Saw chain
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Saw chain, whether for handheld chainsaws, mechanical timber harvesters or chain routers, has undergone dramatic development since its invention. Modern chains designed for high power, high speed sawing applications will vastly outperform older designs, while allowing a far greater degree of safety and reliability in use. Constant design review and stiff competition between manufacturers in a very demanding market has also resulted in the development of of a large number of unusual chains for very specialised uses.
Early saw chain designs
Very early chainsaws used tooth configurations very similar to conventional hand saws. These were very simple saw teeth following a wave pattern (left, centre, right, centre) with no depth gauges as such, relying purely on bar pressure to limit the cutting rate. They were inefficient and slow in use, and were soon superceded by chipper chain. they required great skill and a lot of time to sharpen in the field, leading to extended downtime between sessions.
Chipper chain
Chipper chain improved dramatically on the performance of scratcher chain. Chipper used a tooth that was curled over the top of the chain, with alternate teeth pointing left and right. Ahead of the tooth was a depth gauge, which allowed for good clearance around the tooth for chip clearing while limiting the depth of cut and preventing grabbing or overloading.
Modern chain designs
For general use in forestry, tree surgery and firewood cutting, two basic configurations exist. Full chisel chain has a square cornered tooth, splitting wood fibres easily in the cut for fast, efficient cutting in clean softwood. Semi-chisel chain has a rounded working corner. While slightly slower than full chisel, it retains an acceptable cutting sharpness for longer, making it the preferred choice for dirtier wood, hard or dry wood, frozen wood or stump work, all of which would rapidly degrade a full chisel chain.
Chain specifications and dimensioning
Cutting chain comes in a bewildering variety of configurations, but these come down to a few key dimensions for replacement or specification purposes.
gauge: the gauge of the chain is the thickness of the drive links, and is dictated by the gauge of the bar it must be run on. Usual gauges are .050" (1.3 mm) - .058" (1.5 mm) and .063" (1.6 mm). Chain and bar gauge must match; a chain that is too large will not fit, one that is too small will fall sideways and cut poorly.
Pitch: the pitch of the chain is the average distance between two rivets. As the distance between rivets varies, the pitch can be measured by measuring between three rivets and dividing this distance by two. Usual pitches are 0.325", 3/8" and 0.404". 3/4" is used for harvester applications, and very rarely for handheld cutting. the pitch of the chain must match the drive sprocket, and the nose sprocket (if fitted).
length: a chain loop must be of an appropriate length in order to run safely. This is described by the number of drive links. This number is determined by the length and type of bar, the sprocket size and the overall configuration of the saw. For replacement purposes, simply count the drive links on the old chain.
Specialised chains
A number of very specialised chain types have emerged over recent years. These include chains made of specilised steel alloys for cutting in extremely cold conditions, chains with tungsten carbide teeth for very dirty conditions and rescue work, ripping chains with altered blade geometry for making ripping cuts, and milling chains for Alaskan mills.