The K-Zone: The real man's gardening tools: the chipper/shredder

A chipper is a machine for turning wood (branches, cuttings, sapplings, woody bramble) into mulch. A shredder is a machine for reducing bulky, green, perhaps wet organic material into compostable shreds. Some machines are capable of carrying out both functions, sometimes simultaneously, sometimes by changing blades or attachments. Although the functions of the chipper and the shredder are similar, you do need the right machine/blade/attachment for the job in hand if you want to get reasonable productivity. Both machines are capable of turning human limbs and digits into fertilizer very rapidly.

In my experience, petrol-engined chippers are overwhelmingly more useful than electric ones, and probably aren't any more dangerous in themselves. Electric machines are fine for dealing with leaves and general garden waste, but woody material is usually beyond them.

Disclaimer: this article is in no way a substitute for formal training, and in no way do I condone the use of powerful and dangerous equipment by incompetent, untrained operators. As a minimum, you should read the instructions and safety information supplied with the machine, and wear suitable protective clothing.

Primary dangers

A chipper/shredder contains steel blades or flails that spin at high speed. Needless to say, any body part that comes into contact with the cutting machinery is a gone'er. Material can be ejected at high speed from the feed openings, as well as the output chute.

Secondary dangers

Petrol-powered chippers are very loud, and often used for long, uninterrupted periods of time. Hearing damage is therefore a real possibility. The engine will become very hot during extended operation, and is usually in an exposed position. The machine itself is likely to be very heavy -- even the smallest petrol-engined machines usually weight in excess of 150 lbs -- and can fall on the operator.

Safety tips

Use protective clothing, etc
Hearing protection is essential, and eye protection highly advisable. Most operators use goggles or safety glasses. Gloves are advisable when handling spiky material (thorn, bramble), and will provide a measure of protection against being burned by the hot engine; but no gloves will protect your hands from contact with the blades.

Keep fingers clear of the blades!
Obvious, really. For pushing material into the machine, use whatever tool is supplied with the chipper. If none is supplied, use a stout stick.

Bear in mind that the feed mechanism can snatch
When using a downwards-feeding hopper, be aware that the blades will snatch at the material fed into it, and drag it into the cutting chamber with alarming speed. Spiny material can catch on the operator's clothes, and drag the operator towards the hopper. It's just about possible that your hands could be pulled in, with catastrophic results. So you should drop material into the hopper, and then prod it down with a tool or a stick, rather than pushing it into the hopper with your hands.

Make sure the machine is stable
You really don't want it to fall on you. A heavy-duty, petrol-engined machine will vibrate sufficiently to wander around on a flat surface, so you may need to chock it into position.

Keep your hands and face away from the places where material is ejected
Naturally, material will be ejected at some speed from the output chute; but most chippers are capable of firing material backwards from the feed hopper as well. This is particularly common if the chipping chamber fills up with un-chippable material, or if the output chute gets blocked. Some machines have gates or flaps to minimize the likelihood of material being ejected backwards towards the operator.
Bear in mind that material can be ejected from the output chute at unexpected times. Material can get stuck in the feed hopper, and gradually slide down into the cutting chamber by vibration. When this happens, chippings will be ejected without warning. A particular risk, on machines that have a collection bag, is that this unexpected activity will happen when you're right in front of the output chute, emptying the bag. So switch off first.

Exercise caution when unclogging the machine
A properly operated chipper or shredder should not clog and, apart from maintenance, it should never be necessary to put your fingers anywhere near the blades. If you have to get your hands in the cutting chamber, ensure that the machine is made safe, using whatever method is supplied (switch off, disconnect spark plug, etc).

Getting good results

Know the limits of the machine
My chipper can take material of up to half an inch diameter in the feed hopper, and two inches in the chipper funnel. This is because material in the feed hopper can fall between the blades and jam them, while the chipper funnel puts materials at right-angles to the direction the blades spin. Anything that will fit into the funnel, even with a shove, will chip fine. But material that goes in the hopper, and is too large, can easily stall the engine, and require manual de-clogging.

Don't put wet, leafy, or green material into a chipper
This kind of material requires a shredder, or a chipper with a shredder attachment. You may get away with chipping a small amount of such material, but eventually the machine will clog. Even if it doesn't clog, the cutting chamber can fill up with un-chippable material, which impairs efficiency and causes back-ejection of material. Freshly-cut prunings of coniferous trees present a particular problem. There's plenty of woody material there, but there's a large volume of green needles. My machine will chip this stuff, after a fashion, but periodic un-cloggings are necessary. In my experience, the usefulness of the chippings produced is so low that it's easier just to dispose of this kind of material by burning it.

Feed material at an even speed
The chipper will have a limited chipping capacity, determined by the engine power and the speed the blades rotate. If you try to feed woody material into the chipper too quickly, most likely the engine will stall (which will do it no good). Most petrol-engined machines have a speed governer, which opens the engine throttle when it senses the engine speed reducing (when the machine is under load). You'll probably get best results if you feed material at such a rate that the engine is running at just under full throttle. On my chipper, the throttle is visible, so it's not difficult to tell when this point has been reached.

Decide whether it's more efficient to move the chipper to the work, or the work to the chipper
If your chipper has a collection bag (or if you have a wheelbarrow and a shovel), you can do the chipping near the pile of material to be chipped, and carry the chippings away. Alternatively, you can put the chipper where you want the chippings to go, and drag the material to the chipper. It is nearly always more productive to put the chipper near the material to be chipped, and carry it away in bags. This is because chippings are very compact, and a great deal of woody material will be accomodated in the collection bag.

Cut branched material into straight(-ish) pieces first
Unless you have a really heavy-duty chipper (the kind that needs a vehicle to tow it on site) you won't be able to put heavily branched material directly into it. If the branches are thin and flexible, you might be able to force the whole thing into the chipper funnel by brute force, but you run the risk of forcing your fingers in too, if you're not careful. It's easier, and safer, to trim the material into relatively straight pieces first. A long-handled anvil lopper should be able to cut material up to about an inch thick, and it's much quicker than sawing.

Decide whether it's worth the effort
Chipping is a good way to dispose of waste woody material. It produces a useful product, particularly from hardwood material. The chippings can be used for surfacing paths, parking areas, and play areas, as mulch and compost for gardening, and even as a heating fuel. But chipping isn't the only way to dispose of waste wood. You could burn it, for example, or just leave it in a big pile to rot (which will take several years, or longer if there are thick tree branches). My experience is that, as a disposal method, burning is at least ten times quicker than chipping, is inexpensive, and requires no maintenance of machinery. Moreover, you can burn stuff that is problematic for a chipper -- bramble, for example. Consequently, I now only chip material which produces a useful product with little work -- pieces of wood that will feed straight into the chipper funnel, are completely free of leaves and needles, and are in excess of half an inch thick. Everything else goes on the bonfire.