How to correctly and at what angle to sharpen a circular saw blade
The use of circular saws is particularly common in the construction industry. Most jobs require making cuts and changing shapes and sizes of finished materials. Circular saw helps to cope with such tasks quickly and get a quality result. But the tool is not capable of serving forever, sooner or later it may become blunt. It is for this and need to know exactly how you can sharpen the teeth for a saw in domestic conditions.
Checking a circular saw for wear is an important issue that should be given special attention. Deep damage makes it impossible to sharpen the wheel. There are three basic signs that tell you that your circular saw needs sharpening or replacement:
- Severe heating of the guard and formation of smoke. A circular saw has a special guard that signals when the saw has blunted through heat. In particularly severe situations, smoke may come out of it.
- Sometimes the device of the saw implies a mechanical feed (if it is necessary to adjust the force of the pressure by oneself). In this situation, wear can be noticed if the pressure has to be increased.
- If when sawing wood there is soot and a strong unpleasant odor on the workpiece.
All of the situations described above tell the user that it is time to sharpen the device.
Sharpening with a machine tool
If there is an opportunity to purchase a special machine, then the process under consideration can be carried out with the maximum efficiency indicator. Such a device is compact, it can be used at home.
Particular attention is paid to the choice of abrasive wheel. In this case, note the nuances below:
- A carbide wheel is difficult to sharpen.
- When choosing, you should pay attention to grinding wheels made of elbor, with diamond grit or with green silicon carbide.
Sharpening process using professional equipment is very simple. The disk is fastened with a special locking device. It is designed with the design features of the wheel in mind. Let’s pay special attention to the fact that with the use of special machines it is very easy to sharpen circular saws with maintaining the necessary indicators. In this case the error is minimal. This is due to the fact that the design has a special angle indicator gauge. In order not to make a mistake at the time of the work with what teeth have already been processed, you should use a marker to mark the starting point.
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Carbide-tipped circular saws can lose their initial performance over time. But that does not mean you have to buy a new cutting tool. In most cases sharpening can be done at home, using any suitable machine.
Sharpening circular saw blades when work cannot be carried out. This can be understood from the three signals:
- The safety guard is heating up. Smoke rises from underneath and leaves the cutting area.
- Additional forces are required when infeeding the workpiece during cutting.
- Wood comes into contact with the cutting metal and causes burning and smells.
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Carbide tooth geometry
A carbide tooth has four working planes. the front (A), the back (B), and two auxiliary side planes (C). Crossing each other, these planes form cutting edges. the main (1) and two auxiliary (2 and 3). The given definition of the tooth edges and facets is given in accordance with GOST 9769-79.
The following tooth shapes are distinguished.
Straight tooth. Generally used in saws for fast, longitudinal cutting, where quality is not of prime importance.
Tooth oblique (beveled) with left and right angle of inclination of the posterior plane. Teeth with different angle of inclination alternate with each other, which is why they are called alternately beveled. This is the most common tooth form. Depending on the size of the resharpening angles, saws with an alternate tooth are used for cutting in both longitudinal and transverse directions in all kinds of materials (wood, chipboard, plastics). Saw blades with a steep backplane angle are used as undercutting saws when cutting double-sided laminated boards. Their use avoids chipping of the coating on the edges of the kerf. Increasing the bevel angle lowers the cutting pressure and reduces the risk of splintering, but also reduces the strength and durability of the tooth.
Bevel Tooth with Beveled Back-Plane
Teeth can be inclined not only on the back plane but also on the front plane.
Beveled toothed tooth with beveled front surface
Trapezoid tooth. These teeth feature a relatively slow blunting rate of cutting edges compared to alternate beveled teeth. Usually used in conjunction with a straight tooth.
By alternating with the last tooth and rising slightly above it, trapezoid tooth performs roughing, and the straight tooth following it performs finishing sawing. Saws with alternating straight and trapezoidal teeth are used to cut double-sided laminated boards (chipboard, hardboard, fiberboard, etc.).) as well as for sawing plastics.
Conical tooth. Saws with a tapered tooth are auxiliary and are used to notch the bottom layer of the laminate, protecting it from splintering as the main saw passes through.
The vast majority of tooth flanks are flat, but there are also saws with a concave flank. They are used for clean crosscut sawing.
Tooth sharpening angles
There are four basic angles of sharpening of the circular saw which, along with the shape of the tooth, determine its characteristics. These are the front angle (γ), the back angle (α) and the bevel angles of the front and back planes (ε1 and ε2). The angle of sharpening (β) has an auxiliary value as it is given by the front and rear angles (β=90°-γ-α).
Angle values are determined by the intended use of the saw.е. the material to be cut and the direction in which it is to be cut. Saws for longitudinal sawing have a relatively large front angle (15°-25°). Crosscut saws usually have an angle γ of 5 to 10°. Universal saws designed for cross and longitudinal sawing have an average value of the front angle. usually 15°.
Sharpening angles are not only determined by cutting direction, but also by the hardness of the material to be sawn. The higher the hardness, the smaller the rake angle and back angle (less sharpening of the tooth).
The rake angle can be either positive or negative. Saws with this angle are used for cutting non-ferrous metals and plastics.
Saws should only be sharpened by hand when using special fixtures. There is a sharpening machine for this purpose, which helps to carry out the process on the machine, not manually. The result is then more accurate.
In addition, other handy devices are used for sharpening:
It is not possible to replace the above devices. If at least one of these is missing, it cannot be sharpened.
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Methods of machining circular blades
To form the cutting edge, any sharpening machine is suitable, where the design of the equipment does not matter much. Of course, the angles of sharpening of disk plates with hardfacing are more accurately obtained on specialized equipment. However, its price is very high, so a standard sharpening machine with a possibility to change the inclination of the corundum disc is used.
To sharpen a circular blade yourself, you must strictly follow a few basic conditions:
- Usually the top edge is deformed. Sometimes edges are rounded up to 0.3 mm. Therefore, sharpening starts at the top.
- The machining is carried out taking into account the front edge and its back part.
- The operation is repeated at least 25 times. The thickness of the removed metal should not be more than 0,05-0,15 mm.
- The quality of cut must be absolutely uniform across the entire workpiece.
- After sharpening, it can be finished by hand with fine grit sandpaper.
How to determine the grinding angle of a circular saw
It is optimal to have an initial template according to which the geometry of the cutting edge can be corrected. It is often made of thin-walled stainless steel, less often of thick cardboard.
Tungsten carbide teeth are made according to GOST 9769-79. But their geometry and geometrical dimensions are defined by the manufacturer according to the purpose of the saw. If there is no template. you need to determine the required angles of sharpening by yourself. For this purpose it is recommended to use a pendulum angle gauge.
The technology of template making by your own hands.
- Take a new flap disc, which is identical to the blunt disc.
- On the hard sheet of cardboard draw precise contours.
- Use a pendulum angle gauge to determine the initial geometry of the carbide tips.
- Record data on the template.
It can then be used for self-sharpening on the sharpening machine or provided as a template for companies providing similar services.
Additionally, it is recommended to compare the data with the reference. In saws for longitudinal form, the rake angle is generally 15°-25°. For transverse models, this ranges from 5° to 10°. Universal models have a 15° rake angle.
It is important to remember that the rake angle can be negative. Similar models are used for cutting plastic sheets and non-ferrous metals.
Cutting element geometry
The saw blade, the tooth, has a defined geometry with more than one cutting edge. There is always one main edge and additional edges formed by intersecting planes “A”, “B” and “C” in certain combinations. when working with different materials it makes sense to choose blades with the most suitable tooth shape.
Saw blade with this working area is designed for roughing out sawn timber. The cut is coarse, of low quality, with relatively fast operations.
This shape of the cutting edge lies at the front edge of the cutter to produce cuts with a straight and accurate line. The saw is ideal for cutting composite materials such as plywood, chipboard (single and double sided laminated). After sawing hardwood, it is chipped and there are hardly any chips.
There are discs with a beveled leading edge, there are discs with a beveled trailing edge, or a version with alternating teeth (alternately beveled blade). When working with a tool with a beveled surface of the back edge of the cutting element when sawing hard wood, a clear qualitative cut is observed, but the saw quickly dulls.
The main advantage of this saw is the slow wear of the blade that eliminates the need for frequent sharpening. Usually the entire blade trimmer blade consists of alternating cutting elements. straight and trapezoidal teeth working in tandem. Higher trapezoidal tooth performs a roughing cut, allowing the main straight edge to cut more easily. Can be used for cutting plastic, hard laminates.
Auxiliary tool type, intended for making cuts in materials with laminated surface before the main cut. To avoid chipping on the workpiece’s front part. Such a saw blade is not used as an independent working unit.
It is convenient to cut material with blades with concave tooth form in cross cutting direction relative to fiber arrangement.
- The movement of the workpiece on the work table when cutting occurs with great physical effort;
- Cracks and chips are observed along the cutting line;
- The motor will overheat during operation;
- There is a smell of burning in the air;
- The material burns, which manifests itself as dark spots along the cutting line.
If you notice any of these symptoms, you must immediately begin sharpening circular saws with your own hands. Before starting work, it is also possible to check the sharpness of the saw either by feeling or by seeing with a magnifying glass. The cutting corner radius should be at a value of 0.1-0.2 mm. All cutting edges wear down when cutting large workpieces.
Circular saw blades can only be sharpened with your own hands if you have special tools. There is also a machine that allows you to automate the process, to make it more efficient.
To carry out work on sharpening the disk with their own hands, you can use the following tools:
You can also use a circular saw blade sharpening machine that does not need the above tools.
When to sharpen circular saws?
A rather important issue can be called determining when to sharpen circular saws. Severe wear and tear can make it impossible to perform such work. There are three clear signals that determine the need to sharpen the circular saw blade:
- Smoke formation, heating of the blade guard. The attachment usually has a special protective cover that can get hot if the disk is blunt. It should also be noted that in special cases there is smoke due to severe heating of the cutting zone.
- Also with mechanical feeding, when the pressure is adjusted by your own hands, you should give a lot of force to get the desired result.
- When processing wood or other material, there are traces of carbon residue and a corresponding odor in the cutting zone.
In the above-mentioned situations it is recommended to sharpen the circular saw blade.