An example of a warped plank compared to a well chosen unwarped plank

The Chippendale International School of Furniture, half an hour from Edinburgh, is situated in rolling East Lothian countryside close to fantastic mature forests of oak, elm, lime, ash, chestnut, sycamore and beech trees; an environment with all the raw materials needed to make flawless furniture.
“We teach students on our nine month course to plant a tree, choose a tree, fell it and plank it,” says Anselm Fraser, Chippendale Furniture School Principal.
“There is much more to selecting a good tree for furniture making than you might think. You need to understand the effects of shrinkage, defects in the wood and warp.”
Here are some of the useful tips that students at the furniture design school are given on how to choose wood for the furniture pieces that they make each term (you can see more photos on Flickr and slides on these tips) :
•    A hardwood tree should generally be about 150 to 200 years old. An oak tree, for example, should be about 200 years old. Trees that are too old usually suffer from rot and other defects, which means they often cannot be used for furniture making.
•    The wood in a felled tree dries out and shrinks as it ages. After 6 months you may see radial checks and splits towards the centre of the wood and tangential (clockwise or counter clockwise).
•    Boards cut from a fresh cut log will not show any shrinkage. However, after six months boards cut away from the heart of the log may show some warp due to tangential shrinkage. Shrinkage takes place around the growth rings. So, boards need to be cut from the centre of the log to reduce the chances of warp.
•    When shaped pieces of wood are cut too early from a log they will also end up distorting as the log seasons. Cut wood circles will end up more like ellipses, and square cut pieces can turn into parallelograms.
•    Stresses in a tree can appear in planks cut from it a year later! If a tree is in a windy location, the wood can become ‘cork screwed’. The wind can result in planks being springy, bowed, cupped or twisted. So, you should not buy a tree in an exposed windy location on the top of a hill or standing alone in the middle of a field.
•    Watch out for natural defects in a tree such as a cross grain, a diagonal grain or a spiral grain (also called ‘corkscrewed’), as well as the effects of knots.
•    These defects can also make it difficult to plane or work with pieces of timber: the fibres of growth rings may run in different directions, grains may be interlocked or wavy.
•    You also need to ensure that the tree is felled in the right way. Bad felling techniques can result in ‘shakes’ creating cracks in the heart of the log like a ring, a cup or a star.

“At Chippendale Furniture we have stocks of locally cut boards that we ‘air season’ outside in the yard. A 1” thick board needs to be air seasoned for 1 year; a 2” thick board for 2 years…. That is why buying 1” thick seasoned boards is significantly less expensive than 2” boards or 4” boards.

“Our students also learn to work with wood with attractive defects; these pieces can be used to make artistic furniture pieces like table tops and facings on drawers,” adds Anselm Fraser.
For details of Chippendale International School of Furniture’s intensive 9 month furniture design course, please visit www.chippendale.co.uk or www.chippendaleschool.com