Right way to sharpen rotary cutter blades

[Rio_Grande]

When I bought my 72 inch rotary cutter the salesman told me I couldn't sharpen the blades with a grinder because they had to be harder than regular blades. Said I had to have them pounded back into shape. I don't know the right answer but we have sharpened all kinds of blades with grinders and never had an issue. One side of my blades is trashed due to an unseen manhole cover in the middle of the woods 3 days after I bought it. So I have run in the other direction ever since. I dressed the edge a few times with a grinder, but they never got dull enough to really require any more that a few passes on the edge. I did a larger than normal job recently thinning hardwood trees, lots of 5 inch oaks and walnut trees and by the bed of the week I really noticed a difference in the way they cut. Sure enough when I inspected my machine today before starting I have about a 1/4 inch rolled edge on the last 4 or so inches of the blades. I am not even sure where I would get them pounded back out at, but I have a big grinder! The other side is jacked up, looks serrated. New ones were quoted to me for 300 a set. So if I can clean these up I would be happier. What say the experts?

 

[4570Man]

I'd grind them, but make sure to grind them equal. If you are trying to take out 5 inch trees a forestry flail mower would be better suited.

 

[Tractor Seabee]

I'd grind them, but make sure to grind them equal. If you are trying to take out 5 inch trees a forestry flail mower would be better suited.

Don't forget to weigh each one for balancing. I 1/2 OZ difference is the spec per one manufacturer (Land Pride). The heavier the grinding the more they could start to get out of spec. LP says: "do not pound them our or heat them".

Ron

 

[the old grind]

I'd say hammer what you easily can (big anvil, big hammer, big gloves to hold at the best angle) and then clean 'em up enough to take to a welding shop if available. (well under $100 around here ...)

Welding heat might reduce some of the stresses from the original damage and the initial pounding back. Call a shop and ask them. I'd be surprised if they didn't say "bring 'em & we'll have a look". Call around if you have several to approach.

Dip regularly into a water bucket to keep heat down as you grind, and be careful what you ask for in regards to 'toughness' for welding-up cutting edges. Some nickel steels are hard enough (>55RC) to eat most gen purpose grinding wheels, even 7" ones, and some guys will pile it on too thick. DAMHIKT

(got a good size mig to practice a few passes on an old lawnmower blade or two? ...)

I wouldn't sweat the angle you grind, just finish to equal weight. Steeper (blunter?) edge angles will resist bending over, and we're not usually after a finish mower's 'cleaner' cut when slashin' serious. tog

 

[boggen]

you do not need a razor blade sharp edge. instead the the cutting edge is more like a baseball bat. that swings around and busts weeds apart. ok not that dull like a baseball bat. but still attempting to get idea across more than anything of more of a duller blade.

you most likely will want to keep the "vibration" down. so balancing out the blades with each other. would be a good idea. un balanced blades = more HP to cut and more wear tear on everything.

==========
some folks use rotary cutters like finishing mowers. and may on purpose put a sharper edge on the blades. and be much like finishing mower blades but just larger blades. rotary cutters that have "under deck shields" that are circle in shape more likely work better for a finish mower setup.

rotary cutters, that have nothing under deck expect the blade itself. more likely geared for rough cutting pastures and like were look is not all that important but rather making sure you get through things faster and wanting to deal with less spots for crud to build up, when it comes time to clean the rotary cutter up and put it away.

to above... some rotary cutters from manufactures are setup differently. and blade recommendations and cut angles maybe different pending on the folks they are trying to market certain models to.

 

[Silvic]

Woods actually recommend the edge be a 1/16" edge, not razor sharp. I grind my Woods blades every so often. Have not yet added steel with welding but that time is coming.

 

[LD1]

I always grind mine.

But I gotta ask, what kind of cutter are you using to clear 5" hardwoods?

 

[lumberjack1986]

I clear 5" and double that trees with my rotary mower on my track loader (Bradco Extreme Duty Ground Shark). I sharpen the blades (3/4" AR400 steel) with a grinder... no issues. I use a Milwaukee M18 Fuel grinder... two batteries sharpens the 4 edges with power to spare.

 

[Mud Mechanik]

The OP must have a beast of a tractor to cut a weeks worth of 5 inch trees with a rotary cutter and it is still alive.

 

[Rio_Grande]

It can do 8+ on soft stuff. It's just an Rotary cutter on a CTL70 Gheil. Nothing fancy. We are starting a very dense 5 acre hilly site on wed, but it's almost all 4-6 in locusts. They are real soft at that age, nothing like cutting into them when they get hard. I just have to be sure to put the big ones off to the left side so the guard catches and stabilizes them. For the most part these won't require any lining up just cut forward tilt down and drag back!