The document discusses different types of circular saw blades and their proper usage. It explains that saw blades are categorized by their intended use for either ripping or crosscutting lumber. Ripping blades have a positive hook angle that drives into the wood grain, while crosscutting blades have a negative hook angle to push wood away. The document also notes that tungsten carbide teeth are common today as they enable longer life and are suitable for hard and manufactured materials. Proper blade size must also be selected to maintain efficient cutting speeds.

1. © 2013 City and Guilds of London Institute. All rights reserved. 1 of 16
Level 2 Diploma in Bench Joinery
PowerPointpresentation
Saw blades and parts: successful cutting of timber
bases and products
Unit 211: Set up and operate a circular saw

2. © 2013 City and Guilds of London Institute. All rights reserved. 2 of 16
Level 2 Diploma in Bench Joinery
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’.

3. © 2013 City and Guilds of London Institute. All rights reserved. 3 of 16
Level 2 Diploma in Bench Joinery
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’.

4. © 2013 City and Guilds of London Institute. All rights reserved. 4 of 16
Level 2 Diploma in Bench Joinery
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.

5. © 2013 City and Guilds of London Institute. All rights reserved. 5 of 16
Level 2 Diploma in Bench Joinery
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.

6. © 2013 City and Guilds of London Institute. All rights reserved. 6 of 16
Level 2 Diploma in Bench Joinery
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.

7. © 2013 City and Guilds of London Institute. All rights reserved. 7 of 16
Level 2 Diploma in Bench Joinery
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.

8. © 2013 City and Guilds of London Institute. All rights reserved. 8 of 16
Level 2 Diploma in Bench Joinery
Rip saw tooth design (positive hook angle)

9. © 2013 City and Guilds of London Institute. All rights reserved. 9 of 16
Level 2 Diploma in Bench Joinery
Tungsten carbide teeth

10. © 2013 City and Guilds of London Institute. All rights reserved. 10 of 16
Level 2 Diploma in Bench Joinery
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.

11. © 2013 City and Guilds of London Institute. All rights reserved. 11 of 16
Level 2 Diploma in Bench Joinery
Negative angle of hook for crosscutting

12. © 2013 City and Guilds of London Institute. All rights reserved. 12 of 16
Level 2 Diploma in Bench Joinery
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).

13. © 2013 City and Guilds of London Institute. All rights reserved. 13 of 16
Level 2 Diploma in Bench Joinery
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.

14. © 2013 City and Guilds of London Institute. All rights reserved. 14 of 16
Level 2 Diploma in Bench Joinery
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.

15. © 2013 City and Guilds of London Institute. All rights reserved. 15 of 16
Level 2 Diploma in Bench Joinery
Minimum size of blade
Notice on machine showing minimum
size to be used
Smallest not less than 60% of the
largest size

16. © 2013 City and Guilds of London Institute. All rights reserved. 16 of 16
Level 2 Diploma in Bench Joinery
Any questions?