Lexicon DIY-Knowledge

Circular saw blades


Hojas de sierra circular

Lames de scie circulaire

Circular saw blades are accessories for circular saws. The properties of circular saw blades have an influence on work progress, the quality of the cut and the service life in the various materials to be cut. The following criteria determine the key properties of circular saw blades for hand-held circular saws. In addition, you can choose between different blades for special purposes.

Saw blade material
Most saw blades for portable circular saws are made from only two materials: chrome-vanadium (CV) steel or composite materials. The core and the teeth of composite blades are made from different materials. In this case the teeth are usually made of hard metal (HM).

CV steel
CV saw blades are made in one piece. The blade core and the teeth are made of the same material. The teeth are wrenched in alternate directions, then hardened and ground. CV steel is rather elastic and excellent material for very sharp teeth with a lot of bite. You should use CV blades if you want to obtain a good quality cut in soft wood. If CV blades are not regularly resharpened, the blade will become useless because the increased friction of the blunt teeth will cause their tips to ?burn out?. CV blades are rarely used on hard wood and composite materials because they tend to wear out quickly.

TC blades
So-called TC (tungsten-carbide) blades have small hard-soldered tungsten-carbide chips as teeth. Hard metal teeth are extremely heat-resistant and stay sharp much longer, i.e. they have a much longer service life and are especially recommended for hard wood and composite material which more than justifies the higher price when compared to CV blades. These properties have made TC blades replace CV blades almost completely off the market for hand-held circular saws.

Number of teeth
The number of teeth on a circular saw blade determines largely the quality of the cut and the required operator pressure. The number of teeth must be regarded in proportion to the diameter of the saw blade.

Low number of teeth
Large gaps seperate the teeth allowing long chips to be quickly removed from the cut wood. As a result saw blades with fewer teeth are less inclined to clog up. For this reason saw blades with few but rather large teeth are mainly used to make cuts parallel to the fibres (lengthwise cuts). The quality of the cut is fairly rough.

High number of teeth
A high number of teeth ensures a very good quality of cut, especially for cuts across the grain cross-cutting). However, when used to make lengthwise cuts these blades tend to clog up and they require a lot of operator pressure.

Very high number of teeth
Saw blades with very high number of teeth (fine cut blades) are intended mainly for special applications which require an excellent quality of cut, and for rather thin stock. These saw blades are not recommended for lengthwise cuts. Blades with a very high number of teeth can only be manufactured with CV technology.

The so-called relief is necessary to ensure that the saw blade doesn?t get stuck in the cut. The geometry of the teeth makes sure that the cut is marginally wider than the blade core width. As a result there is no friction between the blade core and the wood. For practical purposes, the offset is obtained by bending the teeth in opposite directions or an appropriate tooth width.

Crossing means that the teeth are set in opposite directions and then sharpened. The teeth are exposed to a lot of strain on their tips and outsides which is why CV blades tend to get blunt rather quickly and overheat.

Tooth width
On TC blades the tungsten-carbide chips are slightly wider than the blade core which ensures the required relief or offset. The service life of these teeth is much longer than with conventional crossed teeth.

Tooth shapes
The tooth shape determines the service life and above all the quality of the cut.

Side set teeth (CV)
High quality of the cut since CV teeth can be ground very sharp. They tend to wear out quickly due to the high strain on their tooth tips. Not suitable for hardwood and composite materials.

Flat teeth (TC)
Low-cost tooth shape with all-round properties. With low number of teeth good cutting quality in brittle materials like particle board. Otherwise rather low quality of the cut and rough operation.

Alternate teeth (TC)
Alternating teeth reduce the strain on individual teeth. The results are a longer service life and a smooth cut. The pronounced tips on the teeth produce a good quality cut. Blades with alternate teeth are used for all kinds of wood, however they are sensitive to nails and other foreign bodies.

Trapezoidal flat teeth (TC)
The teeth are arranged in alternating sequence of trapezoidal and flat profiles and ensure an excellent load distribution which suits the TC material. These teeth are very robust, durable and produce a good quality cut. Recommended for cuts in hard materials. Relatively insensitive to foreign bodies like nails. Cuts in non-ferrous metals are possible.

Tooth position
The tooth position has a strong influence on the bite of a circular saw blade. It has to suit the material to be processed and the type of cutting operation.

Positive tooth position
?Typical? tooth position for wood cutting blades. The tooth?rips?into the material and therefore the operator has to apply less feed pressure. However, the load on the tooth tips is very high. When it hits on a foreign body (e.g. nail) or metal the teeth tend to break off. The tooth shapes recommended for this pitch are crossed, flat or alternate teeth.

Neutral tooth position
Here the strain of penetrating into the material is distributed over the entire tooth front which means that the strain on indivdual tips is reduced. This tooth type does not support the forward feed, and higher operator pressure is necessary. This tooth type is robust and absorbs hits on foreign bodies. Suitable for metal cutting operations. Used in conjunction with trapezoidal flat teeth.

Negative tooth position
Tooth position for special stationary applications. The tooth is pushed off the material. Danger of kick-back during hand-held operations. The material has to be pushed against the limit stops during stationary operation (trimming).

DOC limitation
The term depth of cut refers to the maximum chip size which a single tooth cuts off on its way through the material.

In soft materials (wood) the chip or cutting depth can be several millimetres without putting too much strain on the teeth or the machine.

In hard materials (metal) it is often necessary to reduce the maximum cutting depth to a few tenths of a millimetre. If speed and tooth quantity remain unchanged, work progress is also reduced if you limit the cutting depth.