Shakes (timber)
Shakes are cracks in timber. Arising in cut timber the generally cause a reduction in strength. When found in a log they can result in a significant amount of waste, when a log is converted to lumber. Apart from heart shakes, often found in trees felled past their best, shakes in a log have no effect on the strength of shake free lumber obtained therefrom.[1]
They are often seen in oak-framed buildings, which are constructed of green oak which cracks while drying. Due to the immense strength of the oak beams, they are not a cause for concern in a properly engineered building, and are considered part of the charm of the style.
Heart shake
Heart shake is a crack in the heartwood, near the centre of the tree. It is caused by poor seasoning, or by using trees felled past maturity.
Star shake
A crack or cracks propagating from near the edge of the log towards the centre, usually along the line of the medullary rays. The cause is often rapid or uneven seasoning, causing the outside of the log to shrink faster than the heart. Exposure to the elements can cause star shakes, as can frost during the growth of the tree.
Frost shake
Frost shake begins on the outside where moisture has penetrated, and then frozen.
Cup or ring shake
A cup or ring shake follows the line of annual rings. The separation of the rings is generally cause during the growth of the tree, either by a check in the growth, or by bending and twisting under high winds.
Thunder shake or upset
Thunder shake is across the grain, and hard to detect until the boards are being planed. It is caused by shock to the wood, such as thunder, or concussion during felling. This fault seriously weakens the timber.
See also
References
- ↑ Practical Home Woodworking. Odhams. 1952. pp. 62–3.