4.3.5 – Types of Brush Cutter Blades

On this one page you will find the most complete and detailed information, you will need to choose the

Best Brush Cutter, Weed Whacker Blade


Learn about the different types of brush cutter blades, the good and bad points for each type, to help you make an informed decision when you come to buy a new blade for your brush cutter or weed whacker.

There are basically four types of brush cutter blades; Knife, Chisel, Smasher and Mulching.

And then there is the BrushDestructor Blade, that can replace all of these and do a better job than most of them.

Knife Blades

These types of blades have a sharpened knife edge to the front edge of the blade and cut by slicing through vegetation. It is by far the most common type of metal blade and often comes standard, with brush cutters that come with a metal blade.  There is an almost, infinite number of shapes of knife blades, but what they all have in common is, they are generally lasered or stamped from thin sheets of steel. They range in shape from rectangular to round with dozens of small knife like teeth. The most common is the star shape that have three or four cutting edges, but many of the cheap Chinese brush cutters available on eBay, often come with multiple range of blades ranging from two (rectangular) to forty (like a circular saw blade)

Pros; Cheap, due to being made of one part and stamped out of sheet steel for speed of production. Generally good at cutting soft materials, like grasses and watery weeds. But this does depend a lot on design of blade. Depending on design and quality of steel can generally take a lot of punishment.

Cons; Looses efficiency quickly as the tip of the knife edges dulls. This is because the blade spins at such a speed, that only the very tip of the blade does any cutting. The knife edge of the blade really only does any cutting, when the brush cutter head is swinging fast from side to side. Being a fixed blade, there is no give, when you hit a hidden rock or steel object and with a really hard impact the knife tip will either bend or chip depending on the type of blade and quality of steel. This is why some of the three of four edge blades have a sloping cutting edge. Not to improve cutting efficiency, but to make the blade more resistant to breaking for liability reasons.

Cutting Ability

The number of knife edges, does have a big effect, on how the blades behaves. Knife blades rely on the sharp leading edge of the blade to cut, but since the blade is spinning at around 100 to 120 revolutions per second, only the very outer edge generally does any cutting.

Now if you can imagine your brush cutter head swinging from side to side, it is the speed of the swing that will govern how much of the knife edge is exposed to the new grass. Swing very slow and only the very tip of the blade does any cutting. Swing very fast and more of the cutting edge cuts grass. Now consider a rectangular blade with two cutting edges, that is spinning at 100 revs per second, that means that a cutting edge passes the same spot 200 in one second. Lets say you swing the brush cutter 1m sideways in 1 second. This means that only the outer 5mm of the blades actually cuts new material. With a 4 edged blade, only 2.5mm of the outer edge cuts and an 8 edged blade only 1.2mm of the outer edge cut any grass.

So as you can see, not much of that knife edge actually does any cutting. Now go to a 40 tip knife blade and each blade is only cutting fractions of a milimeter. So as with a nylon line, it is only the very outer tip of the blade that actually does any cutting.

This small knife edge tends to blunten very quickly and so ends up smashing its way through vegetation, meaning that a knife blade very quickly becomes a smasher blade. It is only when this happens and the rough un-cut vegetation that bounces back up under the blade, or when cutting in a vertical motion that the inner knife edge does any cutting. A blunt knife blade, is one of the main reasons for users to develop the habit of revving the brush cutter to full revs and throwing the blade into heavier vegetation and this becomes a habit that is hard to break, when swapping to a chisel or saw type blade.

I had found that when using these blades in the past, the two and three bladed models cut the best for the longest period of time, but this came at a cost.

As these blades being rectangular or star shaped, also tend to drag grass to the centre and wrap it around the gear head. This means that for star blades, you need to keep the brush cutter screaming a full revs, to throw the longer grasses out before it get a chance to start wrapping around the gear head and even this is not always successful with the long tougher grasses.

The multi tip blades become less efficient just as quickly as the tips loose their edge, but at the same time, because of its more round shape, drag the grass around the outside of the blade and so are far less likely to cause long stringy grass to wrap around the gear head.

This is why, different blades are better for different types of vegetation and why many brush cutters come standard with a range of blades. If you only have one type of vegetation in the area you are trying to clear, then this is not an issue, but it becomes very painful if you have to keep changing blades all the time to suit different type of vegetation in a small area like that found on our property.

Mulching Ability

Again the rectangular and star shaped knife edge blades are the best for mulching, when moving the blade vertically through the vegetation, as these blades present the largest knife area to the vegetation.

The Airecut Blade, made by a fellow Kiwi, is by far the best knife blade for mulching and in fact would probably be better qualified as a mulching blade. However, everything comes at a cost and with this blade you will end up wearing a lot of what you cut, as it throws a lot of the cut material into the air. As tough as this blade is though, it is not indestructible and bad cutting practices developed using a blunt knife blade can lead to breaking the ends off of this blade. As unlike a flail type blade, there is no give in a fixed blade and when you hit objects hard, sooner or later something will give.

The rounder shape, multi tip knife blades, with much shorter knife edges, are pretty much useless at mulching and there is not much more that can be said them with regards to mulching.

Chisel Blades

These types of blades have a sharpened teeth around the perimeter of the blade and cut by chiseling through or shaving their way through vegetation. All of these blades are circular with varying number of teeth around the perimeter. These teeth can be part of the blade and have a bent offset for blade clearance, or have chain saw type blades, either riveted to the disc, or an actual chain saw blade riveted between two discs. Most now are tungsten tipped, as the price of these blades have come down considerably price over the years.

Pros; Are more efficient at cutting, as the cutting edge is around the exterior, where the real contact with the material being cut is. Good at cutting hard materials, like woody weeds and hard woods.
Cons; Are generally more expensive, because of there more complex shape and require extra machining to bend, sharpen or attach extra parts. Because the cutting edge is at the tip, it is subject to more impact and wear damage.
These types of blades require sharp teeth to cut efficiently and so are thrown away as many of these types of blades for the average users, are difficult or even impossible to sharpen.
The deeper the cut, the more likely the blade is to bite in and kick one way or the other. The more teeth the blade has, the further it will kick as the blade tries to run out of the slot.
The deeper the cut, the more care must be taken to hold the blade straight, twisting one way or the other can cause the blade to bind in the cut in a serious kick back.

Cutting Ability

Most of these types of blades are extremely good at horizontal cutting, up to the the maximum depth that it can cut. Generally cutting any branches larger than 50 to 60mm in diameter and the speed of cutting slows down very quickly.

This is because, most brush cutters are designed for line cutting that requires high tip speed for a nylon line to smash its way through vegetation, they are not geared for high torque like a chain saw. With a multi tooth saw type blade, the deeper the cut, the more teeth that are cutting, the greater the drag. This means they require much more power and torque to drive and so are more suited to larger machines.

The biggest issue with a round saw type blade as you cut larger diameter branches, is that you have an increasing number of teeth all cutting at slightly different speeds and depth. This is due to the rotation of the blade and the direction the blade is moving in. So as the blade is moving in the direction of cut through a branch, some teeth are cutting into the direction of travel and into the wood. While some teeth are cutting across the wood and some teeth are cutting opposite the direction of travel and out of the wood. This means that as the cut gets deeper, the chances of the blade being kicked in one direction or the other, increases to the point where it is very hard to control the blade.

 

Unlike a bench or skill saw where the teeth are cutting in the direction of travel and dragging the material against the table surface that holds the job from bouncing away. This allows the teeth to bit in and pull itself into the wood as you can see in the moving image below.

To see more on the BrushDestructor Machine

With the exception of the BrushDestructor Clearing Machine, no other brush cutter has such a guide surface. So for any other brush cutter, it all depends on how steady you can hold the end of the cutting head and what quadrant of the blade you are cutting. This means that these types of blade can suddenly bit in, causing the blade to kick violently. It is like dropping a skill saw into a piece of wood to start a blind cut and trying to hand onto it.

Mulching Ability

These types of blades, are generally very poor at mulching, as the large round disc, does not move up and down easily through bush.

Types of teeth

Generally there are three types of teeth that can be found on Chisel blades. There is the one piece blades, where the teeth are the same material as the whole blade and generally have an offset to give some blade clearance when cutting through green timber. There is the chainsaw type teeth, that is either riveted to the main disc, or an actual chain saw chain fitted around and between two discs. And then there is the Tungsten Carbide tipped blades with these tips brazed to the disc.

Steel Teeth

Which were once the most common, are probably the least common now. There are some cheap blades on eBay that have no offset to the teeth, this means that they bind easily in wet sap timber and I would not recommend ever buying one.

By fare, the best steel blades are those that have a good offset, have a tooth that resembles a chain saw blade and can be sharpened with a chain saw file, like this one shown below.

If you decide that a chisel type blade is what you need and you are prepared to keep them sharp, than this is what I think is the best blade by far. The major brands of brush cutters all offer this type of blades as an option. It is just a shame this style of blade does not come with fewer teeth.

Chain Saw Teeth

Blades, have an actual chain saw blade, riveted between two steel discs.

Or the other type is where chain saw teeth segments riveted directly to a single steel disc.

Forester also makes a tungsten carbide tipped chain saw type blade and this can be be sharpened with a diamond file.

Due to the wide width of the cut and the inappropriate gearing of most brush cutters, these teeth need to be kept very sharp to cut effectivly. With a little practice, this is fairly easy to do with a standard chain saw file.

I used one of these for a short time and found that they do cut well, but my brush cutter the time was really underpowered to drive it effectively. I also found that they are only good for cutting tree trunks well above ground level. Use them anywhere near the ground where dust can sand blast the tips, or dig into the ground and with the tip speed these blades are doing they loose their cutting edge very quickly. Unlike a chain saw, which has a tip cutting speed, a fraction that of brush cutter blades.

This blades are even more prone to the same kick back issues as the steel blades, because of the very wide cut of the chain teeth. However this wide cut does give is plenty of clearance and a lot less chance of the blade binding, if you twist the brush cutter when doing a deep cut.

Tungsten Carbide Teeth

Blades, have tip of tungsten carbide welded to the tips of the steel teeth. Tungsten Carbide is one of the hardest alloys known, it can hold an edge really well and can withstand tremendous impact loads, like this found in masonry drills.

These blades are becoming more common as their price is now about a quarter the price of the first tungsten blade that I bought when they first came out. These first blades, cut really well, but did not last long, as it did not take long to rip half the teeth off when cutting through thick branches.

Just a slight twist of the brush cutter, or the sapling started to fall and bind up the blade and off they came.

The only blades to get now, are those that have the teeth embedded into the steel and not just welded to the front face of the steel tooth like that shown above.

However, even though these early issues of the tips coming off have been solved, theses blades are not indestructible. As hard as this alloy is when subject to low speed impacts, it becomes a lot more brittle when facing the high impact speeds that are found when used on brush cutter blades. Depending on blade diameters, tip velocities range from 300 to 450 km/h (180 to 280 miles/h). Hit a hard rock with no give at these speeds and one or more teeth will most likely chip.

 

I think in the early days, they used the same teeth as those fitted to skill saw blades, which had a much steeper cutting angle, as you can see below left. However when used on brush cutters with double the velocity of a skill saw blade and hitting rocks and metal fence posts, this steep angle made them more prone to chipping. The newer blades are much more robust, with a greater cutting angle aproaching 85 degrees and welded all round. 

But with the dusty Australian conditions combined with the very high tip velocities, it does not take long for dust sitting on plants to polish an almost imperceivable 0.05mm radius to the cutting edge of even this super hard alloy and you will quickly find you are trying to burn your way through the timber. Whereas a not as hard, but tougher steel blade as shown on the right, with a much steeper cutting angled cutting tip, can have a 0.05mm polished edge and still cut fairly well.

Number of Teeth

In many reviews, you will read that more is better and if your reasoning is how many tips can be knocked off or chipped before a blade become useless, than more may be better. 

But if you are looking to get the maximum efficiency from the power and very high gearing of your brush cutter, than less is more and I would go for the blade on the right every time. This applies to all of the three types of blades, the less number of teeth the better.

When cutting into small diameter sapling, larger number of teeth are not such an issue, but start cutting into a larger diameter saplings and having just one tooth in the wood at a time means there is no loss of power. The down side of less teeth, is that if you chip a tooth, the performance and smoothness of cutting dropped off very quickly.

The number of teeth can also effect how long your blade cuts well, before it is perceived to be blunt. Where you really need chisel type of blades the most, is when cutting sapling 50mm (2″) and above, but in the case of brush cutters more teeth is less. This is because, the length of the brush cutter shaft, means you have reduced leverage and can only apply a very limited side force to the cutting teeth. This was one of the reasons for changing from 4 teeth on the model-11 flail-blade, to 1 tooth from the Model-14 flail-blade going forward. Going to just one tooth per flail-blade, gave a huge improvement in cutting efficiency.

Difference between the old and new BrushDestructor Blade

Have only 1 tooth cutting, with all the force going into that one tooth and a 0.1mm polished edge does not have too much affect on its cutting ability. Have 10 teeth cutting with a 0.1mm polished edge, with 1/10th the force applied to each tooth and you just cannot push hard enough to get all of those teeth to bit in. Before you know it, you are trying to polishing your way through, keep it up and you are burning your way through. Persist long enough and the heat generated will melt the brazing that holds the tungsten teeth on, leaving you wondering what happened to those teeth. Been there, done that.

Again this leads to the same bad practice that you see so often on YouTube, rev the shit out of the brush cutter and then throw the blade at the branch. You can loose teeth that way as well.

I finally see that one Australian manufacturer has the sense to make a blade with less teeth,

I think you will find that this trend will increase as more people go into shops asking for blades with less teeth now that they are more informed.

Finally it looks like Shindaiwa has listened to what I have said and come up with their LESS equals MORE Tornado 3 and 6 group toothed brush cutter blades.

NOTE; they even say that it results in smoother, faster cut, with reduced kick back and less fatigue. Which means you do not have to push into the job as hard, GOOD FOR THEM.

Smasher Blades

These types of blades have no sharp edges and generally rely on their thin thickness and weight of the pivoting blade or chain to smash through vegetation. These are generally pivoting flail type blades, linked metal blades and a range of different types of chain.

However, because of the EU Directive, where non manufacturer’s spec blades can be fitted to a brush cutter in EU Member countries, many of these blade are no longer available, which is probably a good thing. I am guessing here, but I think many of the one piece knife type blades, end up as smasher blades, if the knife edge is left to wear completely away.

Pros;

Maintains its set set design efficiency, without any need to maintain an edge. 

Generally works well with soft grasses and watery weeds.

Cons;

Generally more expensive, due to being made of multiple parts.

Many are not made of suitable materials to withstand the extreme loads and so often have a short life expectancy.

Generally only good for grass and water weeds, prolonged smashing against woodier weeds will result in early failure.

Some, like the chain link blades, have very high drag and so consume large amounts of power just to keep rotating at a high enough speed to smash vegetation effectively and so are more suited to higher powered machines.

A Chinese copies of these chain blades are still being made and some person is importing and selling them on eBay here in Australia. All I will say is that I would never buy one and I recommend you do not either.

Cutting Ability

There are only a few flail type smasher blade still on the market that I know of, one of them is the Australian made Weedwakka blade. For grass and watery weeds, this blade is very effective, but try to cut anything harder and you will end up trying to burn your way through. This is because, there is not enough mass to its flail blade to punch through denser weeds and so they just keep getting flicked back out of the way.

I personally have used one of these blades for some time, before I decided to make my own brush cutter blade and it was this blade that convinced me that a flail type blade was the only way to go. This blade is great for grass and light watery weeds but the light weight flail-blades just did not have enough weight and punch for anything heavier. I wanted one blade that did everything and at that time, there was not such thing, hence the need to design my own blade.

Mulching Ability

This blade is good for mulching grass and watery weeds, anything harder than that and it just does not have the punch.

Mulching Blades

I have personally never seen or used one of these mulching blade and so cannot speak from experience here. At some stage I will buy one of these blades to try, but until then, if you have any experience with these blades, please let me know your thoughts on them.
Pros;

I would imagine they would do a very good job of mulching leaves and small branches.

Cons;

Would require a lot of power to drive and so would only be suitable for larger machines.

Would feed a lot of impact shock back into the brush cutter again being the reason that they would only be suitable for larger brush cutters.

Possibly throw a lot of material out with considerable force.

Now lets look at the

BrushDestructor

4 in one blade

Please look at this video to see how the BrushDestructor Blades, can easily be used as a smasher blade, a knife blade, a chisel blade and a mulching blade, depending on what you do to the flails-blades.

Pros; This one blade replaces the need for all other nylon line and metal blades. Is a knife, chisel, smasher and smasher blade, depending on how you do or don’t sharpen the flail blades. Designed and build to give long life. Runs smoother than fixed metal blades as flail-blades will absorb a lot of shock. Short term flywheel power reserve from the heavy hubs. Less kick back than fixed blades. Very easy to keep teeth sharp. Does more, with less power than most other blades and nylon line heads.

Cons; Very Expensive. Requires Regular inspection and pivot bolts need to be sprayed with oil after each use. Requires regular sharpening to get the best from this blade, when used as a chisel blade.

Conclusion

I should point out here that I am obviously very bias and you should take what I say here as such. When I want to buy anything online, I do my research, visit a number of sites and always search for bad reviews. Human nature dictates that we are more likely to go out of our way to report a bad or negative review than a good review.


This page was created to answer a large number of questions I have recieved from people inquiring about blades in general, why should I spend this sort of money on your blade, when many brush cutter come supplied with metal blades, why my metal blade does not work as well as expected, Why buy a BrushDestructor blade when I can buy three different blades to do the different jobs, for half the price on eBay, why don’t you make a tungsten tip flail blade and these are just the questions that come to mind.

To write this article, I dragged all the old blades I had rusting away at the back of the shed, to reuse so as to evaluated them based on the knowledge I now have after years of developing and improving the BrushDestructor blade.

Some did a reasonable job, some were very good at doing one thing, some were pretty useless and some were down right scary. All will now go to the tip for scrap metal.

With the exception of the WeedWakka blade, all the fixed blades gave kick back, that I was no longer accustomed to and no longer want to be accustomed to.

The Sharpened steel teeth and sharpened chainsaw blades cut much faster than the BrushDestructor blade up until about 40mm in diameter when the multi teeth started to cause too much drag and kick back issues. However the diameter where this slowdown starts to occur does depend on brush cutter size and power. Try and cut down 100mm to 200mm saplings that I am use to dealing with and they were down right scary as to how much kick back you could get from them.

Nylon lines and blunt blades work as smasher blades and rely on shear velocity to smash their way through grass and weeds. Grass and watery weeds are very tough and flexible and will bend out of the way when hit at low velocity. Hit that same grass at a much higher velocity and it is unable to give way and bend quickly enough and will start to be torn apart. Hit it at very high velocity, and grass will act as if it were frozen and will shatter at the impact point.

Lets look at my small 25cc 4 stroke Husqvarna brush cutter, that has a gear ration of 1.46 which means that the output speed at the gearhead is almost 75% of engine speed. Maximum engine revs is 9,000 rpm and the gearhead speed is 6,165rpm. The nylon line head has a max. diameter of 440mm and at full revs the tip speed on the line is 510km/h. Generally the largest diameter knife blade is 250mm in diameter and this give a tip speed of 290km/h, so as soon as it gets blunt the low tip velocity makes it pretty useless at smashing grass.

The new Model-17 BrushDestructor blade now has a smaller cutting diameter of 300mm, which results in a lower tip speed of 350km/h. But even though it has a much lower tip speed to a maximum length nylon line, the velocity is still high enough to smash grass. Thanks to the mass of the metal blade, whereas a nylon line has a very low mass and so must rely on a much higher velocity to transfer the same energy into the impact point. Try and smash the long string grass you see in the video above and you would be wearing away line very quickly, a blunt knife blade does not have the critical velocity to effectively shatter this grass, yet a blunt BrushDestructor blade does.

  My Recommendations;

If you only have to deal with grass and watery weeds, the Weedwakka or a good quality three edge knife blade is all you will ever need.

Very wet or thick grass and dense weeds and sapling less than 20mm the Airecut blade is brilliant.

Small sapling less than 50mm, you cannot beat the cutting speed of a good brand name steel tooth blade, that you can sharpen yourself with a chain saw file. But keep an eye on the chain saw type blades, when a manufacturer finally comes to there senses and makes a 300mm (1′) diameter blade with 3 or 6 teeth on it, then this will be the best blade. You will then have the power to drive it properly, without owning a monster machine and it will give a wide enough cut, so that wet sapwood doesn’t bind up your blade as easily as the other chisel blades.

If you have a larger property with a wide range of weed and plants to deal with, the versatility of a BrushDestructor blade will pay for itself many time over, even at the price.



 

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