City and Guild PowerPoint Saw Blades and Parts When Cutting

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Level 2 Diploma in Site Carpentry

PowerPoint presentation

Saw blades and parts: successful cutting of timber bases and products

Unit 211: Set up and operate a circular saw



Types of use for circular saw blades

For circular saws to work safely and effectively, the correct choice of saw blade and the material the teeth are made from must be made.

Saw blades fall into two main categories:

• ripping down the grain

• cutting across the grain.

Most saw blades are manufactured from flat alloy steel.

To avoid the saw binding in the cut causing friction and heat, clearance must be provided.

This clearance is known as ‘set’.

The total width of the saw cut is known as ‘kerf’.



Spring set applied to traditional plate saw blades

Traditional set-on plate alloy is applied by bending the top third of the tooth over in alternative directions.

This type of set is known as ‘spring set’.



Tungsten carbide-tipped blades

Tungsten carbide-tipped (TCT) saw blades have a piece of tungsten brazed on each tooth.

The shape of the tungsten gives the saw blade its clearance (set).

Most saw blades today use this type of cutting material on the tooth tips.



Cutting different types of material

• Tungsten carbide is a hard material.

• It is suitable for cutting hard abrasive material as well as man-made materials.

• The tungsten enables longer running life between sharpening.

• This type of blade is the most common used today.



Types of blades

Ripping down the grain requires a different tooth design compared to cutting across the grain.

The most important difference between the two is known as the angle of ‘hook’ or ‘rake’.

This angle is referred to as positive or negative angle of hook.



Positive angle of hook

Positive angle of hook teeth should only be used for ripping along the grain.

They have a tendency to drive and bite progressively into the timber and may cause them to snatch when crosscutting.



Rip saw tooth design (positive hook angle)



Tungsten carbide teeth



Negative angle of hook

A negative hook angle can tend to push the timber away from the saw blade.

It also makes a stronger tooth point which is capable of withstanding the rigours of cutting across the grain of the timber.



Negative angle of hook for crosscutting



Additional features

Chip limitation:

• This reduces the amount that each tooth can cut and reduces the risk of kickback (material being forced back towards the operator).



Saw blade size and design speeds

• Circular saws are designed to rotate saw blades at the most efficient cutting speed.

• This speed is measured at its rim and is called the peripheral speed.

• If a smaller blade is fitted, the peripheral speed will fall.



Minimum size of blades to be fitted

• It is important than any new blade fitted to the machine must never be smaller than 60% of the diameter of the biggest blade size the machine will accommodate.

• There must be a notice showing the smallest size diameter blade to be used on the machine.



Minimum size of blade

Notice on machine showing minimum size to be used

Smallest not less than 60% of the largest size



Any questions?

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City and Guild PowerPoint Saw Blades and Parts When Cutting