Blade snapped off, bounced off some nearby object, went right through a leather boot and buried itself into the side of the operator’s right foot. After four years, this is the first time I have had feedback of a complete blade breaking away at the pivot hole and in this case causing a serious injury that required surgery to fix some shattered foot bones and stitching up.
There were multiple causes that lead to this failure;
- The operator did not take care to keep the blade teeth sharp, so instead of cutting through the bush, the operator was bashing his way through it thereby putting much more stress on the blade and brush cutter.
- The operator had a very powerful commercial brush cutter and used this power to lean harder into the job. This caused the Anti-Fouling-Blade stops to all fail and fly away.
- The operator continued on in the same manner, except now the Flail-Blade was smashing against the lock nut but before stopping against the nut, the blade had to ride up the tapered locking washer severely twisting the blade in the process.
- The design that resulted in a very small, high impact point between the back edge of the Anti-Fouling-Blade and the Flail –Blade, this combined with a sharp edge at the back of the Flail-Blades created a seed point for a crack to start.
- Lack of regular inspection by the operator, as these cracks have been developing slowly over a period of time and should have been picked up before one of these blades failed. As tough as these blades are, they are not indestructible.
Below you can see that both remaining Flail-Blades had serious cracks leading from the sharp internal corner and going half way through the blade.
You can see by the stain marks that the crack had been present for some time.
Redesign the Flail-Blade, to remove the sharp edge that can seed a crack, add an Anti-Fouling Blade and relocate the other to reduce the impact loads resulting in a blade that can take much more punishment. The failing of a blade, causing injury is something that cannot be tolerated, because if it can happen once it could happen again and possible resulting in even more serious injury.
By doubling the thickness, adding an Anti-Fouling-Blade, relocating the other, it has been possible to move the fore and aft impact points further away from the pivot point, thus reducing the impact loads on the Flail-Blade, the Anti-Fouling-Blade and the pivot bush.
Below you can see the fore and aft impact points and its distance from the pivot point.
Below you can see the new model Brush-Cutter-Blade, with the extra double thickness Anti-Fouling impact stops. You can also see the impact distance from the pivot point and that the impact point is in the centre of the Anti-Fouling-Blades making id far less likely for the Flail-Blade to shear its way through the Anti-Fouling-Blades. You can also see that there is much more metal and no sharp corners near the pivot end to seed a crack. I have now tested this design for about 150 hours of very hard use and at this point I have seen no signs of failure of either the impact stops or the Flail-Blades.
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