Timber Defects powerpoint

Level 1 Diploma in Carpentry and Joinery

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Unit 115: Produce woodworking joints

Timber defects



Aims and objectivesAim:

Introduce learners to timber defects.

Objectives:• List at least two defects found in timber.• State at least two seasoning defects.• List at least two natural defects.• State at least one term for knots found in timber.



Timber defectsDefects are faults that are found in timber. Some present a serious structural weakness in the timber, others do little more than spoil its appearance.

Defects can be divided into two groups:

1. Seasoning defects

2. Natural defects



Seasoning defectsSeasoning defects can be further divided into:• Bowing• Springing• Winding (or twist)• Cupping• Shaking• Collapse• Case hardening



Bowing

Bowing is usually caused by poor stacking during seasoning. It is a serious defect, causing good timber to be suitable only for use in short lengths.



Springing

Springing is a edge way curvature of a board. It is usually caused by the release of internal stresses during seasoning.



Winding or twist

Winding, is also known as twist, is very serious as it restricts the use of the timber to short lengths. It is caused by poor seasoning and poor stacking.



Cupping

Cupping is very common in flat sawn boards. It occurs through shrinkage of the timber when drying.



Shaking

Shaking is caused by the board being dried too rapidly. It is particularly common at the ends of boards, spreading along the grain.



Collapse

Collapse is a rare defect caused by too rapid drying in the early stages of seasoning. The moisture is drawn out too rapidly causing dehydrated cells to collapse.



Case hardening

Case hardening is caused by too rapid drying, resulting in the outside cells of the timber drying and hardening, sealing off the moisture in the central part of the board.



Natural defects

Natural defects can be further divided into:• Knots• Heart shakes• Cup shakes• Star shakes



Knots• Knots mainly occur in softwood and mark the origin of a

branch in the tree.• Knots are termed either ‘dead’ or ‘live’ depending on the

condition of the branch which caused it. • Dead knots are often loose. • Small live knots are no real problem. • Small dead knots and large knots, either dead or live,

are a serious structural weakness.



Knots



Heart shakes• Heart shakes are usually the result of disease or over-

maturity of the tree. • The shakes radiate from the centre of the log and are

caused by internal shrinkage.



Cup shakes

• Cup shakes, also known as ring shakes, are caused by a separation of the annual rings and are usually due to a lack of nutrient or twisting of the tree in high winds.

• In bad cases, economic conversion of the log is very difficult.



Star shakes• Star shakes are radial cracks which occur around the

outside of the log. They are caused by shrinkage at the outside of the log while the middle remains stable.

• This is usually because the log has been left too long before conversion.



Aims and objectivesAim:

Introduce learners to timber defects.

Objectives:• List at least two defects found in timber.• State at least two seasoning defects.• List at least two natural defects.

• State at least one term for knots found in timber.



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Timber Defects powerpoint