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Understanding how impact garden shredders work is a great asset in your search for the garden shredder that is right for you and you garden.

Impact Shredders – Cutting Mechanism

The mechanism used by an impact shredder -also known as rotary or rapid shredder – is the simplest of all garden shredders.

Impact shredders use a high speed – 4,000-4,500 RPM, rotating blade.  When you feed your garden clippings through the shredder they are presented to the blade.  The blade chops away until the clippings are reduced to chips.

A sample Impact shredder blade used to show how impact garden shredders work
Impact Shredder Blade

Clippings may not be cut through in one pass.  The high speed blade hits the clipping so hard that chips fly off.  Hitting the cuttings quickly and often creates lots of chips and soon reduces the clippings to chippings. 

In many ways, the more American names – Garden Chippers or Wood Chippers – is more appropriate for impact shredders.

Efficiency of Cutting

The efficiency of the shredder depends on:

  • how sharp the blades are
  • how quickly they are rotating
  • the effectiveness of the motor to keep the blades turning.

The first 2 factors need little explanation -sharp blades, moving quickly, deliver the impact to chop more effectively. 

The last criteria is not as clear cut. 

Whenever the blades hit any waste they try to slow down.  It’s the motor’s job to ensure they keep turning.  That’s all pretty obvious.  However, not all motors and drive trains are created equally.  When the blades hit woody waste there is a tendency for the blade to try to bounce which adds a sort of percussive load onto the motor.  Better quality motors and drive trains are better at dealing with this and continuing to provide the drive to keep the blades turning. These shredders are therefore much less likely to slow down or stop.

Basic Maintenance – Keeping Blades Sharp

To retain a sharp cutting edge and to resist damage from the inevitable soil and stones, impact shredder blades are specially made to be very hard and strong.  Blade manufacturers usually say that the blades cannot be re-sharpened so anything to extend the life of the blades is very welcome.  Many manufacturers make double edged blades so that as they lose their edge they can be tuned over so the second edge now does the work.  Turning blades over is the work of a few seconds and effectively doubles the life of the blades.

Once you have used both edges you will need to replace the blades.  Again, this is a pretty simple operation that only takes a few moments.  Replacement rotary shredder blades seem to cost in the range of £15-25.

Noise Levels

Impact shredders are inherently noisy.  High speed rotating blades are not quiet to begin. When that blade is repeatedly chopping into woody waste the noise levels can be pretty high.  Typical noise levels are in the 105-108dB range.  This is well into the range that can start to damage your hearing. 

You should certainly use ear protection in the form of ear defenders or ear plugs.  If your neighbours are very close to where you are shredding you might like to warn them first.  The sound from a garden shredder really can be irritating on a summer’s evening.

Impact Shredders – Best Used For

Impact shredders are particularly good for cutting up your green garden waste and smaller cuttings and clippings.  They will cut up branches up to 40mm diameter but branches this size make take a while to be chipped away. They are not at their best when tasked with shredding bigger, dry woody waste.  This is much more the province of the quiet, crusher shredders.  So, if you predominantly want to dispose of woody waste, you may well be advised to look elsewhere.

All shredders can be dangerous if not used appropriately.  We have already mentioned using ear protection but you should also use eye protection and gloves.

The shreddings from normal usage are likely to be very fine and will compost very quickly.  If you have done a lot of shredding do take care to mix it with other, more substantial garden waste before adding it to the compost heap.  This should prevent the very fine shreddings forming a seal to the rest of the composting.

Personal experience and a huge numbers of the reviews from across the internet implied that the Bosch AXT 2200 Rapid is the best impact garden shredder you can buy.  In fact Bosch Shredders dominate the whole electric garden shredder market – and for good reason.

Personal experience and a huge numbers of the reviews from across the internet implied that the Bosch AXT 2200 Rapid is the best impact garden shredder you can buy.  In fact Bosch Shredders dominate the whole electric garden shredder market – and for good reason.

 

Bosch AXT 2200 Rapid - Typical example of an impact shredder
Bosch AXT 2200 Rapid – Typical example of an impact shredder