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Some hints on buying and using a chainsaw

A chainsaw is a very useful tool for pruning, felling, and cross-cutting trees. It's also useful for some kinds of carpentry: a chainsaw makes light work of cutting joists, for example.

In my experience, petrol-engined machines are overwhelmingly more useful than mains-powered electric ones, because of the extra portability, and probably aren't any more dangerous in themselves. However, battery technology is rapidly catching up, and full-size battery-powered chainsaws are now a viable alternative to petrol -- if you can afford one.

Mains-powered electric chainsaws are, however, much lighter than either battery or petrol models. They might be safer in practice, simply because they don't exhaust the operator so quickly.

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Disclaimer: it goes without saying that anyone who uses a chainsaw ought to have proper training from a competent person. Nevertheless, nobody (with the possible exception of your spouse) will stop you buying a chainsaw from a DIY shop and setting about yourself with abandon; and most chainsaws are supplied with only the most rudimentary instructions.

I do not claim to be any kind of expert on chainsaw operations. What follows is based on my own experiences over the last twenty years or so, and might help somebody just starting out with a chainsaw, and daft enough not to have proper instruction. When I started using a chainsaw as a young man, I was shown how to do it by a friend. There was, at that time, no formal training or certification. Now there is and, if you don't take it, you've nobody to blame but yourself.

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It goes without saying that this article is in no way a substitute for formal training, and in no way do I condone the use of chainsaws by incompetent, untrained operators. As a minimum, you should read the instructions and safety information supplied with the machine: in particular, there will be important information about chain tension, idle speed adjustment, fuel/oil mixture, and maintenance. Bear in mind that there are (in the UK) legal restrictions on the use of chainsaws in the course of business, on land other than your own.

In this article I'm only considering two-handed chainsaws. In recent years there has been an increase in popularity of top-handle saws that can be used one-handed. While I can see the appeal of such machines, I don't own one, and can't comment on their safe use.

A cautionary tale

A few weeks ago I had my first (thankfully minor) chainsaw injury, in more then twenty years of forestry work. I guess I had become rather complacent but, in fact, the risk I put myself in arose before I even started the saw.

I was working in woods with my wife - she was collecting up cut pieces for chopping, and I was felling small trees nearby. Too nearby, as it turned out. I saw her out of the corner of my eye just as a tree started to fall, and I immediately spun around to shout to her. As I did, the saw swung across my legs, and the blade made contact at about thigh height. It wasn't under power -- I had instinctively released the trigger -- but it still bit easily through my protective trousers, and cut a channel about a quarter inch deep and six inches long in my leg.

This was a novice's error, and one that I really should not have made. You need to make sure you know where other people are in relation to where you're working, and they need to know not to approach. I count myself lucky to have gotten off so lightly.

Primary dangers

The business end of the chainsaw consists of a chain of very sharp blades, propelled around a bar usually 14-18 inches long (sometimes longer for specialist work) at high speed by a powerful motor. Most injuries are caused when flesh comes into contact with the moving blade. This may happen because the operator slips and falls on the blade, or simply swings the saw around without waiting for the blade to come to a standstill. A particular concern is the potentially-vicious kickback -- the blade is thrown rapidly backwards when the chain comes into contact with something it cannot easily cut. Most kickbacks are caused when the far end of the chain comes into contact with something metallic, and modern chainsaws are sometimes supplied with a chain guard that fits over the end of the bar to reduce the likelihood of such occurrences. Injuries to the back of the left hand (with a right-handed saw) are particularly common, I'm told.

Secondary dangers

Because chainsaws are typically used for cutting large pieces of wood, there is a risk of heavy objects falling or rolling onto the operator. Chainsaws are very noisy, and hearing damage can result from prolonged use. Some operators experience vibration injuries (`white finger') but these are not so common with modern machines. Because of the direction of motion of the chain, injuries caused by objects being thrown into the operator's eye are relatively uncommon -- but that's no reason to push your luck.

Tripping and falling injuries are common when using a chainsaw -- not because of the saw itself, but because chainsaws tend to be used where there are tree roots and pot-holes. The presence of the saw, particularly if it's running, adds a particular horror to would would otherwise be a minor mishap.

Safety tips

Use protective clothing, etc

It's obvious really, but not so obvious that I haven't seen people using chainsaws with no protective equipment at all. In all circumstances you should wear stout gloves -- ideally specialist chainsaw gloves with a reinforced panel on the back of the left hand. If you're using a chainsaw for more than a minute or so, hearing protection is a good idea. If you're felling or pruning trees, you need a helmet to protect you from objects falling on your head, and steel-toecapped boots to protect you from objects (including the saw) falling on your feet. Eye protection is probably a good idea, although I rely on my ordinary spectacles. Leg protection (chaps or full trousers) is a good idea if you're likely to be cutting downwards. Like many chainsaw operators, I prefer not to wear upper-body protective clothing. I feel that the very real risk of overheating and dehydration with such clothing outweighs the relatively small risk of upper-body injuries. But your mileage may vary. The Health and Safety Executive recommends that all chainsaw operators carry or wear a first aid kit, rather than relying on a first aid post some distance away. Your first aid kit should include a dressing suitable for large wounds -- chainsaw injuries aren't likely to be fixed by an Elastoplast. I have a wearable pack containing a haemostatic bandage that, thankfully, I've never had to use.

From time to time I wear my Kevlar motorcycle clothing when operating a chainsaw. I've even been known to wear a motorcycle helmet when I've been worried about objects falling from above. The body armour will not only offer protection from the saw, I think (hope) it will also offer some protection from impact injures caused by falling objects. It's exhausting and dehydrating, working in such a get-up, but I think some circumstances merit it. "Ordinary" chainsaw safety gear only protects you from the saw, not from secondary injuries.

Don't put your body in the kickback arc

If the saw kicks back -- and it will at some point -- the tip of the chain bar will describe an arc whose centre is approximately at the centre of mass of the saw -- usually near your left hand. If you hold the saw so that you are cutting downwards, with the blade in line with the centre of your body -- which is what most people naturally do -- the tip of the blade will fly towards your face if it kicks back. The way to use a chainsaw that leads to the lowest risk of a kickback injury is to put the workpiece between yourself and the blade. That way, there's nowhere for the blade to kick back to. If you can't do that -- and usually you can't -- stand well to the left of the kickback arc. Then, if it does kick back, the chain tip will end up to the right of your right ear -- still frightening, I imagine, but not catastrophic.

Having said all that, I should point out that kickback risk depends on the size and power of the saw, and the operator's weight and strength. For nearly all my forestry work I use a 14" saw, and I'm a large, heavy fellow. I've (fingers crossed) never so far had the blade kick back more than a few inches.

A well-maintained chainsaw, operating within its design limits, is very easy to use

A well-maintained chainsaw, used properly, with a sharp chain, cuts by itself. If you are cutting downwards, the weight of the saw alone should normally be enough to push through the cut -- you don't need to force it. If you need to push on the blade, or the blade tends to get stuck in the cut, something is wrong -- most likely the chain is blunt, or the cut is closing up around the chain (see below).

Before cutting, think about where the cut piece will fall or roll

Naturally you aren't going to put any part of your body directly underneath something that will fall when you cut it, but you might be surprised how quickly a heavy log rolls away from the trunk it was cut from. If possible, position yourself uphill from any place where falling wood will roll or slide.

A properly-adjusted chainsaw does not turn the chain at idle

A petrol chainsaw should be capable of being left ticking over between cuts. A properly-adjusted machine will not idle fast enough to engage the clutch and start the chain turning. The engine might idle too fast if the choke is open. This is why the instructions supplied with most chainsaws state that, when starting the machine cold, you should close the choke as soon as it seems that the engine will fire. A chainsaw whose chain moves when idling, with the choke fully closed, might need its idle screw adjusted. However, a common cause of this problem is an incorrect fuel-oil mix in two-stroke engines, so it's worth checking this before tinkering with the carburettor. Your really don't want the chain spinning when you're not pressing the trigger.

Electric chainsaws have no need to run between cuts and, in fact, a good-quality one will stop and start the blade instantly as the trigger is operated.

Be aware that trees don't always fall where you want them to

Even if you cut the requisite hinge, there is always a chance -- a good chance, in my experience -- that the tree will fall other than where you planned. Of course, a skilled operator stands a better chance of getting the fall line right than an unpractised one, but it is very difficult to get a leaning tree to fall anywhere other than the direction it is leaning. Generally you need ropes and pulleys to handle a leaning tree that cannot fall in its natural direction.

Know your limits

... and know the limits of your equipment. For my part, I'm reasonably happy to use a chainsaw to fell trees of up to about 16-inch diameter, with a clear line of fall, on flat, dry ground. I won't use a chainsaw on a slope with the work above me, when it is slippery, or above chest height. At my age I certainly won't get up into a tree with a chainsaw, even though I do still own the necessary safety equipment. I don't own the equipment necessary to fell a tree that doesn't have a clear fall line in a safe direction, so I wouldn't attempt this. Finally, if it's getting towards the end of the day and my chainsaw runs out of petrol, I don't fill it up -- I stop work and fill it up next time. This is superstitious behaviour, I know, but it does limit my opportunities for using a chainsaw when I'm dog tired.

Getting good results

When you cut down with the underside of the bar, the saw will pull towards the workpiece

If the work is fixed -- a stout tree branch, for example -- it will pull your arms towards the work. If the work is not securely mounted, the work will be pulled towards you. Even heavy logs can be pulled surprisingly forcefully towards the saw. The amount of pull will depend on the power of the saw, among other things, but could be more than 50 pounds. You can avoid this effect by starting downward cuts with the "dogs" of the saw touching the work, and then cutting by rotating the bar downwards, rather than pushing the whole saw downwards. Of course, if the work is thick, you'll have to push downwards as well as rotating.

In any case, you should usually avoid cutting with the furthest third of the bar, because kickbacks are mostly likely if the tip of the bar snags on something.

If you cut upwards with the top side of the bar, you'll get the opposite effect -- the saw is pushed away from the work.

These push and pull effects are not necessarily a problem, and can sometimes be used to your advantag; but they can be surprisingly forceful, so it's as well to be aware of them.

Petrol chainsaws are designed to cut at full throttle

At full throttle a powerful chainsaw is extremely noisy and smokey, and you might be tempted to regulate the speed (and the noise) with the throttle. Unfortunately a petrol chainsaw is not designed to operate this way, and it won't be efficient or safe. The blade needs to be spinning at full speed before it even touches the workpiece. If it isn't, it will either not cut at all -- because the clutch will disengage -- or it will snag.

When replacing the chain, put it on the bar the right way round!

This seems obvious, but there's nothing to prevent you putting it on back-to-front, in which case it won't cut, and will get very hot. Yes, I've done this. The correct orientation will usually be marked pictorially on the machine somewhere near the bar, but if your chain is sharp, you won't have any problem feeling which direction it should be moving in.

Watch the chain tension

When cutting continuously, the chain will get hotter than the chain bar, and expand more. This means that the chain tension will reduce. If the chain becomes too slack, it can jump off its sprocket, which often means that you'll need a new chain. In any event, there will be a certain amount of downtime. If you adjust the chain tension when the chain is hot, you'll reduce the chain slack, but when the chain cools down it will bind on the bar, and not cut at all. Most manufacturers recommend adjusting the tension when cold, but this means that you'll need to keep an eye on the chain slack when the chain warms up, and either tweak it or let it cool down if the chain starts to hang off the bar. Needless to say, a chainsaw that offers tool-free tension adjustment will provide for easier tension control than one that requires a screwdriver. A new chain will stretch a bit, and therefore lose a lot of tension, in the first few minutes of use.

Before cutting, consider whether pressure will develop on the bar during the cut

Chainsaws are provided with a clutch, to prevent damage to the engine if the chain cannot cut. In general, if the chain becomes crushed between two pieces of wood, you won't be able to power out of it, nor will you be able to pull the saw out of the cut by main force. Instead, you'll have to stop work while you insert wedges with a sledgehammer to free the blade. The problem is worse when cutting resinous woods, particularly softwoods cut in the summer.

All this means that, before you cut, you'll need to think about how the wood will move during the cut. For example, if you are cross-cutting (that is, sawing up) the trunk of a felled tree, and the trunk is propped at both ends on its branches, then if you cut downwards the weight of the tree will cause the cut to close up around the saw blade, and it will get trapped. Instead, if you cut upwards from below the trunk, the weight will tend to open up the cut, and it is less likely to trap the blade. On the other hand, if you are lopping a stout branch from a tree, the weight of the branch will open up the cut if you cut down from above. This creates another problem, of course -- as the cut progresses the weight of the branch will put tension on the remaining, uncut wood, which might tear. The solution is to make a small cut from below, and then cut down from above.

If you don't cut a hinge when felling a tree, try to cut in the direction of the tree's natural angle of fall

It is standard practice to cut a hinge (a wedge-shaped cut-out) in the side of the trunk to control the direction of fall. Any chainsaw should be supplied with instructions showing how to do this. Where the trunk is less than about three inches in diameter at the base, it is not really practical to cut a hinge. It you don't cut a hinge, but instead cut across the trunk in one movement, then one of two things will happen. If you are cutting towards the tree's natural direction of fall, the tree will start to fall as soon as its own weight is too heavy for the remaining wood to support. You might be left with a jagged stump, which can be avoided by making a shallow cut in the other side of the trunk before starting the main cut. The tendency of a tree trunk to tear along its length when felled is called the "barber's chair" effect. I have no idea why.

If you cut against the tree's natural direction of fall, the tree will settle on the blade, and the cut will close up and jam the blade. If you're lucky, and strong, and the tree is not too heavy, you'll be able to put your shoulder against the trunk and push hard enough to open up the cut and pull the blade out. If not, you'll probably need winching gear to free the blade, which is a drag.

Fuel and oil

All the petrol saws I've ever seen require pre-mixed petrol and two-stroke oil. The easiest way I've found to mix the fuel and oil is to buy the oil in individual 100ml bottles. These make up the correct mix ratio for my saw (and most other saws) when poured into a 5-litre petrol can.

You can get fuel-mixing bottles for making up smaller quantities, but I've found them to be more trouble than they're worth. However, if 5L of fuel is much more than you need, it's probably worth using a mixing bottle. I reckon 5L of fuel gets me about 15-20 hours of sawing.

You'll need separate oil to lubricate the bar. Decent chainsaws are designed so that the bar oil is consumed less quickly than the fuel. So if you fill up the bar oil every time you fill up the fuel, you'll never run the saw without lubrication. Like most people who have a respect for the natural environment, I want to use biodegradable oil in my saw. But I often don't, because it's expensive and it attracts rodents.

Maintenance and sharpening

A decent saw doesn't need much maintenance. Occasionally you'll need to vacuum the cruft out of the air filter, and clean the spark plug. In my experience, an expensive saw needs less maintenance than a cheap one. It doesn't hurt to prise the oily wood pulp out of the cooling fins from time to time.

Regardless of the kind of saw you own, the cutting chain will need regular sharpening. I used to run my saws until the chain teeth were as blunt as sausages, and then use a power tool to grind them back into shape. I have two tools for this: a Dremel that I use at home, and a specialist 12V grinding tool that I run from my car battery when I'm in the woods.

There are two problems with this approach. First, at least half the time you're using the saw, you're using it with a below-par chain. Second, the heat generated by the power grinder removes the tempering from the chain. This means that it gets blunt a lot quicker next time.

Using a power tool to sharpen a blade is OK, I think, provided that your don't let it get so blunt that the chain gets red hot when you sharpen it. However, these days I nearly always sharpen my chain by hand with a file.

How often? Every time I use the saw. No exceptions. After an hour of use, it takes me about 10-15 minutes with a hand file to get the chain razor sharp again.

You can buy specialist chainsaw files that have guides to position them correctly on the chain and, for an extra few quid, this seems like a good purchase.

Every so often I'll abuse the saw so badly that I can see that the hand file isn't going to be up to the job. Then I'll use a power tool but, as I said, it's necessary to be very careful to keep the temperature under control. ## Saw choice

You can buy a petrol or mains-powered chainsaw in a DIY store or garden centre for about £80, and it will be fine -- for a week or two. If all you want to do is prune that overgrown tree in your garden, it will last long enough for that.

The problem with these saws -- apart from not being very robust -- is that they're too big. Size sells, I guess, but there have been few occasions where I needed an 80cc engine and four-foot bar for the kind of work I do. These cheap saws are overpowered and very heavy. A heavy saw is tiring to use and that, eventually, is hazardous.

My current saw of choice is a 30cc petrol, 14" model that I bought from a specialist forestry supplier. It was about £400 back when that was a lot of money, but I've used it nearly every spring day for twenty years. I once accidentally left it outdoors for an entire winter, and it still started first time in the spring.

What my saw doesn't have is a self-tensioning or tool-free tensioning mechanism. Considering the time I spend fiddling with the tension adjustment, I'd probably spend the extra money if I were buying a saw now.

In fact, if I were buying a saw now, and could afford it, I'd buy a modern, 14" or 16" battery-powered model in addition to my petrol saw. I'm not talking about the cheap, one-handed 12V units that are sold on eBay, but specialist forestry units. You'd need at least two batteries, perhaps more, because you only get 10-15 minutes use from a charge with these saws. A top-quality battery saw will do most of the jobs that a petrol saw with the same blade size will do, but will be much safer, and much easier to start. That's a consideration at my age.

Of course, a 14" saw won't tackle a sequoia redwood. It won't even tackle the mature beech trees that I need to fell for timber soon. When the time comes I'll need to decide whether to hire a bigger saw, or hire a person to use it. I do a lot of forestry work, but I'm not getting any younger.

[ Last updated Sun 21 Mar 2021 05:31:30 PM GMT ]