Grading 425 Brush Mower blade bolt failure.

[Carpenter]

A friend of mine has a brush mower that I borrow once in awhile. I used it the other day and had the bolt that holds one of the blades break. I was lucky enough to find the spacer and washer in the grass and after extracting the broken bolt and replacing it with a new one the mower was back in business. The next day my friend went out to mow and the other bolt broke. I'm posting this as a heads-up to have some spare bolts, washers, spacers and a 5/8" easy-out on hand. This mower has been used hard for about 3 years and has hit many rocks so I don't think this is a premature bolt failure. The fatigue rate was amazingly close on the two bolts as the second one broke about 15 minutes (of use) after the first.

 

[BobRip]

That's quality, fail after three years within 15 minutes.
I have also used the easy out for removing the stub of a bolt. It is a lot easier than dropping the entire hub.

Usually I break the blades from hitting something like a stump. I think I have broken at least two. This was early in my use and now I have learned not to grind stumps with the brush mower. It does work OK on very very old stumps (they go to powder), but sometimes the stumps look old and still have a solid core.

Bob Rip

 

[BobRip]

Oh, I have also had the spacer when goes between the bolt and the blade fail. It's a good idea to keep an extra one or two. This only happened once.

Bob Rip

 

[MossRoad]

I've lost a blade twice on ours. Both times it was due to hidden rocks. What happens, I think, is that the bolt heads take a few hits on some rocks and that weakens them and they eventually break. Since the thing is spinning, both bolt heads probably hit the same item. I doubt it is fatigue. It probably hit something. If it happens again, I'd suggest changing, or at least inspecting, the head of the other bolt for dents, etc... it might just be worth it to change them both before taking a chance.

Remember, the brush hog is one of the most dangerous pieces of equipment. Spinning blades with lots of inertia in that heavy blade. The first time mine broke, the blade stayed directly under it. The second time it broke, it flew about 30 feet into the woods. That's why I will never operate the brush hog more than a few inches off the ground. I have been tempted to raise it up fully while it is running and bring it down on some heavy brush, but it would be too easy for the brush to tip the thing forward and then your neck and chest is at about the same height as those blades. Then factor in a stressed or cracked bolt and you're dead. YIKES!!! /forums/images/graemlins/shocked.gif

Better to knock the brush down with the PTO off first, then chop it up at ground level.