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basic technology (Secondary School)

What is wood conversion?

Wood conversion is the process where a newly felled tree is converted into workable lumber. There are many different cuts that can be used to convert a downed tree to lumber.

FULL ANSWER

If the lumber is going to be used for construction, the wood is cut plain or through and through. This is less expensive to cut, and while it does produce increased chances of cupping, the wood is stronger when used properly. If the lumber is intended for decorative purposes, it is cut quartered or rift sawn. This is more expensive and produces more waste; however, the wood is much more decorative in appearance and is less prone to both cupping and expansion.

Conversion and processing

Conversion

The conversion of timber is a phrase usually used in reference to turning a log into a pile of boards/planks. This is done using a saw mill of some kind. There are several things that need to be taken into account when sawing up a log. It is important to take into account the taper (the difference in size between the two ends of the log). The size of the taper affects how a log needs to be cut up in order for the best use to be made of its timber. The size of the planks or boards that are needed, any heart rot or shakes (cracks) in the log and how round the log is, are also factors that affect how it should be sawn up to get the best use out of it.

When converting timber using a saw mill, having a handy local saw mill can be very useful. However, depending on the quantity of timber that needs to be sawn up, and the distance to the saw mill, it may be better both environmentally and financially to hire, or even buy, a mobile sawmill.

 

Processing

Before wood can be converted or seasoned, it must be processed. After felling the tree, the branches need to be removed from the main stem leaving a clean trunk. This is then cross cut to the appropriate lengths required depending on whether it is providing wood for planking, stakes for fencing, firewood etc. The branch wood can also be useful for many purposes such as charcoal, rustic furniture and hedge stakes, so may need to be sorted.

 

Seasoning

Once wood has been processed and/or converted, seasoning must take place. Seasoning is the term used to describe drying wood. Seasoning wood is important because otherwise it will shrink during usage and be more susceptible to rot. In the case of firewood, the less moisture it contains, the better it will burn and the less smoke it will produce.

When seasoning wood, in whatever form, air circulation is vital. If air circulation is insufficient, moisture will be trapped between the wood stopping it from drying properly and causing bacterial or fungal decay. Unless it is dried using a kiln, wood takes around two years to dry out properly.

 

Firewood is simpler to season than sawn wood as there is no need to worry about the wood splitting or becoming stained. So long as it is stacked under shelter with sufficient gaps for air flow it will dry out well. Two methods of seasoning firewood are as follows. Cut logs to size (4ft lengths are traditional), cleave the logs in to quarters or smaller depending on their diameter and stack the lengths for a year. Then saw them into useable lengths and stack them for a further year until they are ready to use.

Alternatively leave them to dry in the round for a year then saw them into stumps and split them using an axe or maul. However you chose to split them, when stacking firewood the layers should be stacked alternately i.e. if the first layer is stacked facing forward the second should be stacked facing sideways.

 

Stacking sawn planks or boards is different however. They do not want to be touching or they will not dry properly and will probably end up stained. To allow air circulation, small bits of wood often called sticks or stickers are place between the planks as they are stacked. There is no set size for these sticks though they are usually around 1×1 inch. The smallness of the sticks minimises contact and reduces the likelihood of stain however to further reduce the risk it is important that the sticks are free from dirt or decay.

 

Another issue with seasoning sawn planks or boards is their tendency to warp or develop shakes (splits). To avoid this it is important that the sticks are placed evenly throughout the stack, both horizontally and vertically otherwise the pressures placed on the timber will be unbalanced and this causes warping. Also the planks or boards should be stacked out of direct sunlight as its heat accelerates the drying process. If the timber is dried too fast, then the inside will not be able to dry as fast as the outside and so the outside shrinks faster which is what causes shakes.

 

Question:

  1. what is wood conversion
  2. define wood seasoning

 

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