Difference between Rapid, Quiet and Turbine Cut Shredders.
Many thanks who replied to us in our recent request for feedback on your garden shredder buying experiences. I am collating all the responses and hope to share the findings with you shortly.
One question that cropped up quite few times concerned the difference between Rapid, Quiet and Turbine Cut Shredders. It is something I thought we had covered on the web site but apparently not well enough. Consequently I decided to write a short article that addresses just this point.
Definition of a Quiet Garden Shredder
First of all – there is no actual, agreed definition of a Quiet Shredder. It will mean different things to differing manufacturers. Just about all we can assume is that quiet shredders are quieter than some other shredders.
As usual I am going to discuss the Bosch range of shredders. All the other manufacturers seem to employ very similar technologies do the answers should transfer very well.
Why Are Rapid Shredders So Noisy?
The most popular shredder – the results are not even close – are all in the Rapid range.
All Rapid shredders use a high speed electric motor driving a single, high speed spinning blade. The effectiveness of the shredder relies on maintaining the speed of rotation of the blade thereby hitting any waste with the highest possible force. Keeping the blade sharp provides a more effective cut and helps keep the rotational speed high.
High speed motors and spinning blades equates to a pretty high noise level. The Bosch AXT 2200 Rapid is rated at 107dB. This is around the sound level at a middle of the road rock concert. It is well above the danger level.
Why are Quiet Garden Shredders ‘Quiet’?
To get noise levels down the ‘Quiet’ range of shredders uses a quite different shredding mechanism. The high speed motor is replaced with a much slower motor and gear train. The high speed blade is replaced with a relatively slow speed cog wheel.
As waste enters the shredder is is fed onto the teeth of the cog wheel. As the cog rotates it pushes the waste against a striking plate on the side of the shredder. As the wheel continues to rotate the waste is simultaneously crushed and, as the teeth dig in, cut into small pieces.
The gear train is able to generate a lot of torque which helps keep the cog turning pretty much whatever you put into the shredder. The torque and the action of the shredder creates a lot of force which is quite capable of cutting and crushing quite large branches up to about 40mm in diameter. The action of the teeth grabbing woody waste means the Bosch Quiet Shredders are pretty effective at self feeding. Once you feed a branch into the machine the shredder will pull it through.
Of course, the machine has to be quite beefy to withstand the forces generated which accounts for much of the increased weight and price of Quiet Shredders.
So, Are Quiet Shredders Actually Quieter?
The rated noise level of the Bosch AXT 25D is 88dB. That’s 19dB less than the Bosch AXT 2200 Rapid rating.
19dB sounds quite a lot but the decibel measurement of sound is misleading. In fact a 3dB change in noise levels represents a doubling (halving) in sound. 19dB equates to a change in sound level of a factor of 80.
Put another way – the quiet shredders generate 1/80 the sound produced by their more raucous cousins. That is a pretty phenomenal change in noise output.
Problems with the Quiet Shredder Range
Whereas the high speed cutting action of the rapid shredders is well suited to both leafy and light woody waste the quiet shredders only really deal with woody waste. When fed too much leafy waste a couple of things happen:
- a lot of the leafy waste simply drops through
- the leafy waste gets compacted into the valleys between the teeth on the cog wheel. Eventually the cog wheel becomes clogged and stops working.
Clearing the teeth once they have become clogged is a time consuming, tedious process.
Turbine Cut Garden Shredders – All Problems Solved?
The turbine cut range of machines attempts to stay quiet but to deal equally well with woody and leafy waste. In general they are very successful at this but they do cost considerably more.
The shredding mechanism of the TC machines is completely different again.
We again have blades but these are located around the sides of a conic drum. The blade drum rotates between 2 striking plates. Leafy waste drops between the blades and is chopped up by the blades. Smaller woody waste is managed in exactly the same way.
Larger branches are grabbed by the blades and forced against the sides of the side plate. Once the waste is snagged against the side plate the torgue on the blades is sufficient to cut even larger branches – up to 45mm.
The noise level is pretty low too – 82dB. That is something like the sound of city traffic heard from inside a car.
The Turbine Cut shredders are just about the perfect electric shredder. Very quiet, high throughput and can deal with just about any sort of shredding waste. The downside is the cost. At around £400 these cost more than buying a Rapid Shredder for your general garden waste and a Quiet shredder to deal with branches.