2.2.15 – Failure of Model-17 Flail-Blade

PROBLEM

Failure of Model-17 Flail-Blade

The Model-17 blade has been on the market for just over a year now (as of the 28th March 2018) and in that time I have not had any feedback of any failures of any parts of the blades. So to my knowledge this is the first failure of any part of the model-17 blade and I actually broke it.

Here you can see the broken flail-blade in the middle, compared to the other two. As you can see, they do not show much wear to the teeth because I look after them, but they would have done somewhere between 40 to 50 hours of very hard work. I go out on average 5 to 6 days a week and burn up a whole tank of petrol each time and I get on average 2 hours of run time for each tank of fuel.

When I received a new large run of the rubber impact stops, I found that with this run the rubber was almost clear and I was worried that it may not have been a good as the last run, so I have been giving this blade a real caning, clearing burnt saplings after the fire went through on our property.

After checking the break edge of the Flail-Blade, for any obvious chips or dents that may have seeded a crack and found none. I carefully inspected the top and bottom hubs and pivot bush for any signs of damage or failure and found none. I then inspected the rubber impact stop for any signs of failure and it was still in perfect condition considering the abuse it had taken. With hard use the flail-blades hits the rubber impact stop really, really hard and at very high speeds. But as you can see, the rubber has absorbed the shock without any issues.

So in this case, it was not the flail-blade coming to a very sudden stop, like it used to with older models blades, when it hit the metal Anti-Fouling blades that had no give. It was this, that had caused the failure of a couple of Flail-Blade in the very early models.

In the last month, I have been clearing burnt saplings, ranging in size from 10mm to 200mm in diameter, mulching up the smaller branches and cutting larger branches into about 2m lengths to easily carry to a nearby bon fire.

Below is a number of photos of what I have been clearing in the last month and at a very rough guess it would have to be somewhere between 3 to 4 Acres. Based on the memory of the size of my parents, 1/4 Acre section.

Below is an old dam that was completely overgrown with saplings.

The undergrowth was so thick here that you could not see any of the tree ferns, even after the fire, with the dead brown saplings totally blocking them out.

What is left of a large bon fire after clearing this area and behind it you can also see some of the uncut dead sapling that has yet to be cleared away.

This was another area that was thick with bush, that is now been cleared enough to mow for the first time.

Before the fire, I did not know that all the tree ferns were here and after the fire I thought they were all dead along with a thick layer of saplings. However the tree ferns were the first of all the plants to regrow after the fire and now that all the dead sapling have been cut down and cleared away, the grove of tree ferns look really nice.

Different view of the grove of tree ferns.

On the left, you can just see the dead saplings that I have not as yet cleared away. Although it is now possible to walk through it, it still blocks the view through it with a dead brown mess.

Below is three different views of a large area that has been cleared with this set of Flail-Blades fitted to the blade.

Although most of the saplings were less than 100mm in diameter, many ranged from 100 to 200mm in diameter.

The largest stump in this photo, would have been about 200mm in diameter.

This tree here was about 350mm in diameter and has been dead for a long time as there was lichen growing all over the upper part of the trunk that was not burnt.

CAUSE

I suspect that it was making the large ‘V’ notches in these larger trees, to get them to fall in the direction I wanted, that caused the blade to fracture and break off. To speed up cutting out the ‘V’ notch I was twisting and screwing the blade around to chip out as big a pieces as possible. I normally don’t cut down trees larger than 200mm with the brush cutter, but I was testing the rubber stop to the max, including cutting on the 12 to 3 o’clock area of the blade that caused a lot of shock to the blade.

Unlike me, you have nothing to prove and I do not recommend cutting down saplings over 200mm in diameter, especially when it is old, dead and very hard timber. I also recommend that when cutting out a ‘V’ notch, that you chip out the notch in small bits and not screw the blade around trying to grind out the notch as quickly as possible like I had been doing.

SO THE LESSON FROM THIS

As you can now see, as tough as this blade is, it is not indestructable and having a Flail-Blade flying loose is not recommended. I know exactly where the flail-blade let loose and when I clean up and burn this mess, I will try to find the missing bit, just to see how far it went.

Below are some of the fallen saplings, below that you can see the sapling that are laying on their side  and the side cuts to cut them into about 2m lengths read to carry to the next bon fire.

SOLUTION

To recommend that users do not twist the blades around, when cutting deep “V” notches to fell large saplings. Instead chip out the notch with lots of small straight cuts. This is almost as quick and save a lot of stress on the blade and brush cutter. I will do a video, to explain this in more detail in the near future.

I also recommend that you make it a habit to inspect the base of the flail-blades for any signs of cracking every time you refuel. If you think you might see a crack, sand the area with fine sand paper to clean the metal for a closer inspection as you can see below. Where this inspection found two flail-blades with cracks and these two are exactly in the same location as the first blade that broke.

If you should find that any signs of cracking, you should stop using the blade immediately and replace all three flail-blades with new ones. You should also contact me and let me know of this failure.

I have been asked by a customer, does this mean that there will then be a new model of blade in the near future?

YES, there will be a model-19 blade, that will include minor changes to the flail-blade to try and reduce the chance of a crake seeding in the first place in that same location. There will also be changes to the nut guard and nut and bolt.