Possible to sharpen push lawn mower blades with angle grinder?

[Muse]

I never knew anything about hand held angle grinders until a couple weeks ago. Had difficulties getting one from my local tool lending library so looked them up at Harbor Freight, figuring they'd be cheap there. I've gotten a lot of tools, most adequate over the years but never any power tools. The reviews on their cheapie for $10 with coupon made me think it was well worth getting (even several at that price so you don't have to change blades).

Well, investigating these things I saw a lot of mention of sharpening lawn mower blades with them, that they do a great job of that. Would that just be for power mowers? I know, most people when they talk about lawn mowers are talking about power mowers. My push mower I've tried to sharpen a few times with a small stone but I don't think it helped a lot. The mower's about 17 years old and I'm having to work a lot harder to mow the lawn, going over spots several times.

Wouldn't it be tough to get the blades even with a power tool like an angle grinder? Are there tricks to do this properly?

 

[Pick2]

The first step is to Remove the Blade From the Mower.
You could use an angle grinder , but I've been using power tools my whole life , and I wouldn't attempt it.
Use a bench grinder with a tool rest on it so you can keep the right angle on the blade. Take equal amounts off each end of the blade or you will unbalance the blade.
You might be better off letting a mower shop sharpen and balance it for you.

I never knew anything about hand held angle grinders ... I've gotten a lot of tools, most adequate over the years but never any power tools.

if you decide to angle grind it while still mounted on the mower , please post Pics of any cuts, stitches or missing fingers
Seriously ,Be careful !

 

[pcgeek11]

He is talking about a Push Mower:

 

[Pick2]

If he is talking about a "Reel Mower" , you can't sharpen them by hand.
If it's 17 years old ... just buy a new one ... they start at $60 - $80 dollars

 

[john3850]

I would not use a grinder do the twist and lack of room to work around.
Just use a file on both sides of each blade keep the file clean and only push one direction.
If you cant file good buy a new mower.

 

[Pick2]

Quoted from second post:
http://www.doityourself.com/forum/e...7-sharpening-old-timey-push-mower-blades.html

"In order to cut correctly, each blade has to be sharpened exactly equal to all the others. The bed knife must also be sharpened. Then the reels blades must equally and evenly come into contact with the bed knife edge.

Basically, sharpened and adjusted correctly, the reels 5 or 7 blades, when coming into contact with the bed knife, creates a shearing effect much like a scissors.

Any attempt to sharpen the reels blades or the bed knife without the correct machinery, will ruin the entire assembly."

 

[john3850]

I never could sharpen any scissors so I guess it is time for a new mower.

 

[Greenman]

Go ahead and sharpen it, you have nothing to lose. If it doesn't work you need a new mower, if you don't try it you need a new mower.

 

[Muse]

Go ahead and sharpen it, you have nothing to lose. If it doesn't work you need a new mower, if you don't try it you need a new mower.

Yup. I have the manual, don't remember seeing instructions on sharpening, though. I'll have another look.

I'm pretty seasoned in sharpening concepts, have sharpened my tools for many decades. This would be the most complex sharpening project I've tackled, though.

I actually made my own drill bit sharpening jig many years ago, still have it. It's not perfect but does a pretty good job.

My bench grinder is a home-made affair made from scrap wood and an old discarded laundry dryer motor (that I bought from an odds and ends shop for $5 many years ago). I made a tool rest for it, just some metal screwed in place.

What I've done in the past is use a very fine and small sharpening stone in trying to sharpen the blades of this push mower, which is a Craftsman. I have never thought of or attempted to deal with sharpening the other steel that shears against the rotating blade assembly. I'll see what I can do. Just cleaning things up should help to begin with. Yeah, an angle grinder would seem to be inappropriate for this as well as general dentistry!

 

[mindless1]

In recent years youtube has started to catch on with the DIY maintenance crowd. Even dentistry.

https://www.youtube.com/results?search_query=sharpening+reel+mower

 

[boomerang]

In recent years youtube has started to catch on with the DIY maintenance crowd. Even dentistry.

https://www.youtube.com/results?search_query=sharpening+reel+mower

As someone who was a lawnmower mechanic many moons ago, I heartily approve of the process in that link. The only thing I would do differently is to apply the lapping compound as the reel was turning. It's easier to apply it that way than was shown in the video. Grass is typically thicker than paper so the ideal situation is to not have the reel and the bed knife touching at all when the job is completed. It can be difficult to achieve that type of tolerance though. Second best is to have as minimal contact between the two as is possible.

 

[Muse]

As someone who was a lawnmower mechanic many moons ago, I heartily approve of the process in that link. The only thing I would do differently is to apply the lapping compound as the reel was turning. It's easier to apply it that way than was shown in the video. Grass is typically thicker than paper so the ideal situation is to not have the reel and the bed knife touching at all when the job is completed. It can be difficult to achieve that type of tolerance though. Second best is to have as minimal contact between the two as is possible.

Which video is that that you really like. The link is to a collection of videos about sharpening lawn mowers. Is it the first one, 7:18?

Edit: I guess it was the 7:18 one you watched and liked. He said it was a Scott's reel mower. Mine's a Craftsman. Maybe they're sufficiently alike the technique would work. I don't have the sharpening kit he uses though. Maybe I could get by with a power drill and polishing compound, though kind of like he did.

 

[stormkroe]

I think good blades are 5160 steel, I've used the ol' grinder on quite a few in my days. If you're new to angle grinding, DON'T LEARN ON THIS. Also, don't take the metal past light-wheat in color or you'll lose rockwell.

 

[Muse]

I think good blades are 5160 steel, I've used the ol' grinder on quite a few in my days. If you're new to angle grinding, DON'T LEARN ON THIS. Also, don't take the metal past light-wheat in color or you'll lose rockwell.

Yeah, TBH I've had about 10 minutes experience using an angle grinder, the one from my tool lending library, a Bosch. I used it to grind off exposed nail tips that came through the rough-shod job on my garage's roof lately done. I bought 4 ten buck models from Harbor Freight. Repacked the grease in them but haven't used them yet.

I understand the light-wheat idea, I think you're talking about not drawing the temper, something I understand pretty well, having messed with steel for many years. I've retempered tool steel. Playing with steel is really fun. I've case hardened ordinary steel. That's the way they used to harden steel centuries ago.

Using the methods shown in the videos will not generate any significant heat such as would threaten the temper of the blades. Using an angle grinder might, though. It's kind of like sharpening something on a bench grinder, you have to be careful not to draw the temper of tool steel (high carbon steel). I understand high carbon tool steel in this regard, but there are a lot of other alloys out there. Those I don't know much about.

 

[boomerang]

I think good blades are 5160 steel, I've used the ol' grinder on quite a few in my days. If you're new to angle grinding, DON'T LEARN ON THIS. Also, don't take the metal past light-wheat in color or you'll lose rockwell.

I was a Die Maker for thirty years and had way more experience than I even wanted in grinding metal into complex shapes by hand. There is no way, by hand, with an angle grinder, to sharpen a reel mower with anything even remotely resembling satisfactory results.

Let's start with the reel. Let's pretend there is only one blade. One blade shaped in a helix that must create a cutting action against a bed knife that must be sharpened perfectly straight and true in two planes using mechanical equipment. Mechanical equipment because achieving the accuracy by hand over the length of it is pretty much impossible. If you can get a sharp edge on that one reel across it's entire length that will interact with the bed knife to cut grass across the entire length you are a person that could truly rule the world. Now do that to the remaining blades in that reel and you are worthy of ruling the universe. You are a super-human.

We sharpened reels by removing them and mounting them in a grinder that spun the reel against a grinding wheel while traversing back and forth. The process had to be approached with skill and patience. Heat is the enemy and the reel should have no taper from end to end. You don't want a helical cone when done. Once the cutting edge is in place across the length and circumference, the blade must be backed off. This creates a secondary angle to provide relief and define the cutting angle. A carbide finger is installed very close to the grinding wheel to act as a rest and is adjusted to provide the angle desired for the relief. Then each blade must in turn be run across that finger until the desired width of the cutting edge remains while not introducing undue heat.

The bed knives we typically replaced and put them in another piece of equipment to grind them true and flat in two planes. A cutting edge is derived from those two planes.

Because achieving perfection in those processes is too time consuming, the final part of the process is to lap these surfaces to knock down the high spots.

Because end users don't have the grinding equipment needed to sharpen a reel their only recourse is the lapping process.

 

[boomerang]

Which video is that that you really like. The link is to a collection of videos about sharpening lawn mowers. Is it the first one, 7:18?

Edit: I guess it was the 7:18 one you watched and liked. He said it was a Scott's reel mower. Mine's a Craftsman. Maybe they're sufficiently alike the technique would work. I don't have the sharpening kit he uses though. Maybe I could get by with a power drill and polishing compound, though kind of like he did.

Correct on the video but polishing compound isn't going to be course enough. You aren't looking to shine up the cutting edges, you need a compound course enough to alter them.

 

[J.Wilkins]

I never knew anything about hand held angle grinders until a couple weeks ago. Had difficulties getting one from my local tool lending library so looked them up at Harbor Freight, figuring they'd be cheap there. I've gotten a lot of tools, most adequate over the years but never any power tools. The reviews on their cheapie for $10 with coupon made me think it was well worth getting (even several at that price so you don't have to change blades).

Well, investigating these things I saw a lot of mention of sharpening lawn mower blades with them, that they do a great job of that. Would that just be for power mowers? I know, most people when they talk about lawn mowers are talking about power mowers. My push mower I've tried to sharpen a few times with a small stone but I don't think it helped a lot. The mower's about 17 years old and I'm having to work a lot harder to mow the lawn, going over spots several times.

Wouldn't it be tough to get the blades even with a power tool like an angle grinder? Are there tricks to do this properly?

Keep using the stone, if it's not enough use a lower grit emery cloth. You don't really need to take off that much. The bed knife you can sharpen on your bench grinder as long as you can keep it even, finish off with emery cloth or sharpening stone.

 

[Muse]

Correct on the video but polishing compound isn't going to be course enough. You aren't looking to shine up the cutting edges, you need a compound course enough to alter them.

Thanks. I figure to go to a big hardware store tomorrow and get some compound. I'll look to get a coarse one. The only stuff I have like a polishing compound is some solid sticks I picked up from Harbor Freight IIRC, which are used to apply to spinning buffing wheels for ultimately shinning steel, at least that's what I tried to use them for. These days I shine up my stainless steel by using wet dry sandpaper, starting with 180 or even 150 grit and working all the way to to 1500 grit for a practically mirror finish. This is mainly my stovetop coffee maker, which I have given that treatment a few times.