timber characteristics

Level 1 Diploma in Carpentry and Joinery

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Unit 115: Produce woodworking joints

Timber Characteristics

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Objectives

To be able to

1.4 State the characteristics of different woodworking materials


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Solid Timber Classification

Hardwood comes from deciduous (broadleaf) trees. Broadleaf trees drop all their leaves by the end of Autumn. This prevents loss of water from the tree in Winter (which would otherwise kill it).

Softwood comes from coniferous (evergreen) trees. Evergreens have small, needle-like leaves which minimise loss of water from the tree. It keeps these leaves all year round.


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Solid Timber Characteristics

Hardwood isn’t always hard timber: balsa is a “hardwood”; it is used for model planes; it is one of the softest and least dense timbers available (balsa is Spanish for raft, so-called because balsa wood floats).

Softwood isn’t always soft timber: yew is a “softwood”: some yew trees in the UK are over 1,000 years old; they often grow only 10 centimetres in 20 years. Yew timber can be very close-grained, dense and hard.


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Early Wood and Late WoodEarly wood• Trees grow quickly in spring and

summer, when temperatures are warm and there is plenty of water and rotting nutrients. Early wood rings are lighter, wider and a little softer.

Late wood• Cold weather and short days in Autumn

into Winter will first slow down and then stop tree growth (both deciduous and evergreen species). Late wood rings are darker, less wide and harder.


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Solid Timber SIZES

Softwood that is sold for construction is sold either rough sawn or Planed All Round (PAR). The edges of PAR may also be eased (rounded), for handling.

Hardwood is sold by the board foot (or part thereof).

“Board foot” is a one-foot length of a board that is one foot wide and one inch thick.

Hardwood is sold rough sawn and usually with the waney edge intact.

PAR softwood is sold in nominal sizes (eg 4 x 2 inches); however, in the price you will have paid for the planing and so will only receive reduced size timber: eg 4”x2” becomes just 94 x 44mm for the buyer.Softwood is sold in both off-the-shelf finished sizes (eg for door linings) and in linear lengths, from 2.1m, increasing by 300mm up to around 5.1m


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Wood-based materialsWood-based (sheet) materials are made from timber. Resin glues are used to bond together the wood fibres, chips, flakes or veneers into sheets.


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Medium Density Fibreboard

Positive characteristics Negative characteristics• Smooth surface finish • Heavy

• Very stable (so long as it is kept from exposure to moisture)

• Swells up and ‘blows’ when exposed to moisture

• Relatively cheap • Holds nail and screw fixings poorly

• Takes paint finish without need for primer or undercoat

• Cannot be joined using many standard joints (eg dovetails)

• Works, shapes and machines easily but…

• Fine dust produced during cutting is extremely hazardous to health leading to lung disease

MDF is made by breaking down hardwood or softwood waste into fine fibres which are then re-formed into panels using resin (glue), heat and pressure.


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MDF Variations

• Moisture resistant

• Fire retardant


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Hardboard HDF• High density fibreboard (HFC)

is more commonly known as hardboard. It is manufactured from fine wood fibres, making it cost effective.

• Commonly used for floor covering and levelling of old floor boards.

• One face is smooth while the other is textured to give grip on the surface.

• Available usually in only 3mm thickness.


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Chipboard• Chipboard is manufactured

from wood chips and sawmill shavings bound with resin, then pressed and extruded.

• It is the lightest and weakest type of fibreboard.

• Melamine-faced chipboard (MFC) improves the look and resilience of standard chipboard.

MFC


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OSB (Sterling Board)• Oriented Strand Board OSB

is manufactured in a similar manner to chipboard but uses machined wood flakes (strands) compressed in specific orientations (directions). This gives improved strength to the finished board.

• Most common uses are as sheathing in walls, flooring, and roof decking. Suitable for exterior wall applications.


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Plywood• Thin veneers (plies) of solid

timber are glued together with the grain direction of each layer turned by 90°to the next.

• This makes plywood the strongest of all wood-based sheet materials, and considerably stronger and more stable than most solid timbers.

• There are always an odd number of plies (3, 5, 7 etc) so that the grain on both outer faces always finishes in the same direction.


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Blockboard• A core of softwood strips, faced

both sides with a sheet of plywood.

• The difference between the three types of blockboard is only in the width of the timber strips used in the core (lamin is highest grade).

• Good resistance to warping but not for external use.

• Used in furniture manufacture including fitted kitchens, bedrooms and better quality shop fitting.

• Wide range and quality of face finishes.


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Wood-based materials SIZESWood-based materials are supplied as 8 x 4 foot sheets (2440 x 1220mm).

The sheets are available in standard thicknesses: usually from 6mm to 9mm to 12mm and upwards (in 3mm increments).


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Why do we use wood-based materials?

StabilityTimber boards crack, shrink, twist and warp. Sheet materials are more stable (if stored and used correctly).

ConsistencySheet materials are produced in standard sheet sizes and thicknesses which will be UNIFORM dimensions every time.

AvailabilitySheet materials can be purchased anywhere.

StrengthSome sheet materials are VERY strong.

EconomySheet materials are cheaper than solid timber and produce less waste when cutting to size.

timber characteristics

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