Sharpening large mower blades

[Bill Bob]

Is there a tool that perhaps will chuck into a hand drill to sharpen the blades on my 72 inch mower?  The 3 blades are 3/8 to 1/4 inch thick.  The factory angle on the cutting edge looks to be about 30 or 40 deg.  Is that angle critical? And what about grinding on the flat side?  I have been using a hand held grinder with blades mounted in a vice.
Thanks,
Bill

[JosephP]

Check AM Leonard. I get their catalogs...see a lot of mower sharpening stuff, but don't pay much attention. I take mine off and sharpen with file. Used to use grinder, but file does a great job...

[Admiral]

I'd suggest you invest in a good quality coarse 12" person mill file.  I used to grind my mower blades (52" deck) but found that you take off too much steel, have to rebalance them, and they get dull quickly anyway.  Since I switched to a file, less metal is removed, it really does not take long (15 minutes) and you don't have to replace the blades as often.  If you read the manual (mine is John Deere), keen-sharp is not recommended and the angle is not all that important as close enough is good enough.

That being said, I guess one could make a jig out of wood and use a Dremel with a grinding stone bit, I've done that in the past.

http://www.homedepot.com/p/Dremel-1-8-in.../100531886

[fixtureman]

I take the blades off and use my belt sander with a 50 grit belt

[daddo]

At some time you're going to get a lot of nicks in that blade and you're going to have to take the surface back to the inset of those nicks to get rid of them and at the same time, keep the proper angle, and that means removing a lot of material.
A sander with a 36-40 grit works ok. I use the 72" belt grinder which will remove the material very quickly. Like mentioned, a regular belt sander works to a lesser degree but is a good way to do it.
First sand the edge flat and remove the nicks, then start sanding/grinding the angle until it is sharp, but not too sharp as to create an easy to nick edge. The edge should not be razor sharp- a very slight blunt edge won't nick as easily.

[Bill Bob]

Sounds like a good idea,  should I stay away from the flat side?
Bill

[Herb G]

You only sharpen the bevel. If the flat side has huge chunks out of it, you can get away with filing them flat. Otherwise, replace the blade.

[Kansas City Fireslayer]

I have went the past 4-5 years with only using a double cut or mill file when sharpening the three blades underneath my 48" mower.  Granted, I'm not hitting rock in my residential yard so it's very rare that I get any significant damage.  If you touch them up once or twice a year, a file really doesn't take long to establish.  I admit I have raised the cutting edge angle (secondary if you will) a touch over the years.  I will also add a back bevel on the underside if I really need to get to fresh steel quicker.  The back bevel is as mild as I can apply and room will allow.  You don't need to remove much metal at all.  The only part that cuts is the very tip.

Guys I work with have brought in their mower blades and I've watched them grind repeatedly with a 4" angle grinder.  Ironically, I could of had the same result, or better, with a file in a small fraction of the time and steel.  I guess the blade gets sharper with each continued swipe with an angle grinder....for some.  You don't need scary sharp to cut grass cleanly....

[tomsteve]

PLEASE tell us youre balancing the blades,too.

[Stwood_]

Remove blade and use a 4" angle grinder. We have a lot of rocks here.
When done, put a long whatever size length bolt in the vise, and hang the blade  on it. You can balance it real easy by taking some off the heavier side.