This new Model-17 Blade, although at first glance, looks very similar to previous BrushDestructor blades, it has a lot of improvements, as a direct result of lots of feed back from the many current users of BrushDestructor Blades.
This feed back has resulted in a new blade designed specifically to meet the users requirements, a true bottom up design. Meeting all the many requested requirements has resulted in a new model that is;
To withstand extreme punishment required by commercial operators with high powered brush cutters.
Smaller in diameter
By 34mm, due to the majority of sales of this blade now going to residential property owners who are buying this blade and who’s brush cutters are generally 30cc or less.
Being smaller in diameter will also allow it to better withstand the extreme stresses from high powered machines, that can maintain high speeds under while under high loads.
By 22% than the previous model-16 blade, again making it more suitable for the lower powered machines and to make it that little bit easier on commercial operators who have to swing a brush cutter around all day.
Below is a drawing comparing the new Model-17 blade to the older Model-16 blade and below that is a more detailed description of what has changed and what is new.
Top and Bottom Hubs
Have been made smaller to reduce the centrifugal stresses on the hubs. This also makes the blade lighter and more easily powered but smaller brush cutters. The number of Anti-Fouling-Blades have been reduced to three, the slot opening size have been reduced by a third and the slot location have been moved to put more metal where all the high tension loads and bending stresses are. This results in a hub that is considerably stronger than the previous model.
Have been made smaller and lighter to help reduce the overall weight of the Blade and the back edge redesigned to reduce the impact loads to the rubber impact stop.
Are considerably more efficient at clearing away stringy grass and vines, even though they are a third the size and there are now only three anti-fouling-blades instead of the six found on the previous model. After carefully studying exactly how these long grasses start to wrap around the gear head, this new design shreds the grass as it is starting to pull tight around the gearhead and directs it over the top of the gearhead and guard. The previous design tried to wind the grass away from the gearhead and under the guard.
Below you can see how long wet grass, has not been able to wrap around the gearhead and stall the brush cutter, which used to be a major problem when I was using a line triller.
Bush Bolt Assembly
Has changed to reduce surface contact area of the side bearing faces on the nut, bush and bolts. This is to help reduce the pivot bolt assembly from seizing up, as a result of plant sap getting between the very close bearing faces and being allowed to dry. Generally a spray of CRC or Silicone lubricant after each use, will prevent the sap from drying out and allow the pivot assembly to rotating freely, unfortunately it is easy to forget to do this.
New Nut Guard
Is now included and become an integral part of the design improvements. The inclusion a custom designed nut guard, has allowed the removal of the large hole opening in the bottom hub, that has been the weakest link in the design right from the very first Model-10 Blade.
This nut guard, is made from the same grade and hardness of steel as the flail-blade pivot bush, to give a very long life.
New Rubber Spring Washer & Impact Stop
Replaces the steel spring washer and the need for the Anti-Fouling-Blades to act as impact stops for the flail-blades. The design and search for materials has been one of the biggest challenges faced to make the model-17 blade stronger and tougher than any blade before it.
This model has taken more time, more prototypes, more testing, more punishment to machine and more costs than all the previous models before it combined.
I recommend that you scroll further down this page to read more about the development and testing that has gone into making this blade what is is now.
Due to the extra two expensive parts that have been added to this model blade and the shear time and number of prototypes involved, to meet all the goals to make this the best brush cutter blade in the world. Unlike all earlier models, where I personally carried the cost, this will the first blade, where the actual development cost are being amortised into the cost of the blade. The recouping of this cost, will then go into the development of the BrushDestructor Clearing Machine, which is going to require considerable capital to make a reality. Your support, by buying this blade, will help make the new BrushDestructor Clearing machine.
As I have said elsewhere, it is the blade that is the business end of any brush cutter. All the brush cutter does, is provide the power and direction. Pick any brand of brush cutter and you will get more done with a 25cc model & one BrushDestructor Blade than with a 50cc model using the manufacturers multiple range of blades and still be cheaper off.
Right from the very start, the ability to do the job the BrushDestructor blade was design to do with ease and safety has always taken priority over cost and that requirement has not changed with this blade. If you should have doubts that this blade cannot possibly be worth this price, please take a read through the Customer Reviews Page.
I would like to add here, that I make no apologies for the high price of this blade. It has been designed and built to do a very demanding job, while requiring very low maintenance and with the exception of the replaceable flail-blades should out last most brush cutters.
This blade does not mind if it is being driven by a cheap Chinese brush cutter that cost less than it does, or by a $1000 plus commercial machine, the results are the same and only the life expectancy of the brush cutter will be at question here, not this blade.
The Model-17 Blade is available in four options, click photo below for more option and purchase details.
Development & Testing
The development of this Model-17 blade, has taken the longest time, with the most number of prototypes and is the most expensive so far to date. Below is the story of all the prototyping and testing I did until I was 100% happy with its performance and toughness.
One of the greatest weaknesses right from the very first model-10 blade, has be the large opening in the bottom hub to accommodate most the different sizes of nut guards that come standard with the wide range of brush cutters.
It is this large opening that has created a weakness in the bottom hub for all the models till now and although the number of failures of the bottom hub has been extremely small. There has never been a failure of the top hub which would mean the completer failure of the whole blade. However, as far as I am concerned, any failure of a hub is unacceptable.
The obvious solution here was to supply a much smaller nut guard as a standard part of the blade and so reducing the large opening in the bottom hub. Move the Anti-Fouling blades so that they no longer act as an impact stop and include a rubber impact sheet sandwiched between the top and bottom hubs as can be seen below to absorb the energy of the flail-blade flicking back.
I spent a lot of time researching all the different types of rubbers that could withstand high impacts and found one that was used to line the blades of snow ploughs and tip trucks to prevent ice from sticking to the steel in the northern US States and Canada. Below left, you can see how the rubber was supposed to prevent metal to metal contact between the Flail-Blades and the Anti-Fouling blades that results in high shock loads transferred to the hubs.
Unfortunately, as tough as this rubber is at withstanding high impacts, it proved to be very weak under tension loads. It took less the 30 seconds at full revs for the rubber to rip itself apart from its own weight under the high centrifugal loads as you can see above, before I even had a chance to test its ability to withstand the impact loads. Never did find the other bits of rubber.
Once the rubber was gone, the flail-blades quickly sheared their way through the anti-fouling blades and started impacting the custom designed nut guard.
The flail-blades were now free to hit one another, with the resulting damage after a very short time of use and rendering the blade inefficient at cutting anything.
Below you can see the damage that was caused to the nut guard now that it was acting as a stop for the flail-blades.
This guard was made from the same steel and heat treated to the same hardness as the the grade 12.9 bolts, so it gives you an idea of the forces involved when a flail-blade is flicked back after an impact with a solid object. It should also give you an idea of the energies involved that a standard supplied fixed metal blade is also subjected to and which has to be absorbed by the brush cutter.
I then tried a fibre reinforced conveyor belt rubber, but because of the design of the reinforcing fibre weave, all these rubbers are very strong in tension in one direction and not in the other. Under high centrifugal loads, this resulted in no stretch in one direction and a lot of stretch in the other as can be seen in the photo below where the stretching rubber polished away the plant sap. What was even more amazing, was how much vibration the stretching rubber caused.
I then made a mould to press my own reinforced rubber with three layers of fibreglass cloth laid at 120 degrees to each other. The fibreglass cloth turned out to be a too tight a weave and it quickly separated into three seperate layers after only a couple of minutes.
I then found a loose weave dyneema fabric, again laid in three layers a 120 degrees to each other. It actually worked very well, but eventually started failing after a couple of days of hard use.
In the close up below, you can see how the compressive impact shock waves were blowing the rubber away from the reinforcing fibre.
Finally I found a rubber that would do the job, it is the hardest version of synthetic rubber that is used in suspension and shock absorber bushes in cars. It easily pours into a mould as a liquid and can be cast into any shape, but to get the hardness I require the rubber has to cure under very high pressures and with this first prototype only the first sample came out of the mould to match the thickness tolerance I required. Because of the large flat surface and pressures involved the mould was not strong enough and quickly distorted from the high pressures.
The video below shows the extreme testing this blade was put through, to see if this rubber could withstand the punishment and as you can see in the video and close up photos it survived the test unscathed. Unfortunately the brush cutter did not fare so well.
I can tell you one thing, I would not want to be standing anywhere in the vicinity of this test if I was using a standard supplied three star blade as I am fairly certain that it would shatter and explode parts of the metal blade in all directions.
It was at this point that I thought the design was finalised and was gearing to go into production when I received three emails in close succession about how amazing the blade was but it would be better if it was a just that little bit lighter.
So I decided to make the blade a bit smaller in diameter, which would reduce the stresses on all the parts. Making it lighter, would also make it better suited to lower powered brush cutter as I found that most of my customers now, have brush cutters under 35cc.
Going smaller however created another problem, where to put the anti-fouling blades? This was a part that I did not want to remove, as it is what prevents long stringy grass from wrapping around the gear head. So the only place for it was as shown below. Enter a new shape rubber impact hub form a new stronger and more expensive mould.
The problem with this design, is the area that takes the hardest hit from the flail-blade has the least amount of travel and even this very hard rubber was blowing itself apart from the shock of the impact. Unfortunately I do not have a close up lens to show you how the rubber is tearing itself apart, but if you look closely you can see the spiral tares in the rubber.
This rubber is more than capable of withstanding very high loads without any loss of memory for its original shape and theoretically can easily withstand the load forced placed on it from the flail blade. However what does the damage is the speed of the impact, as the velocity of the shock wave increases the rubber is no longer able to give way quickly enough and that energy blows the rubber apart.
Putting it simply, the higher the velocity, the more the rubber starts to behave as a solid, keep increasing the velocity and it will behave as a piece of ice. This might mean that this blade may not be suitable for very high powered brush cutters that can be pushed really hard without losing speed. The steel can handle the punishment, but maybe the rubber cannot, only time will tell me this as I get feedback from the commercial customers.
This model has only very slight changes of the location and angle of the anti-fouling blade and the removal of rubber where the velocity of the impacting blade is the highest. I had hoped that the rubber would take a good portion of the impact shock and the anti-fouling blades would take the rest of the hit that the rubber could not handle.
Below is the red rubber sample B, which still showed signs for disintegrating in a very short time, although it is not visible in this photo. unfortunately as I found out later, adding colouring to the rubber makes it more susceptible to fracturing under high speed impacts even though it is the same hardness as the yellow sample.
Below is one of the original yellow samples that was too thick to fit in-between the top and bottom hubs. It was sanded down to the right thickness and then cut the the right shape.
This uncoloured yellow rubber is able to absorb the impact shocks, but even as hard as this rubber is, it was compressed 9mm and there was still enough energy left in the flail-blades to shear through the anti-fouling blades as can be seen below.
So the question here is, how do I maintain the success of prototype 17.2, but make it smaller and lighter and that is to move the anti-fouling blade away from the impact area as in the Model-17.2which can see below. Unfortunately to keep the weight and hub diameter down, the anti-fouling blades are so small that I expected the be near useless.
Below you can see that I am continually shaving away the hubs to reduce weight and test that the strength is still there. I had also hoped to keep the flail-blade unchanged for longterm ease of parts supply, unfortunately the only way to protect the rubber from high point impact zones and failure of the rubber was to redesign the back of the flail blade.
Another problem that I encountered with this design, using the Model-16 flail-blade, was the amount of spring back from an impact. This meant that the flail-blade would bounce back and forth who knows how many times as you cannot see it, you can only feel the extra vibration it causes. This bouncing back and forth would only stop as a result of either slowing or speeding up the blade until it settles back into its normal cutting position. Keep the brush cutter at the same speed and the flail-blade would continue bouncing back and forth, causing a lot of vibration and strange sound.
Anther added cost, was to get another high pressure mould made, this time just a round disc, which allows me to freely adjust the outer profile until it is able to withstand the impacts and at the same time cause minimal bounce of the flail-blades.
Below is the model-17.5 fitted to the brush cutter and if you look carefully you can see how small the anti-fouling blades are. I had thought that these very small anti-fouling blade would be near useless, but infact they work better than the much larger multi anti-fouling blades as found on the model-16 blade. An unexpected win, after so many failures.
After a couple of tanks of very hard use, the bolts that clamp the gear head to the shaft had stripped the aluminium thread allowing the gear head to work its way off far enough to disengage from the drive shaft.
Here you can see the angle of the gear head, another 10mm and the whole gearhead, guard and blade would have come off.
This is what I was testing this blade on, cutting up an old fallen gum tree where the wood is dry and very hard. But this is the most extreme conditions that I think anyone would ever put a brush cutter through.
Below are the two heavy duty Stihl gear heads I have gone through in the precess of extreme testing the Model-17 prototypes. With one, all the threads in the aluminium body were stripped out and the other the gears were worn away enough for them to no longer mesh. The problem was not the hardness of the gears, but that hypoid gears should not be lubricated with grease when the meshing speed exceeds 200ft/min. This results in the grease being compacted against the casing wall and not enough on the gears to lubricate them.
I like pulling them apart to look for the problems and weak points so that the gear head I design in the future will be able to handle this sort of punishment. The seals need to improved so that a high pressure hypoid gear oil can be used as in the diff of a car, instead of grease.
So before you Armchair Generals out there, who have to point out that this is not what a brush cutter is supposed to be used for, or as one very intelligent General put it, USE A CHAIN SAW MATE! (actually he said dickhead, which I found very offensive) It is sad, that the only contribution some people can make, to making the world a better place, is to run down someone else that is at least trying to make a difference.
If you are not happy with the contribution I am trying to make, please don’t email me about this, just leave this site and go and vent your frustration somewhere else.
And yes I do get emails like this and worse, which is why I deselected the comments section on the pages of my web site.
As far as I am concerned, I am estatic that the brush cutter breaks before the blade, but that is beyond the scope of a (smarter then the average bear) General who only looks at the pictures and does not read or take in what has been written on these pages.
Below is the next version, the hubs are the same but the flail-blades rear edge and the outer profile of the rubber has been changed to see if I can reduce the high speed impact load to the point that the rubber will last a long time.
Below is a another new gearbox attached to the brush cutter to continue testing the the revised model.
Below is the blade after about 15 hours of really hard clearing of rainforest undergrowth, ranging from long stringy grass to sapling regrowth and fallen dry and hard branches up to 200mm. Even though the rubber has abrasion marks on the side, which was from silver paint so that I could see how the rubber was compressing. Close inspection showed that there is no signs of failure of the rubber.
Unfortunately, there was still some acceleration induce vibration, caused from the flail blades swing back and forth, that was not a problem with earlier heavier version. After a lot of observation to try and determine the cause, I found out that the weight ration between the hub and flail-blade is critical and so I determined that I needed to add extra weight back onto the hubs as I did not want to remove any more weight from the flail-blades. I am guessing that it was this same weight ratio issue that caused vibration, with the two bladed Model-15 blade.
Below are some pictures of the final Model-17 blade, which will be released in July 2017. It will sell initially alongside the Model-16 blade, until the Model-16 blade sells out. Unfortunately, due to the extra parts in this new model, it will have to sell for at least $60.00 more than the Model-16 blade.
For the last couple of months now, I go out early every morning to burn up a tank of fuel putting this blade through it paces and every time I use it, I am amazed how well it cuts and mulches up everything that gets in its way. Even though this blade is smaller in diameter and lighter especially the flail-blades compared to the Model-16 blade, as you can see below. It runs that little bit smoother, cuts that little bit better and clears grass that could grind the blade to a holt just that much better. In fact, with the exception of the price, everything about this blade is better than the model before it.
Perhaps I should add here, that all the testing has been done with a modified long shaft brush cutter, with a Stihl gearhead and guard and powered with a 35cc Honda 4 stroke engine. This brush cutter is so good, that I couldn’t bring myself to waste money on any other brand of brush cutter to further test this blade. I am not saying that these other brands are no good, just that they have all focused all of there development on bicycle hand models, to the detriment of loop handle models, which I think is a big mistake as none sell higher powered loop handle brush cutters.
Below you can see the final shape of the rubber impact stop.
Below is the Model-17.7 fitted and ready for testing, everything on this blade is new, with the exception of the bolt, bush and nut. The same second generation, bush-bolt assembly has been used on the model-17.5, 17.6 & 17.7 to test the durability of the revised bush bolt assembly.
The most expensive addition to this Model-17 blade, is the addition of the nut guard, with the cost price for this part alone being $19.00, but it is worth every penny.
The first nut guard on the left, cost $5 to machine from a 35mm solid bar, of the same steel as the high tensile bolts. It was cheap and light, but the problem with it was that it allowed the blade to slip and the dirt would easily compact in around the lock nut and was very difficult to clear out to undo the lock nut. The thin edge also wore away easily on gravelly ground.
The second nut guard on the right, is CNC machined from a 50mm solid bar made from the same steel as the bush and heat treated to the same hardness as the bush for long life, which is why it cost four times as much. It locks the blade up so that it does not slip, it is easier to clean out to undo the locknut and the increase slope allows the blade to easily slide over branches laying on the ground without snagging as you move the brush cutter from side to side.
This twenty odd dollar cost, would for many, be the price they would have to pay anyway. As most lower powered brush cutters now, no longer come with a nut guard, spring washer and lock nut to fit a metal blade as standard equipment with the brush cutter.
With the exception of the lock nut, which may still need to be purchased, the nut guard is part of this new blade and the rubber impact stop also acts as the spring washer meaning one is no longer required.
It is amazing how quickly you forget about a problem once it is solved and you have moved onto new problems. With all the testing I have been doing, I was beginning to think that I could not longer keep this up as my hands were permanently tingling from all the vibration they have been subjected to. Yet yesterday, my partner Linda asked me how my hands were coping and I suddenly realised that they were fine, so I guess the latest model anti-vibration gloves really do make a difference, even though they don’t feel like they are making a difference.
I recently spent another evening with a good friend, who again harped on that I secretly have no desire to succeed in business and have endured this from him every time I mention an upgrade. Why for gods sake do I keep wasting my time and money continually improving the blade, when it is already 50% better than anything else on the market and probably 90% as good as it could ever get. Leave it alone and move onto another product.
And of cause in a lot of ways what he says is true, unfortunately the world is no longer a simple place and the quick answer to this is liability. If I knowingly become aware of a flaw in the design, sweep it under the carpet and continue selling it regardless it will eventually come back and bite me as many car companies have found out the hard way. Personally I do not want to loose my house and or spend the best part of my later years fighting law suits.
So for my thinking it is good business, because if I want to move the selling of my products over to the retailers, they have to know that the product they are selling is safe and will not come back to bite them.
And that if I want to continue living my current lifestyle on top of an unheard of plateau mountain that is green like Ireland and that most Australian’s can only dream of and or to develop a business that does not have the hassles of employing staff than it makes perfect business sense.
I would also like to mention that the current Model-16 blade is perfectly safe and there has never been a catastrophic failure where the blade has blown apart. However a very small number of people with high powered bicycle handle brush cutters that have used the standard brush cutter supplied 3 or 4 bladed knife blade for some time and have developed the bad habit of throwing the brush cutter into the job (like in my video above), to bash their way through a branch. It is this type of bad cutting habit that has resulted in four failures (that I know of to date) of the bottom hub, but not the complete blade.
Why spend so much time and money reducing size and weight?
After much feedbacks about the size and weight of the current model-16 blade, I decided to do a google search of the location of customers for the last year of sales and found that by the start of 2017, almost 50% of sales were now going to residential properties especially in the United Stated.
Up until then, I have been focusing all my energy on making this blade heavier and stronger to withstand the punishment dished out by commercial clearers. Whereas in fact they now only represent an extremely small percentage of the market.
I was also surprised to find that the number of woman using this blade has increase and may be, at a guess as high as 5%, based on email feedback and questions asked.
However this exercise of bigger and heavier has not been a total wast of time, the result is now a brush cutter blade, that for the back yard user with a 25cc Bruch cutter, is safe and indestructible in the backyard environment.
As I could see from the aerial photos, not everyone has a manicured back yards and for a lot of people (especially in the higher rainfall areas) maintaining a back yard jungle can be hard on equipment and especially time.
This new model blade will be designed to withstand the punishment from a commercial clearer with a 50cc high performance commercial brush cutter, but can also be easily driven by a 25cc consumer brush cutter.
It is especially suited to the slower revving Honda 4 stroke engine and eventually, the even slower revving electric brush cutter as more of them come onto the market with the ability to fit a metal blade. This blade does not need high revs to clear, even the thickest back yard jungle.
I would like to make the point here, that even though this blade is safe in itself, using any metal blade in a built up residential area comes with responsibilities on the part of the operator to use it safely, especially with respect to other peoples and neighbouring properties.
These responsibilities also include being aware of what direction debris is being thrown and planning your cutting to control where the debris goes. Plus the regular inspections of the blade and brush cutter before each use and when refuelling to ensure nothing is coming loose as cutting heavier material results in more vibration to the brush cutter than you would get form a nylon head.
The Model-17 Blade is available in four options, click photo below for more option and purchase details.
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