circular saw

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Construction table saw
Circular saw powered by a tractor

A circular saw is a power tool for cutting separation of workpieces. It is used for sawing of wood , metal , plastic and other materials .

drive

In stationary machines, the circular saw shaft is often driven by V-belts, toothed or flat belts via pulleys. Different speeds can be achieved with pole-changing three - phase motors . Many electrically operated circular saws are now directly driven.

The cutting speed results from the speed and diameter of the saw blade. The ideal cutting speed depends on the material to be cut. Many machine manufacturers also offer frequency-controlled three-phase motors, the speed of which can be continuously adjusted (often in the range from 1500 to 6000 min −1 ).

Carbide- tipped circular saw blade

Circular saw blades

In addition to the traditional circular saw blades made from one piece of sheet metal, composite circular saw blades with cutting edges made of hard materials are predominantly used today .

One-piece circular saw blades
are punched out of a piece of steel strip , set and sharpened by filing or grinding .
Composite circular saw blades
consist of a metal support body onto which cutting edges made of hard metal or polycrystalline diamond are soldered. Since the cutting edges are wider than the metal support body, a is cabinets of the teeth not necessary. In order to avoid twisting the blade due to thermal expansion , fine cuts or recesses are often provided between the teeth, which act as expansion joints .

The area of ​​application of the saw blade depends on the cutting geometry of the saw tooth. This includes, for example, the tooth shape or the number of teeth (tooth pitch).

The selection of a saw blade depends on the material to be cut, the cutting direction along or across the grain, the wood moisture, speed of the saw shaft (cutting speed), feed speed, motor power as well as the desired cutting quality and service life of the blade.

Tooth shapes

Flat tooth
For rough cuts in the grain direction
Alternate tooth
Also known as the universal blade, as it is suitable for rip and cross cuts.
Hollow tooth
For veneered surfaces, as the cavity guarantees tear-free work. Pay attention to the cutting speed.
Trapezoid tooth
Ensures good results on painted and coated surfaces.
Trapezoidal flat tooth combination
Suitable for plastic up to 10 mm as well as panel materials, since chip evacuation and tear-free cutting are possible.
Roof tooth flat tooth combination
For plastic-coated flat press chipboard

Fine-toothed saw blades with around 48 teeth and a blade diameter of 150–200 mm are used for panel and composite materials, for plastics and aluminum as well as for cross-sections in solid wood. Longitudinal cuts in solid wood, on the other hand, are carried out more quickly with coarser teeth, for example with 24 teeth with a blade diameter of 150–200 mm.

The size and design of the circular saw blades are typified in the trade by means of 5 items, this is usually printed on the saw blade. Example: 216 × 2.4 × 30/40 / max. 7000. The first number describes the outer diameter of the saw blade in mm, the second number the cutting width in mm, the third number the hole circle diameter in the center of the saw blade, the fourth number the number of teeth and the fifth number the max. Speed ​​at which the saw blade may be operated.

Stationary circular saws

Stationary table saw, here as a format saw

The work table is attached to the machine stand of the table saw. This has a passage opening for the circular saw blade. Inside, the machine units for driving the saw shaft as well as the mechanics for the vertical and inclined position of the circular saw blade are housed. Pivoting and height adjustment are carried out using a handwheel or an electric motor. The inclination allows the precise sawing of angles between 0 ° and 45 ° (often from −1.5 ° to + 46.5 °). Some machine manufacturers have also been offering sliding table saws with a swivel range of 92 ° (2 × 46 °) since 2006 . Depending on the manufacturer and the swivel mechanism used, the max. The saw blade protrusion when swiveling from + 46 ° to −46 ° can vary. The rip fence is on one side of the machine table. It enables workpiece to be cut across the width, with the required dimension being preset on a scale. With sliding table saws, a roller table is attached to the opposite side of the machine. This takes up the angle-adjustable cross stop. Workpieces are placed on the roller table and guided past the circular saw blade. Here, too, the desired dimensions and angles can be preset on the corresponding scales. The cross stop can be removed for reasons of space.

With pull saws there is the additional possibility of fixing the workpiece and moving the saw blade. This is particularly useful for making oblique cuts or for cutting particularly long workpieces across.

Variants of stationary circular saws:

Inner hole cutting

The inner hole separating enables highly precise cuts with very thin blades or foils. The cutting edge is on the inside of a round recess in the center of the circular saw blade. The saw blade is clamped on its outer edge and hardly vibrates when sawing. With a minimum cutting width of 0.3 mm, a. Semiconductor blanks cut into wafers .

Circular saws

While with stationary circular saws the workpiece is guided over the work table, with a hand-held circular saw the tool is guided over the workpiece. Compared to the work table of a stationary circular saw, the base plate of the hand-held circular saw is relatively small. The top of the saw blade is covered to prevent injuries and chips from flying around. The lower part of the saw blade is covered with a movable guard (except for the plunge-cut saw ), which is only pushed back when it penetrates the workpiece.

In a plunge-cut circular saw, the drive and the saw blade are movably mounted on the base plate, so that the saw blade does not protrude downward from the base plate in the rest position. To cut, the saw blade is moved down through the base plate. This is also possible during operation, so that openings can be cut out of plate-shaped workpieces as well as grooves and slots, which is often necessary in furniture construction in particular.

  • Circular saw

  • Plunge circular saw

  • Saw blade and riving knife above

  • Saw blade and riving knife swiveled downwards

Today, the saw blade is usually placed directly on the drive shaft to save space. The machine is activated on the handle by a switch with a lock button. The switch is only released by pressing the lock button in order to prevent the machine from accidentally starting. The chips are usually blown to the side or sucked off through transport channels. Operating a circular saw is usually uncomfortable for left-handers .

In order to make longer straight cuts, circular saws are guided along a stop. Hand-held circular saws are often used with guide rails offered by the manufacturer , the webs of which fit into corresponding grooves on the underside of the saw. The rail can be placed on the workpiece in a non-slip manner and makes it easier to guide the machine precisely.

In order to reduce the tearing of fibers on the underside of the workpiece, the saw blade should be set to a cutting depth that corresponds to the workpiece thickness plus about 2 mm.

To reduce tearing on the top of the workpiece,

  • another (worthless) workpiece is placed on the surface and both are severed together,
  • a guide rail with elastic splinter protection is used or
  • Before the actual cut, the cutting line is pre-scored by setting the saw blade to a cutting depth of just 2 millimeters and slowly moving the saw against the usual cutting direction. The saw blade and workpiece move exceptionally in the same direction.

Work technique

Angle cuts and accuracy

The angular accuracy of a transverse stop for 90 ° cut-to-length cuts, which is particularly necessary for furniture construction, can be checked with the "5-cut method": a remnant or board is trimmed five times (or more) at right angles, the board after each cut is rotated by 90 ° so that the last cutting edge rests on the guide rail. The first cutting angle is marked on the plate. After the last cut, the edges of the sample should ideally be exactly parallel or the opposite sides of the same length. The angular deviation of the saw blade corresponds to the measured now five-fold angular deviation divided by the number of cuts.

The angular accuracy of a 45 ° cut can be checked by cutting a board to length at a 45 ° angle. Turned and put together at the cutting edges, a 90 ° angle should be achievable, here the angular deviation of the saw blade is half the measured deviation of 90 °.

Stationary saws for the home improvement market should have adjustable but firmly lockable cross stops. Angle adjustments "from + 45 ° to -45 ° or snap-in at 90 ° with adjustable miter saws are of no use if all the angles advertised cannot be reached because of the inaccuracy ( insufficient precision ) of the cross-stops. In addition, all snap-ins should have no wobbling effects "precisely hold the preset angle.

Accident hazards

Circular saws are among the most dangerous machines in woodworking. They are often underestimated, even by experienced users. For accident pensions, circular saws are the most common accident triggers.

In addition to workpieces being thrown away or a hand slipping, the causes of accidents include , for example, safety deficiencies in the machines, lack of instruction , lack of knowledge of auxiliary equipment for safe handling of workpieces, incorrect and risky habits including unsafe working methods or sawing unsuitable materials (such as polystyrene foam which melts and sticks to the saw blade).

The workpiece can be carried along by the rear upward rotating saw teeth or the saw blade surface and thrown against the operator . There is no resistance that the workpiece exerts when it is pushed forward, which means that the pushing hand can get into the saw blade.

Very old circular saw models were often driven by means of drive belts as a connection to the motor. Often these straps are uncovered, so that the user's clothing can become entangled in the strap or injury if the strap slips off.

Protective measures

Security advice:

Definitive stamp from the Accident Prevention stamp series from 1972

Tools that run fast involve risks and should therefore only be used by knowledgeable people. Compliance with all safety regulations and the use of the given safety devices (e.g. blade cover, riving knife, push stick, feeding aids) are essential. Circular saws cause an A-weighted sound power level of up to 110 dB. Working with hearing protection (ear muffs or foam plugs) and other safety techniques is therefore absolutely necessary. The upper limit of the "daily noise exposure level" for an entire working day is often reached after only two minutes during circular sawing work.

Gloves must not be worn when handling moving machines, as they can get into the machines and pull your hand into them.

Old circular saw from 1950 without guards
Tilting saw

In agriculture with a traditional economy without a throw-away mentality , inherited outdated devices are often in use that are not equipped with effective protective devices (riving knife, cover, etc.) and therefore cause high accident rates. Switching to modern devices can significantly increase security. To cut waste wood and firewood to length, tilting saws are better suited than circular table saws; the risk of injury is considerably lower.

Technical protective measures

Riving knife

The most important and most effective safety device on the circular saw is the riving knife . It is located behind the saw blade in the escape of the saw. There he keeps the kerf open. Wood that is cut in the direction of the grain can bend due to wood tension and jam the saw blade in the process. Unless the saw blade is blocked, they are usually picked up by the ascending saw blade and thrown upwards or against the operator. A correctly installed protective wedge keeps the cut workpiece apart and prevents it from getting jammed, with hand-held circular saws it prevents kickback and damage to the cutting edge due to improper guidance.

When the kerfs behind the circular saw blade are kept open, the riving knife is intended to prevent the tensioned wood from contracting again behind the saw blade after the cut. Therefore, it must have a certain width, which depends on the width of the kerf [Sfb] and the thickness of the blade [Sbb] of the saw blade. The formula “gap wedge thickness = (Sfb + Sbb) divided by two” provides a guideline value. In addition, the riving knife can prevent reaching into the rising saw blade. To do this, the right riving knife must be set correctly: It must be as close as possible to the saw blade; Depending on the material to be sawn and the type of saw, the distance to the teeth may be a maximum of eight or ten millimeters, with hand-held circular saws a maximum of 5 millimeters; its upper edge can be between the height of the tooth base and two millimeters below the cutting edge flight circle. This means that hidden saw cuts are also possible.

The thickness of the riving knife must be between the width of the kerf and the thickness of the saw blade body. For different saw blade thicknesses, correspondingly thick riving knives are required. Sawing without a riving knife is only permitted for special work such as insert saw cuts or if technical measures reliably prevent contact with the saw blade.

Active protective measures

The partly mandatory and partly optional protective measures for circular saws include saw blade covers, including movable ones that are opened when the workpiece is fed in and are intended to prevent injuries if the operator falls. Suction devices connected to it , partly as devices for connecting industrial vacuum cleaners to reduce dust exposure and the risk of slipping on the floor, as well as cleaner cutting plane and view. An overrun brake that is triggered by the safety bar and emergency stop switch , as well as capacitive or other sensors that are supposed to detect when a person is touching the saw blade. Release systems for cross-cut saws that allow lowering or switching on. Flaps for circular saws that cover the saw blade. Undervoltage releases prevent the switched-on electric motor from restarting after a power failure.

Passive protective measures

This includes a push stick that is used to push small workpieces or the end of a larger workpiece towards the saw blade; a stop rail against which a workpiece is pressed by the rotating saw or by the operator; Sliding carriages and roller tracks with which a workpiece can be moved with reduced static friction ; Sufficiently large contact surfaces on both sides of the table and clamping devices that secure the workpiece.

Manual protective measures

The position of the operator is to the side, not in front of the saw blade. The workpiece is pushed forward with the thumb largely angled.

Others

Gervinus is considered to be the inventor of the circular saw.

literature

  • Wolfgang Nutsch: Wood technology expertise . 19th edition, Verlag Europa-Lehrmittel, Haan-Gruiten 2003, ISBN 3-8085-4019-2

Web links

Commons : Circular Saws  - Collection of images, videos and audio files
Wiktionary: Circular saw  - explanations of meanings, word origins, synonyms, translations

Individual evidence

  1. ↑ a b Wolfram Herzog: First steps with plunge-cut saw and guide rail , In: HolzUndLeim.de, August 21, 2014
  2. ↑ a b Note on the EU-wide adaptation of the guidelines for the riving knife, In: HolzUndLeim.de; accessed in February 2020
  3. ↑ Heinz Rösch: The 5-cut method for checking the accuracy of a table saw longitudinal cut . (PDF; 461 kB) on Heinz Rösch's private website
  4. ↑ a b Accidents on circular saws ... a classic! , at Steine ​​und Erden.net
  5. ^ German statutory accident insurance. (PDF) accessed on February 2, 2016
  6. ↑ Table and panel sawing machines Handling and safe working (PDF; 679 kB) Holz-Berufsgenossenschaft
  7. ↑ a b c circular saw: to blame for every fifth machine accident at work , bauernzeitung.at
  8. ↑ DIN EN 62841-2-5: 2015-05 Electric motor-operated hand-held tools, transportable tools and lawn and gardening machines - Safety - Part 2-5: Particular requirements for hand-held circular saws (IEC 62841-2-5: 2014, modified); German version EN 62841-2-5: 20
  9. ↑ Brochure Safe working in carpentry . auva.at, p. 19
  10. ↑ Occupational health and safety, joiner's workshops , professional association for wood and metal dguv.de ( Memento of the original from January 27, 2016 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. (PDF) p. 28 @1@ 2Template: Webachiv / IABot / publications.dguv.de
  11. ↑ ÖNORM EN 1870-14 - Safety of woodworking machines - circular sawing machines
  12. ↑ Occupational safety, accidents with circular saws ... a classic! at steine ​​und erden.net
  13. ↑ steine-und-erden.net stones and erden.net
  14. ↑ Georg Lehnert: The influence of technology and natural sciences . In: Illustrated history of the arts and crafts . Martin Oldenbourg, Berlin 1907, p. 450 ( archive.org ): “In the course of the nineteenth century, the saws experienced significant improvements, with the introduction of the circular saw invented by Gervinus in 1780, which Brunel set up for cutting veneers in 1808 and used his steam sawmill in Woolwich, the first ever applied. The circular saw gradually became established in the joiner's shops, followed by the band saw in 1854. "