Wood cutting saws fall into three basic categories – hand saws, back saws and special saws. The latter type of saws generally always have replaceable blades and consequently need little or no maintenance, but hand saw and back saw categories can be further sub-divided.
The factors most often quoted when maintaining saws or buying replacement parts are saw length, and the size and shape of the teeth. Saw length is measured only along the blade. Tooth size is still commonly measured in the UK according to the number of points per inch (25. 4mm) or teeth per inch. This is generally abbreviated to ppi.
Hand saws measure up as follows: Rip saw: A coarse saw for cutting along the grain of timber. Length is generally 660mm with 5 ppi. Cross cut: The saw for rough cutting across grain and also for cutting joints in heavier joinery work such as roofing timbers. Length is 610mm or 660mm with 7 or 8 ppi.
Panel: A finer saw for accurate cutting across the grain, used also for converting man-made boards and cutting certain joints in lighter joinery work. Length is 510mm or 560mm with 10 ppi. Panel saws with 12 ppi are also available for very fine cutting work in the more expensive ranges.
Back saws are designed mainly for cutting across the grain but they can be used also for cutting along the grain over short measures in jointing work. Tenon saws for general carpentry work are available in lengths of 300mm to 410mm with 12-14 ppi. Tenon saws for cabinet and high class joinery work are more useful for the home handyman and come in lengths of 255mm to 300mm with 16-18 ppi. Dovetail saws, small tenon saws for fine work and dovetailing, are 200mm in length with 20-22 ppi.
Saw teeth
A saw must be able to cut through a piece of timber without sticking and for this reason the teeth are set – alternative teeth are bent outwards to make a cut, or kerf, which is slightly wider than the blade thickness. Higher efficiency is achieved when the blade is taper ground though this is found only on high quality saws. Here, the back edges or sides of the saw are ground down to make the major part of the blade thinner than the edge from which the teeth are cut.
Tooth shapes vary according to the type of saw and the use to which it is put. Saws for cutting across the timber grain have to act like two parallel knives, 1.5mm-2mm apart which can sever timber fibres. In this cutting action, the centre fibres crumble into sawdust which is carried away in the gullets between the teeth.
Rip saws, on the other hand, have teeth like a row of small chisels alternately offset. This configuration enables the saw to shave away a kerf, in much the same way as a plane removes timber. Again, the shavings are carried away in the gullets between the teeth.
