Wood Flashcards
Rough sawn
Wood comes direct from seasoning and has rough surfaces produced during initial conversion
Rough-sawn wood will have nominal sizes rather than accurately finished sizes
Cheapest stock form
Planed square edge (PSE)
Wood has only one edge that is planed accurately, the rest are rough sawn
Planing removed roughly 3mm from the original nominal size
Planed all round (PAR)
Wood has sides and edges that are all planed square, straight and level
Smooth finish and ready to use
PAR board is 3mm smaller in every dimension than original rough sawn nominal size
Most expensive stock form to buy
Natural wood - width and joining
Comes from trees and is only available at a limited width due to the diameter of the tree trunk
To produce wider products natural wood planks must be joined together
Planks should be joined with the end grain going in opposite directions to minimise distortion
Manufactured boards standard sizes and width
Man-made produced in large sheets, typically 1220mm X 2440mm
Wide surfaces can be produced from one sheet without the need for joining
Mouldings
Pre-made mouldings such as skirting boards or wooden trims are readily available in standard lengths up to approx. 4m
Wood properties
Wood fibres grow along the length of the tree - consist of hollow cells (tracheids) supported by lignin resin
Expands and contracts with changes in humidity
Strong in along the grain, weaker across the grain
Converted (sawn into useful pieces) and then seasoned
Seasoning
Used to remove excess moisture (80-90%)
Helps prevent defects:
Warping Twisting Cracks Cupping Bowing
Trees should be felled in winter when they have less sap hence contain the least moisture - reduces seasoning time
Seasoning gives:
Greater immunity to decay and rot
Increased strength and stability
Helps preservatives to penetrate
Makes wood less corrosive to metals
Air seasoning
Traditional and inexpensive
Wood is stacked in a shelter outside - protected from the rain
Air circulates between the planks to remove excess moisture
A slow process - takes up to one year
Wood is used for outdoor products
Kiln seasoning
Expensive - uses controlled temperature and humidity
Wood is stacked on trolleys
Initially steamy in kiln then becomes hotter and drier
Quick process - a few weeks
Wood used for indoor products
Toxicity
Depends on the wood species, different species carry different risks - e.g. Respiratory infection, carcinogenic
Both wood dust and sap can be a hazard
Control of substances hazardous to health (COSHH) regulations 2002 - hardwood and softwood dusts have workplace exposure limits (WEL’s) of 5mg per cubic metre
Employers should provide PPE, extraction and ventilation systems
Oak
Hardwood
Hard Tough Durable Good insect and fungal resistance Attractive grain Good weather resistance Tannic acid - corrodes steel screws and fixings
Used for:
Furniture Flooring Boat building Cladding Joinery
Ash
Hardwood
Tough
Attractive open grain pattern - more flexible
Used for:
Tool handles
Ladders
Sports goods
Laminating
Mahogany
Hardwood
Can contain interlocking grain - more difficult to work, but it is generally easy to work with
Stable and durable
Rich, dark red colour
Uses:
Indoor furniture
Shop fittings and cabinets
Veneers - for manufactured boards
Teak
Hardwood
Hard
Tough
Straight grain
Natural oils - resists moisture, acids and alkalis
Uses:
Outdoor furniture
Lab benches
Traditional boat decks
