Selection

Pine can be purchased with either a sawn finish or a planed surface. Sawn softwood will be at the size stated. However, when the wood is planed, about ^sin (3mm) is taken off every surface, but the stated size is what it was before it was planed: this is called the 'nominal' size. So, for example, a piece of planed timber 6 x lin (152 x 25mm) will have an actual size of approximately 53/4 x 3/4in (146 x 18mm).

The sizes given in the cutting lists for the projects are the actual dimensions that the wood should be. However, for some man-made boards such as plywood or floorboards, some manufacturers only specify the dimensions in metric or imperial, not both. This leads to difficulties when compiling a cutting list as some sizes do not translate from one to the other exactly. For example, the nearest equivalent to 7/i6in thick plywood could be 10 or 11mm. When you purchase boards bear this in mind, and get the nearest size available, in the measuring system you prefer.

Although at DIY outlets the wood is very often shrink wrapped and standardized, it is still possible to sort through and select the planks to suit your purpose. In fact, it is probably easier to be selective in a DIY outlet than at a traditional timber merchant, some of whom may charge extra to let you sort through the stack. Be careful when selecting sawn wood,

FIG 2.2

Undesirable: a dead knot, partially removed from its hole.

because it is not as easy to see faults as when inspecting planed timber.

Because you will need to be selective and discard wood with ugly faults, make an allowance of about 10% extra for waste when sorting the timber for a project.

FAULTS IN TIMBER

The different faults to be aware of are knots, resin pockets, warping, bending and twisting.

Knots

Knots are part of the inherent appeal of pine furniture and give the timber its character. However, some knots are desirable and some are not. Avoid very large, dark-coloured knots and those with cracks in them, as well as dead knots which might be loose in the knot hole (see Fig 2.2). Small, light brown knots are the ones to have (see Fig 2.3).

When selecting planks for a table or cabinet top, try not to use a piece that has a knot on the edge, because it will be harder than the surrounding area and therefore more difficult to work.

FIG 2.3

Desirable: a light-coloured, uncracked knot.

FIG 2.4

A resin pocket.

If a moulding of some kind is to be worked into such an edge, it will be very difficult to get it smooth. Similarly, when choosing wood to make a thin rail for a chair or table, do not pick a piece with a large knot in the middle as this will not only be weak but will also distort the shape.

If you have chosen a piece of wood with a dead knot which falls out after work has commenced, it can easily be glued back in. If the knot is cracked and breaks apart, as an emergency repair, it can be replaced with a plug made from a piece of similar-coloured wood.

Resin pockets

Resin pockets are found in nearly all" types of pine and should be avoided wherever possible (see Fig 2.4). They consist of small hollows in the plank that contain an extremely sticky, semi-liquid resin, and are usually revealed when the wood is planed. If resin pockets appear in the middle of a piece of wood already being worked on and it is not possible to use another, the hollows can be cleaned out and filled, or cut out completely and another piece of wood shaped and inserted. However, neither solution is very satisfactory, and the best answer to the problem is to avoid resin pockets in the first place.

Warping, bending and twisting

These problems arise because a tree has a high moisture content when cut down and loses that moisture unevenly through the wood as it dries out. Wet wood shrinks as it dries, setting up stresses within the planks that in turn cause faults to appear. To alleviate this, the tree is cut into planks and dried either in the open air or in a kiln. The idea is to bring down the moisture content slowly to the same level as that of the place where the timber will eventually be used.

When planks are being dried, they are kept in stacks that hold them flat. When they are unstacked, brought into the DIY store and then sold, the moisture content of the wood may be slightly different to that of the surrounding air, causing the wood to either shrink or swell across the grain. This effect is not usually very marked until the wood is moved into a centrally heated house, when the width of a plank can change by as much as 10%: this figure will vary depending on the type of wood and its moisture content. It is therefore best to acclimatize the wood that is going to be used for indoor furniture by storing it inside the house for as long as possible before work is started.

A badly twisted piece of wood is very difficult to correct and should be avoided. A piece that is bent can sometimes be corrected by more extreme bending in the opposite direction, using weights or clamps for two or three days (see Fig 2.5). The best way of correcting a warped plank -where the wood bends away

FIG 2.5

Bent pieces of wood can sometimes be remedied.

from the heartwood on the end grain - is to plane it to a smaller size (see Fig 2.6).

End of plank.

End of plank.

Plane to the dotted lines to produce a smaller but useful piece.

FIG 2.6

Correcting a warped piece of wood.

GRADES OF PINE

Pine is graded by assessing the amount of clear timber that is present in the boards, and the type of tree from which it came. If the wood is relatively free from knots, cracks, resin pockets and other faults, it will be of a high grade - referred to as 'appearance grade'. If it is not free from blemishes and flaws, it will be sold as 'building grade'. These two broad categories are subdivided still further by some timber merchants, according to the amount of defect-free timber and the straightness of the grain, although there is no consistency in the terms used for this. Generally, 'appearance grade' and 'clear timber' are of good quality in terms of appearance, while 'stress grades' refer to a lack of defects resulting in the timber being structurally sound and good for load bearing.

Unless otherwise stated, the planed timber sold in DIY stores will not be of the very highest grade. The sawn timber will be of the same or a slightly lower grade than the planed timber. Carefully select the planks you buy, and if you require clean planks for certain parts of a project either cut them from clear areas, which will waste some wood, or go to a specialist dealer who sells better grades of timber.

PREPARED BOARDS

Many DIY outlets sell pre-jointed pine boards 3/4in (18mm) thick, in a variety of widths up to 24in (610mm). The boards are shrink wrapped and may warp slightly when opened and left in a warm room. To counter this, they should either be used immediately or stored flat with some weights on top.

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