snapped cutter wheel shaft

[stavenstumper]

While grinding a rather small stump this weekend with a 98 Rayco RG20HD, the cutter wheel shaft snapped. Has anyone had this happen? What likely could have caused this?

 

[Stumper]

A flaw in the metal-either a void or inclusion or , more likely, a problem with the heat treating. A 98 probably has a lot of hours on it but Rayco probably would like to know about it. They may provide a free replacement-it not the cost isn't too high-I chewed up the shaft with a spun bearing on my RG12 a few years ago and purchased a new one I've forgotten the exact cost but it didn't kill me.

 

[Lumberjack]

We have a new cutter wheel, axle and bearings coming for the RG85. Its not worn out but its showing wear from the chips on the wheel. Wanna have the spare to swap it out right then and there. We do have 1700 hours on it though....

 

[Ekka]

Hey stavenstumper

I've seen it before. How many hours on it?

The problem can be accentuated with these grinders when they jump over the back of the stump or the operator thinks it's doing a better job when grinding the back of the stump. The machine stops a lot. Not good, also rocks and roots that get stuck in the wheel ... not good.

The constant pounding, more so when you don't change the teeth often enough, crystalize the metal ... usually breaking at a weeker point, a shoulder, groove, bearing surface etc. These shafts are only small in dia for what they're doing.

Metal fatigue, it happens.

 

[Proj Eng]

Take a picture of the fracture area and we'll see if we can correctly identify the type. But, even before I see it I would guess fatigue failure. And I'll bet it started with a crack in the shaft surface.

 

[stavenstumper]

Thanks for all the replies. I think you hit it on the head Ekka. I am guilty of going to the backside of the stump with the back of the wheel. I did not know that would do any harm. I guess I was wrong. BTW, the machine has about 440 hours. I will go see my local Rayco Distr this afternoon. I do have to say about Rayco, they are very helpful. I lost my manual they emailed my the entire manual in a PDF file. The local Distr gave me the name and number of a guy in the service dept in Ohio. I have called him on occasion and he has answered my questions. He knows his stuff...Hope to have repaired by the weekend. Thanks again...

 

[Lumberjack]

Grinding with the back of the wheel would be grossly ineffiecent IMO. Never tested it. Using 3-6 on the wheel (clock face) is the most logical. Pulls the fibers apart with greater ease.

 

[Ekka]

I am guilty of going to the backside of the stump with the back of the wheel. I did not know that would do any harm. I guess I was wrong.

I'll try to explain why. When you use a chainsaw conventionally, you know, cutting with the bottom of the bar ... it pulls the saw in to the wood and you get leverage off those bumper spikes. And when you cut with the top of the bar it tries to push the saw away from the cut, back at you, and you have little leverage ... just your arms getting a good work out.

So, this is called a pulling chain or pushing chain, pulling cut or a pushing cut.

Now think of your stump grinder similarly. When you are grinding the front of the stump using the 3 o'clock to 6 o'clock area of the cutter wheel you have a pushing feeling. You got to heave on that handle and keep the pressure on the stump ... this is the conventional way of grinding.

Now think when your grinding the back of the stump using the 6 o'clock to 9 o'clock area of the cutter wheel you have a pulling feeling. The chassis of the machine becomes like those bumper spikes and you get leverage onto that stump. So you can put a heck of a lot more force on it. But sometimes if the stump is up high you'll grab and dive deep into it jamming the wheel. Also the way the wood chip comes off the cutter and is dealt with by the machine is different and the likelihood of having bits getting stuck is higher because they are getting throw up in that little gap between the top of the wheel and the housing. Rocks and roots that may have been throw out the back of the machine are now getting chopped up and pounded in that gap.

So, like any piece of steel that you bend over and over again till it fails these minute bends at 2000 rpm exacerbated by vibration and a 50lb cutter wheel all add to the fatigue factor.

 

[Al Smith]

If I am following this correctly,it's like "climb milling",with a milling machine.Moves a lot of material,but also puts a lot of stress on the cutting mechanism.

 

[juststumps]

i'm with lumberjack on the 3-6 thing...what i don't understand......how and why, would you cut a stump backwards??? do people drive over the stump,,, start cutting on the far side,,, then back their way out????why???? less mess, maybe????i i'm at a loss!!!!

 

[Ekka]

Al Smith, it's not quite like climb milling because with climb milling the cutter is moving in the same direction as the feed. But grinding a stump you sweep across not plunge in and go forward or back ... I hope you get it.

Juststumps, yeah, once you can get over the stump that's what people do, with the hand type machines like Dosko 20hp, Rg20, Vermeer sc13 etc, they grind the back!!

You'd have to own one of these machines to find out but it's a bad habit. If the brake is worn or the surface slippery many times the machine will drag forward into the stump ... but if you get over the stump to the back you feel "safer" ... but it's not the case as per my previous post. Best if you don't do it but I bet it happens a lot.

 

[juststumps]

ekka, never used one of the smaller machines... from what i hear,, it's about 10 times harder than using my old front tine roto tiller.....never again...if i want a arm workout,,,i'll go to the gym...

 

[Ekka]

You're spot on there. I use mine for difficult access jobs but even then I'll try to take gates and fences down to get the auto machine in.