Buying Timber

Timber can be purchased sawn, planed all round (PAR), or, planed both sides (PBS) but with the edges left sawn. Sawn wood is very rough and is mostly used for structural work. To make furniture or cupboards, you will need planed wood. Planing timber means that between 3mm to 5mm of wood is removed, so a 25mm piece of planed wood ends up as 22mm. A board measuring 152mm long will end up as 146mm long, as 3mm at each end will have been planed. The annoying thing about buying wood at timber yards or DIY stores, is that the sizes referred to are still sawn wood sizes - even after it has been planed to make it smooth. So a 50 x 100mm PAR wood is actually 47 x 95mm.

When you buy timber, it's a good idea to try and buy the standard sizes as these are cheaper. Allow a little extra on lengths, in particular for cutting, and to compensate for any 'dirty' or damaged edges. A good rule of thumb is to add an extra 13mm for every 610mm. Always reject material with large knots as this is the sign of weak wood. Where there's a knot, there's often a bend or twist in the wood. Timber with bits of bark at the edges - effectively reducing the width because you'll have to cut it away - is called 'waney-edged'. End splits or 'shakes' are another common fault and can sometimes extend right up the board. These are usually caused by too-rapid drying and again you'll lose length because the split wood has to be cut away. Other defects to look out for are 'cupped' boards, where there is a warped curve across the width, and sapwood on the edge of boards (which is a lighter colour than the rest of the board), which is attractive to woodworm.

BASIC LENGTHS OF SAWN SOFTWOODS:

1.80m 2.10m 2.40m 2.70m 3.0m 3.30m 3.60m 3.90m 4.20m 4.50m 4.80m 5.10m 5.40m 5.70m 6.0m 6.30m

For planed softwood timbers, deduct 3mm from sawn sizes. For example, 25 x 50mm PAR (planed all round) is 22 x 47mm in actual size - although you should allow for some slight variations.

HARDWOOD SIZES:

Lengths: as available, due to different sizes of trees. If not available in 100mm increments, it is normally charged to the next 100 mm.

Widths: 50 mm, rising in 10 mm increments. Also depends on species of tree.

Thickness: 19mm, 25mm, 32mm, 38mm, 50mm, 63mm, 75mm, and 100mm, rising thereafter in 25mm increments.

MAN-MADE BOARDS:

Plywood

Thickness: 3mm to 18mm
Standard sheet sizes: 2440 x 1220mm (8 x 4ft) 1220 x 1220mm (4 x 4ft) 1220 x 610mm (4 x 2ft)

Chipboard

Thickness: 9mm, 12mm, 15mm and 18mm Standard sheet sizes: 2440 x 1220mm (8 x 4ft)

Melamine and timber finished chipboard

Thickness: 15mm
Plank lengths: 1820mm (6ft), 2440mm (8ft) Widths: from 150mm (bin) to 600mm (2ft)

Hardboard

Standard sheet size: 2440 x 1200mm (8 x 4ft) Thickness of standard hardboard: 3.2mm