This article was originally published on the web at cranbrookengineering.co.uk however that website is defunct at April 2013. The copyright is with the original owners of cranbrookengineering.co.uk

The story of the chainsaw

According to Wikipedia, a German surgeon named Bernard Heine made a saw for cutting bone in 1830. A chain carrying small cutting teeth with the edges set at an angle was moved around a guiding blade by turning the handle of a sprocket wheel. The origins of the modern chainsaw are uncertain, but Joseph Buford Cox and Andreas Stihl both had a hand in it. In 1927, Emil Lerp, the founder of Dolmar, developed the world's first petrol-powered chainsaw.

Chainsaw design

The environment

These days, a lot of effort is put in to making chainsaws environmentally acceptable. Considering they are so noisy and that they are used to fell living trees, that may sound like a bad joke. Not at all. Tremendous improvements in noise emissions have been made, even down to the most minute detailing of the chain links.

Electric chainsaws are also much quieter than petrol models. How a saw is used is up to the user not the designer: one hopes it is used on sustainable forests.

Engines and lubricating systems are being continually developed to use less fuel and oil. Stihl have designed catalytic converters for some of their chain saws, making emissions harmless (like a modern car). The company has also invented a new type of four-stroke engine which uses a fuel-oil mix, rather than separating them, and which has greatly reduced exhaust emissions.

Features

There are two aspects to the lubrication of chainsaws. One is engine lubrication which is usually achieved with the oil in the two-stroke fuel mixture. The other is to lubricate the chain which would otherwise get red hot. There are subtle design features to ensure just enough of the thick, anti-fling oil reaches the places where it is needed but without waste. Some makers have systems which allow adjustment of lubrication according to how hard the wood is.

The best chainsaws now have foolproof safety features. Kick-back is the dangerous phenomenon caused when a chain tooth jams in the workpiece, the reaction to which is that the whole saw kicks back violently towards the operator. The Stihl QuickStop safety brake detects the rapid movement and stops the chain in a fraction of a second. Other safety features on some saws are a brake that comes on the moment you let go of the rear handle, and a device to catch the chain should it snap. Nevertheless, it is vital always to wear safety clothing (see another article).

Like other hand-held outdoor power tools, the high-revving engine and high-speed chain would cause uncomfortable vibration for the operator if nothing were done. All modern saws provide sophisticated damping to improve comfort.

Saw chain, guide bars and sprockets

It is not generally known that there are many variations of chain design, depending on the application. These examples of Stihl chain are used as follows:

1. Picco Mini and Picco Micro. Low profile for use on light chainsaws and pole pruners. The Mini has very low kickback tendency and is well suited to DIY users.
2. Rapid Micro. All round chain for farming, forestry and building. Easy to sharpen and tolerant of sharpening mistakes.
3. Picco Micro 1 and Rapid Micro 2. Have special safety links and extremely low kickback. Especially suited to tree surgery where the nose of the bar is used a lot, for precision.
4. Rapid Super. Heavy duty chain for professional use.
5. Rapid Duro. Carbide tipped chain for extreme conditions such as soiled wood. Even on gritty wood, life is 10 times longer than standard chain.
6. Rapid Duro S. Reinforced with tungsten carbide and cobalt, these chains are fitted to emergency services saws that cut almost anything.

Guide bars and drive sprockets lead a punishing life and are made of high grade steel, sometimes reinforced with other materials. They are designed in incredible detail to assure correct lubrication. Some guide bars have a slim sprocket at the nose, reducing friction to very low values.

Safety Considerations

Chainsaws cause many fatal accidents every year, so you should buy a modern saw with all the safety features mentioned. Wear safety clothing and get some training in correct usage. Never use a mains electric chainsaw without a safety trip inserted in the 13-amp socket: that way you will not be electrocuted if you accidentally cut the cable. Before commencing a cut, think about how you are standing, and how the wood will move once cut.

Maintenance

All chainsaws come with maintenance instructions. Sharpen the chain teeth with the right size of round file, using a holder to get the angle right and a gauge for the depth. Set the chain tension carefully and adjust it often. Sharpening is skilled work, probably best left to a professional - especially when you consider the dangerous consequences of doing it incorrectly. Electric machines need less maintenance and are therefore cheaper to run than petrol models; but sharpening them is still a tricky job.

Keep the air filter of engines clean: a dirty one causes wear. Be careful to mix the fuel up correctly, and give the chainsaw a shake before using it, to ensure mixing of the petrol and oil. It is a great mistake to keep old fuel as it goes stale within a few months, making starting difficult and gumming up your carburettor. This can be avoided by adding a little fuel preservative, such as Briggs & Stratton make.