Materials - Timbers

Josh Ricketts says:

Materials

Timbers - Are renewable, natural and sustainable.

Lumber - Wood that has just been felled, so hasn't had any treatment.
Timber - Wood that has been sawn and worked with.

The two types of timber are;

Softwoods - Have pines and are evergreen. They are green all year round and have a less complex cell structure, are fast growing and therefore more harvests.

Hardwoods - Have leaves and are coniferous. They shed their leaves in autumn and have a more complex cell structure, are slow growing and therefore expensive. They are larger which means when harvested more wood is available.


Structure of Timber

Wood is fibrous with fibres down the length of the tree, like lots of long tubes glued together to form a complex and strong structure, which is easy to 'peel' along the grain and hard to cut across the grain. The tree is made from 55% cellulose and 28% resin. Timber is therefore as natural reinforced polymer.

From Tree to Saw

Step 1 - Harvesting - Cutting down the tree. Either chainsaws or two-man saws.
Step 2 - Conversion - Cutting trunk and large branches into boards. This is either slab or quarter sawn.

Slab Sawing uses the whole tree so there is no waste product but is not as stable and also more likely for twists and knots to appear. Quarter Sawing is most common for expensive hardwood timbers. This means more waste but more stability, also less liable to warp and twist and also a more expensive grain structure.

Another type of sawing is Rift Sawing. Riftsawn lumber is much more stable than plain sawn lumber. As shown in the drawing, each board has the same relation to the log, and therefore each board will have the same grain pattern. Rift sawing however has a very poor yield and leaves the trianglular wedges shown in the drawing.

Step 3 - Seasoning - Is reducing moisture content through two techniques;

Natural Seasoning uses air; the wood slabs are kept in a containers with openings which allow the air to flow over and under the wood to take the wood's natural water out slowly. Kiln Seasoning uses heat to physically force the water out of the wood using a kiln. Both techniques have advantages and disadvantages such as time and warping issues and quality.

Step 4 - Board Preparation - Wood is sawed to size and planning takes place to make the wood smooth. Wood can be planed all round (PAR) or just planed on two sides.


Aspects for Choosing Woods

Physical strength is very important; timbers are stronger along the grain than across it.
Aesthetic properties are important too; colour of the wood and grain structure change aesthetic qualities dramatically. 
Moisture changes the warping of the wood.
Protection is essential to stop the wet getting in and also becoming too dry, also stops insect attack.
Operating Conditions are important to consider, such as outside or inside or central heating.
Costs such as expensive softwoods or rare timbers, or cheaper softwoods have to be considered for the product.
Sustainability is important, environmental issues are important for the new sustainable sources wanted from the public.
Sizes of boards are also important for the product you're making and cost issues which may come with this.

Josh out.