Saturday, March 22, 2014

Timber work 03- Materials and Fixings

Obviously timber is the main material used to form timber items and components. Timber is a natural material which has many advantages over other optional materials.
  1. Timber being a natural product is a renewable source. With properly managed forestry plans trees are effective in reducing carbon dioxide levels in the atmosphere thus reducing global warming.
  2. Manufacture of timber products requires much less energy than alternative materials.
  3.  Does not cause any disposal problems
  4. Has a high strength weight ratio
  5. Aesthetically pleasing
  6. Has low thermal conductivity
  7. Easily worked with ordinary hand tools
  8. Strong joints can be made with many methods.

Trees from which timber is obtained can be divided broadly into two groups – Endogenous trees which grow inwards in longitudinal fibers such as banana, bamboo and palm trees, and Exogenous trees on the other hand which grow outwards by addition of concentric rings. Timber for engineering purposes is obtained mostly from exogenous trees.
Timber can also be divided into two groups namely hard wood and soft wood depending on the hardness, density and strength. Hardwoods are heavy, strong and dark in colour. Soft woods on the other hand are light weight, with average strength and light in colour. Mature trees are felled to obtain timber and converted into commercial forms such as planks, beams, posts or columns, roof members etc. Converted timber usually contains about 50% of moisture by weight. This moisture should be removed prior to use. Removal of moisture in timber to stabilize with the humidity of the environment is called seasoning. Seasoned timber discourages moisture movement, keeps away fungus, insects, prevents warping and shrinkage, and gives long life to timber. Seasoned timber when used in timber items and components should be preserved against insects, fungus and moisture movement by the application of chemicals, paints or waxes.
In addition to natural timber manufactured timber also finds wide usage in woodwork. Manufactured timber is usually made from wood waste. This helps to minimize cutting trees for timber and manufactured timber is being advocated for many engineering uses as an option for solid timber. Some of the manufactured timbers are:

1.  Plywood – made by pasting thin wood veneers of cheap timber faced on both or one face with veneers of good quality timber.  
2. Particle Board( Made out of wood chips, saw dust etc.)
3. Chipboard( Made out of wood chips, saw dust etc.)
4.  Medium Density Fiberboard (MDF) ( Made out of wood chips, saw dust etc.)
5. High Density Fiberboard (HDF) ( Made out of wood chips, saw dust etc.)
6. Hard board ( Made out of wood chips, saw dust etc.)
7. Lamin board (Made by framing cheap timber battens and facing with veneers)
8. Batten board  (Made by framing cheap timber battens and facing with veneers)
9. Synthetic timber – made out of synthetic polymers.

Manufactured sheet timber is usually 2.4m x 1.2m in size.

Components used for assembly of timber components are termed fixings. The different types of fixings used to assemble timber are

Wire nails - A nail is a pin-shaped, sharp object of hard metal or alloy used as a fastener. Formerly made of wrought iron, today's nails are typically made of steel, often dipped or coated with zinc to prevent corrosion.  Ordinary nails for wood are usually of a soft, low-carbon or "mild" steel (about 0.1% carbon, the rest iron and perhaps a trace of silicon or manganese).

Concrete Nails
Used to fix timber components to masonry. These are harder, with 0.5-0.75% carbon.]

Wood screws –
  1.Wood screws are the most commonly-used mechanical woodworking fasteners. They are used primarily for connecting wood to wood, and are popular for the clamping force that they provide to strengthen a joint. They can also be used to attach hinges, hardware, locks and other non-wood objects.
2.The gauge of screws range from No. 6 to No.12, No. 6 being the smallest.

3.Screw lengths are from 12mm (1/2”) to 75mm (3”).

4.Screws have three types of heads:
5.  Counter sunk
6. Raised head and
7. Round head.

8. There are three types of head slots:
9. Flat or single cut
      10. Philips head and

Bolts & Nuts
Bolts and nuts are a very strong method of fixing wood to wood or metals and other materials to wood. Sizes are specified by bolt diameter and length. There are many types of threads ranging from coarse to fine (on the No. of threads per inch).  Both left handed and right handed threads are made, but the majority being right handed (tighten on turning to right hand side)

Wedges are tapered pieces of wood which can be used as fixings in the assembly of timber parts. A typical example is the wedges in the figure used to lock the mortise &Tenon.
Dowels are rounded or square tapered pieces of timber driven through component parts to join them together.

The types of adhesives (or glues) available are so vast that any material can be pasted to any surface.
Adhesives are divided into two types depending on the method of setting.
Thermoplastic adhesives set either by loss of solvent or by cooling. It will soften again by applying the solvent or by re-heating.
Thermosetting adhesives set and solidify through a chemical reaction and the action is irreversible.

Types of adhesives

Animal glue – Made from hoofs, bones and hides of animals. Avilable in cake form or as small beads. Suitable for internal use and has high gap filling properties.
Fish glue – Made of fish offal and skins. Good for small repair work. Not suitable for structural work.
Casein glue – made from skimmed milk. The powder is mixed with cold water into a creamy paste. Good for internal work only.
Synthetic resins – Synthetic adhesives are very strong, durable and can be used both externally and internally. Some of the common types are:-
  •             Phenol Formaldehyde
  •            Resorption Formaldehyde
  •            Urea Formaldehyde
  •            Melamine Formaldehyde
  •            Polyvinyl Acetate
  •            Polyurethane glue


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