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Im thinking I am needing to replace my rotary mower blades but wonder if they could be sharpen? Also I mow in the woods thus I run into limbs and stumps sometimes.

My problem stems from when I am in some thick grass the mower wants to clog up..but this tractor is a 5205 and should cut through it with no problem at 2000 rpms.

Any opinions
 

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Blades aren't that hard to sharpen. I've used a grinding wheel for years to sharpen mine. (You have to take them off the mower to do this.) If you keep up with sharpening them regularly, there are sharpening tools on Amazon that work well. Type "Smith's mower blade sharpener" into Amazon's search box.

But if you have a really rough edge and dents from hitting things, it may be best to replace them. Use a block of wood jammed in one blade to keep them all from turning when you are bolting or unbolting them. Note which way they go on before you take them off. I put an X on the side I can see from the bottom so that I'm sure to get them back on right. And make sure you look up the torque spec for your blades and use it to torque them back on. Under-torquing them or over-torquing them can make them come off and create a hazard.
 
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I raise the mower up with the 3 point hitch hydraulics then block it and sharpen the blades with a battery operated angle grinder and a metal grinding wheel. It is very quick and doing it this way avoids the need for removing the blades. It takes me longer to carefully block all four corners of the mower for safety than the actual blade sharpening. The problem I have is judging how much to sharpen them because the new blades are actually not sharp at all, but blunt.
 

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.... Under-torquing them or over-torquing them can make them come off and create a hazard.
Under-torquing I get, but over? We removed the blades to sharpen them all the time and when replacing them we NEVER torqued the bolts (I know now this was bad) but would tighten them with a cheater on a 3/4" drive socket. Our torque spec was "as tight as we could". Over torquing causing failure on this set up is something we never considered.
 

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If you take a fastner past it's maximum point of elasticity you weaken it and reduce it's clamping force.

A bolt is like a spring, as a kid did you ever stretch out the spring in a click pen. When you put the pen back together the spring was weaker.

In factory setting critical fasteners like those on a mower blade are often torque to yield. The DC tool tracks the force curve and when it flattens just before The force to turn it drops it stops. That level point just before yield is maximum clamp force. In the field most torque to yields are translated to a torque plus angle.
 

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I am thinking it would be difficult to over torque a blade bolt. Aren't they ususally grade 8?
 
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Good point Randy. You are upwards of 600 ft pounds. So maybe the Rock on the end of a 6 ft cheater, if the cheater didn't bend first.
 

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I am thinking it would be difficult to over torque a blade bolt. Aren't they ususally grade 8?
This is a valid point. But I suspect that most people who "field modify" specifications like blade bolt torque aren't doing it because they have the engineering knowledge of the components to make that decision. The other question to be considered: What "grade" are the metal threads that the bolt is fastened into? This metal would be under the same stress, and it would make sense in the design for it to be of comparable strength. But I've seen similar oversights in designs before, and I'm not aware of any markings on the female threads to help a guy like me make this call.
 

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This is a valid point. But I suspect that most people who "field modify" specifications like blade bolt torque aren't doing it because they have the engineering knowledge of the components to make that decision. The other question to be considered: What "grade" are the metal threads that the bolt is fastened into? This metal would be under the same stress, and it would make sense in the design for it to be of comparable strength. But I've seen similar oversights in designs before, and I'm not aware of any markings on the female threads to help a guy like me make this call.
All reasons to just torque to spec. I always put a torque wrench to all the important stuff. :thumbup1gif:
 
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Reminds me of the boom arm mower I used to run for the state. It was a brush hog style head with 2 blades - just like a regular brush hog but hydraulically driven.

600 ft lbs of torque for the blades which needed to be checked every day before running.
 

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Im thinking I am needing to replace my rotary mower blades but wonder if they could be sharpen? Also I mow in the woods thus I run into limbs and stumps sometimes.

Any opinions
I'd certainly try sharpening them first but to get that square corner at the tip of the blade again is going to take a lot of grinding. You might try grinding at a greater angle (35~40*?) than that preferred on a lawn mower blade of 30*.
Keep in mind the tip of the blade does most of the cutting. That will give the cutting edge more support under impact
Just food for thought. View attachment 214809
 

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If you take a fastner past it's maximum point of elasticity you weaken it and reduce it's clamping force.

A bolt is like a spring, as a kid did you ever stretch out the spring in a click pen. When you put the pen back together the spring was weaker.

In factory setting critical fasteners like those on a mower blade are often torque to yield. The DC tool tracks the force curve and when it flattens just before The force to turn it drops it stops. That level point just before yield is maximum clamp force. In the field most torque to yields are translated to a torque plus angle.
Sorry for the vague reply, as I re-read it was not clear, I'm a bit distracted with family health issues and I understand what you are saying.

As Randy said, with the size and grade of bolt, I thought it would be difficult to over-torque the blade bolts, IF I had the strength to over torque those bolts, I would be WAY impressed with myself!!!:lol:

I know beyond a shadow of a doubt that we didn't torque them to 600# (never had a wrench with the capacity to check them), but I also know we never lost a blade. :good2:
 

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Discussion Starter #13
i doubt i could torque mine to 600...since i have nothing that could go that high.

thanks for the replies folks. i may try to sharpen them first and go from there
 

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I had a friend that witnessed the event or aftermath of a blade breaking or somehow getting detached from a roadside mower and killing a car driver. My MX6 blade tip speed is 17416 ft per min or 198 mph. So blade attachment is very important.

I know many cutter manufacturers sell a "blade bolt kit". I am not sure if you should use bolts and nuts one time and toss them or if they have a certain number of uses or cycles.

At the dealership, the equipment set up mechanic had a torque wrench that maxed at 450. It was about 3 ft long IIRC. That is not long enough for an average man to reach that.

I think you can sharpen those blades but as stated, that last inch that does most of the work will take some time. The "sail" area on the back of those blades looks worn away, so they are not providing much lift for the grass cutting.

I try to keep 2 sets of blades for my cutter and mowers. It is easier to sharpen on the vise with my 7 in grinder vs under the mower with the 4 in grinder. I don't bang my head on the bottom of the cutter as much that way.

My Deere MX6 is fairly easy to change the blades on with the right tool. 3/4 in pull bar w/ ext and socket lowered thru the access hole in the deck to the nut. The extension keeps the pan from rotating while turning the nut. That is half the battle with this kind equipment. Almost as easy as changing blades on my Z925. It is harder to pick up the front of the ztr than pulling the 3 pth lever on the tractor.

Good luck.
 
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