2. Sawing tools

Tools for sawing are saw blades with teeth on one or two edges which are clamped in a hand hacksaw frame.

Figure 2 Hand hacksaw and saw blades

Different types of saw blades are used depending on the hardness of the material to be cut and on the type of cross-section of the workpiece.

The blades differ with respect to the saw tooth angles and the number of teeth on a fixed length of 25 mm (tooth pitch - 1).

Figure 3 Saw blades with different tooth pitch

Figure 4 Angles at the saw tooth

Saw blades for different hardness of material:

Hardness of material	Formation of chips at the saw tooth	Clearance angle (a)	Lip angle (b)	Rake angle (g)
Hard	Shaving -small quantity of chips	40°	50°	0°
Normal	Cutting -small quantity of chips	20°	65°	5°
Soft	Cutting -big quantity of chips	30°	50°	10°

Saw blades for different workpiece cross-sections and hardness of material

Type of saw blade	Cross-section of workpiece	Hardness of material	Tooth pitch (number of teeth on 25 mm)
Coarse	- Solid Sections (rounds, squares, hexagons)	Soft steel, brass and bronze	14
Normal	- Normal sections (angles, sectional steel) - Thick metal sheets	Steel of normal hardness, harder light metals	22
Fine	- Light-steel sections - Thin metal sheets	Harder steel, cast iron	32

Free cutting action of saw blades

Saw blades must not jam when penetrating into the kerf, therefore the width of the kerf must be bigger than the thickness of the saw blade.

Free cutting of the saw blade is achieved by:

- raker-set teeth or
- wave-set teeth of the saw blade.

Figure 5 Raker-set teeth

Figure 6 Wave-set teeth

After long use of saw blades the teeth will become dull and the free cutting facilities will also wear out.

Therefore, it is often not sufficient to sharpen the saw blade but restoring the free cutting facilities will also be necessary.

What makes the difference between the different types of saw blades?

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Which type of saw blade is used for sawing of steel of normal hardness?

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Why is the free cutting action necessary for saw blades?

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