11 conversion of timber
- 2. Chapter 11 Conversion of Timber
- 4. Converting logs Horizontal bandsaw Reasons to convert timber Allows wood to dry faster Provides wood of usable size and shape Allows the quality of the timber to be seen
- 5. Through and through sawing Plain/slash sawing
- 6. Advantages – Low cost and fast – Maximum width of planks obtained from log. – Little wastage. – Reveals attractive grain pattern, especially in softwoods. Disadvantages – Not suitable for structural timber – Some boards are all sapwood – With this method cupping caused by tangential shrinkage is a problem (cupping is the warping of the plank away from the heart of the tree)
- 8. Advantages – An attractive grain pattern is produced – Boards are more stable and shrink less – Boards wear more evenly,important for flooring Disadvantage – Expensive, as the log has to be first quartered then turned for every cut. – Because the log is quartered then cut again narrower boards are produced
- 10. Advantages – Produce board with flame figure – Tangential boards are strong boards, used for beams and joists – Heartwood and sapwood are easily separated – These boards can take a nail without splitting because of the position of their annual rings Disadvantages – Prone to shrinkage (Cupping) – It is expensive as the log is turned 90º for each cut
- 11. Exam question 1 Shown in the diagram are two methods for timber conversion. (a) (b) (c) Name the two methods of conversion shown in the diagrams. State two advantages and two disadvantages of each method. The diagrams show the ends of two boards, M and N. Which of the boards is most likely to cup? Give a reason for your answer. Describe, using a neat freehand sketch, the direction of cupping. (JC, HL, 2005)
- 12. Sample answer to exam question 1 (a) The methods of conversion shown are: A Through and through sawing, also called slash or plain sawing. B Quarter sawing or radial sawing. (b) Through and through sawing Advantages • • • There is very little waste from this method It gives wide boards It is a cheap and easy method Disadvantages • • • The boards are prone to cupping The boards have no particular grain pattern There would be a lot of sapwood in many boards so more likely to rot due to fungi and insects
- 13. Sample answer to exam question 1 (b) Quarter sawing Advantages • The boards are stable • The boards are hard-wearing and used in flooring Disadvantages • More labour required, as the logs need to be turned • More expensive • More waste produced
- 14. Sample answer to exam question 1 (c) The board most likely to cup is board M. This is because when the wood begins to dry, the cells shrink. The shrinkage occurs along the rings, which tends to pull the board into a curved shape as a result. The other board, N, will have more even shrinkage because of the arrangement of the rings as shown.