recommend sharpening chains in certified service centers, although many do not support this opinion. mainly due to perceived savings.

Sharpening by a professional on the machine is the key to the correct implementation of all procedures. which ultimately prolongs the life of the chain and already saves money.

But the reality is that you may need to tidy up the chain yourself. You also need to prepare for such cases in advance and stock up on the right tool:

  • Round file of the appropriate diameter. The most important player in the sharpening business. But it’s not worth working with just a file! Manually, you cannot reliably stabilize the chainsaw (electric), as a result, the sharpening angle of each tooth will have its own.

File size chart according to chain pitch

Chain pitch

File diameter

Picco. low profile carbide link chains found on some STIHL saws.

Some manufacturers produce ready-to-use chain kits.

The round file and the guide can be replaced with a special hand tool for sharpening chains at the same time. It is designed so that it is fixed on the tire at the desired angle.

How to sharpen a chainsaw chain: instructions for working with sharpening accessories

Description of the sharpening process

Let’s take a closer look at how to sharpen a chainsaw chain. The first thing to do is to prepare a place for installing the clamp, or if the process will take place without it, then it is convenient to use a regular log as a stop for fixing the tire in the horizontal plane. The chainsaw is installed on a flat surface, the log is placed under the tire, the brake is activated.

To avoid injury when sharpening your chainsaw, be sure to apply the chain brake.

The next stage is direct sharpening of the tooth. To do this, a round file is made movements from the inner side of the tooth to the outer.

It is very important at this point to maintain the correct sharpening angle. The standard angle is thirty degrees from the file perpendicular to the plane of the tire. How to position correctly shown in the photo below.

In the process of sharpening a chainsaw for a non-standard cut, for example, longitudinal. The sharpened angle is changed to a less acute one. As a rule, it is no more than 10 °. It is in such cases that a holder, hand-held machines or filing gauges are used to control the sharpening angle.

Some manufacturers of chains for chainsaws, to facilitate sharpening, as well as to indicate the maximum possible sharpening, a special mark is made on the upper surface of the tooth.

By keeping the file parallel to the mark, you can be sure that the correct angle is being observed.

The number of working movements with a file should be the same for each tooth. This will allow all teeth to be ground evenly.

In the process of straightening the chain, it is customary to sharpen the teeth first on one side, and then on the other, this is convenient since there is no need to constantly change your position in relation to the chainsaw.

After the working teeth have been sharpened, it is necessary to adjust the height of the limiting tooth with a flat file. For this, the filing gauge is placed on the chain in such a way that the limiting tooth coincides with its slot, after which the protruding part is grinded with a file. This procedure is performed on all limiting teeth.

How I Sharpen My Chainsaw Chains. Works for Me!

How and how to sharpen the chain teeth

The saw chain teeth are non-standard. They consist of a base, a blade and a depth gauge. The blade has a vertical blade and a horizontal blade that falls at an angle. It is thanks to these blades that the chainsaw cuts wood. They work on the principle of a plane, cutting off pieces, and the limiter adjusts their thickness (the difference in height between it and the horizontal blade will be the thickness of the chips). You can sharpen the chainsaw chain manually or using a machine.

How to sharpen a saw chain?

When we say “saw,” we mean a petrol or electric chain saw.

The problem of dull chain teeth on a chainsaw (or saw) will gradually develop. Those who have owned the tool not so long ago often find it difficult to determine the sharpening point.

Chainsaw teeth

Chainsaw teeth have a specific geometry. You need to understand and know what part of them should be sharpened. In general, the “logic” of cutting wood resembles a plane.

The cutting surface has two edges. One is lateral, the other is slightly beveled. The cutting depth limiter adjusts the thickness of the chips. Let’s take a closer look. The elements of the cutting-working link are arranged as follows:

  • Base with axle holes;
  • Tooth scapula;
  • Cutting depth limiter;
  • End face of the blade (placement. vertical);
  • Upper edge of the blade (placement. horizontal);

Sharpened edge Dull After touching the ground

After sharpening, the height of the stop and the angle of the sharpened working edges should not differ greatly from the parameters specified by the manufacturer. This is an important condition and you need an “eye and eye” behind it. Otherwise, the saw will not work as expected.

Do not over-grind or change the location of the links. The normal operation of the instrument depends on the identity of their location. Otherwise, increased stress on the chassis, tire and engine is likely. The cut can be crooked. There is also a small chance of breaking the circuit.

Hand-operated machines

The design of such a machine is similar to a bow saw. Only where the saw blade is located is the round file. With such a machine, you can sharpen and straighten the teeth, adjusting the proportionality of the upper edges to the smallest (control) size. The mechanism allows you to accurately set the parameters. After adjusting the “control” tooth, sharpening is carried out in two or three movements. And then the transition. to the next tooth.

When it is necessary to grind off the stopper, we change the round file to a flat file.

Advantages of the method: Allows you to sharpen teeth, including those that have lost their original shape, in a high-quality, convenient and without large physical costs.

Disadvantages: The price of the tool and the distance from the possible site of the saw operation.

“After finishing the“ sharpening procedures ”, blow the chain with compressed air (from a compressor or pump) and put it briefly in clean engine oil. Of course, almost no one does such events, but for the chain, they will only benefit. “

What to choose for sharpening is up to you. This is due to how often you use your chainsaw. From the accuracy of handling it. From the quality of the purchased chain. And, of course, from the opportunity to spend a certain amount. It is impossible to compare methods, because as the German proverb says. “apples should be compared with apples”.

How to understand that the chain is dull

  • Increased physical effort;
  • Sagging (stretching) of the chain;
  • Vibration and “braking” cutting passage;
  • Inaccurate sawing and change in the type of sawdust (they become uneven with sharp “needle” edges, small and dusty). This is already the answer to the test.

“In the opinion of the experts and in my opinion too: well-sharpened teeth are more important than engine power.”

Why dull? The reasons are generally known, but I will name the main ones:

  • Intense or voluminous work;
  • Accidental contact with stone, earth, hard knots, etc.;
  • Mishandling (broad term).

We work with a file

The best solution is simple gadgets for sharpening work. This set includes a round and flat file, special holders, a gauge template, a hook for removing chips, etc. Structurally, “adaptations” may differ, but the functionality has a common logic.

The diameter of a round file is directly related to the size of the chain:

  • – Chains with ø 1.3. require a file of ø 4 mm (used much more often);
  • – Chains with ø 1.6. require a file ø 5.2 mm;
  • – To sharpen the depth gauge, use a flat file.

Sharpening process

  • Having previously “turned on” the chain brake, firmly grip the tire of the chainsaw in a vice (a firmly clamped saw is the key to successful sharpening)
  • Set the template so that the arrow points towards the nose of the tire. Be sure to mark (with chalk) the tooth from which you started sharpening, otherwise you can go along the second circle;
  • Sharpen in the direction of the arrows. Remember, there is a special factory cut on each tooth in the chain. It indicates the maximum sharpening angle.
  • In addition to the cutting tooth, there are stops on each link. They are sharpened as needed. This is necessary when, as a result of sharpening, the height of the tooth is reduced, and problems arise in the operation of the chainsaw. As a rule, the limiter is sharpened after 2-3 sharpening of the teeth;

“If you don’t have the skills to sharpen, it’s better to start with inexpensive chains.”.

Recommendations:

  • The file should not go beyond the top of the cutting edge by more than 1/5 of the working part of the file. The pressure is carried out with the same effort;
  • The movement of the grinding tool is performed in one direction “away from you”, and the number of movements for each tooth should be equal;
  • To sharpen a vertical plane, the position of the file must be at right angles;
  • For sharpening a horizontal plane, file position, at an angle of 20-30 °
  • If there are teeth of different heights, the reference is the smallest.

Advantages: Ability to “charge the saw” in the field. At the same time it’s cheap.

Possible ways and methods of sharpening the chain

First about the horror stories

If you cut with a blunt chainsaw, you will get three negative factors:

  • Reduce the efficiency of your process. For example, instead of two cubes, cut one (at the same time);
  • Expose the mechanism to intense wear, with the risk of destroying the drive sprocket and tire;
  • Get increased fuel consumption;

There is also a fourth, perhaps not so significant factor. “torn” cut of the saw cut.

And of course, you will get tired more, you will (perhaps) be angry with yourself, like “why should I be a fool, do not sharpen in advance, now suffer.”

Here is a test question for you (photo on the right). Guess what kind of shavings “came out” from under the sharp and dull chain? (the answer will be below).

Sharpening angle grinder

Professionals consider this work to be primitive. There is a risk of tire damage, and not only.

Process (seemingly easy, but really difficult)

  • The chain also stays on the bus;
  • We attach a metal cutting disc with a thickness of 1.5-2 mm to an angle grinder. It is advisable to take not new, that is, with a worn edge;
  • We put an obstacle in front of the chain and the tire (the chip will come off);
  • We sharpen at the desired angle;
  • Upon completion of work, the chain must be properly tightened.

With a professional approach and a “full hand”, the number of sharpenings in this case can be more than 7.

“For a beginner, it is better not to“ experiment ”with a saw, a chain, etc. with your body parts! “

Advantages of the method: Fast, cheap and does not take up energy;

Disadvantages: Requires special skills, a steady hand and the ability to comply with safety techniques.