Video Series - How to Sharpen Mower Blades

[enigma-2]

I use a Work Sharp flat grinder to grind my mower blades. It's slower rotation speed doesn't get the blades hot (grinding with a high speed grinder will form the edge, but you will find that the heat removes much of the temper, and the blade will dull faster after the sharping).

Work Sharp WS2000 Tool Sharpener - Amazon.com

I start by cleaning the blade with a wire brush, then dressing (light grind) the back side of the blade for a flat reference point. (The edge of the blade is referenced from the flat, back side).

I then remove the nick's from each edge so I have a fairly flat edge to reference from and try to remove the same amount from both sides so that the width of the blade is the same on both sides.

I grind at an approximate 30 deg. angle (whatever was on the blade to start with) I leave a flat edge on the blade of 1/16" (per blade spec.) Any sharper and it gets too thin and the edge will nick or chip faster.

After sharping, I use a wall-mounted balancer (the kind with ball bearings and magnets) to check and correct the balance. (Ebay, used).

Balancing is important as any imbalance will shorten the life of the lower spindle bearings or lower engine bearings. (And it makes for a smoother running mower or mower deck as well).

If I need to remove material to get a blade to balance, I extend the sharpened edge length-wise by 1/16" increments from one or the other side, until the blade is back in balance. (I try to maintain the same front-to-back width of the blade on both sides for dynamic balance. Extending the sharpened edge length-wise doesn't change the dynamic balance.)

The problem of using a nail is, they don't work with blades with a star-center hole, some blades have no center hole and even with a standard center hole, the nail never really gets positioned at the center of gravity of the blade properly.

I recommend that you do balance after every sharping and to use a small, cheap cone-type balancer. Should only cost $5 and more accurate than a simple nail as it will center the blades center hole better.

 

[motoman]

Please...bench grinders will not over heat if used properly. Clean wheel. Any wheel diameter . Grits of 46-80. Reasonably fast grinding passes of 5-7 seconds on an 18 " blade. Such grinding does not even warm the blade too hot to touch. Any grinding leaves sawtooth edges which are beneficial. (The barber's scissors are purposely ground with teeth). Stay off the back side of the blades except to remove the burr. Mower blades do not cut steak or scrape fine furniture wood. :2cents:

 

[motoman]

OK the first pic is a dull blade with (self inflicted) nicks.

The second pic is removing the nicks to have a uniform foundation in which to grind a 45 degree angle. Notice the grind is "square" to the bottom of the blade.

The 3rd and 4th pic is a view of this square grind

Edit:
Hmm, the pics show a different order on the post than when I uploaded, but you'll figure it out.

continued

Picture two is nice , but would be better if the "secondary" clearance were there. This is has also been called "slope" or "bevel".

 

[ScagRider03]

Threw together a video series on how to properly sharpen mower blades for anyone interested.

My blade sharpening video here (Part 1 of 2): https://www.youtube.com/watch?v=c0tuWqYE7BU
My blade sharpening video here (Part 2 of 2): https://www.youtube.com/watch?v=HgHsY_2Yqe0

Cheers!

Heck ya you used a flapper wheel that's honestly how I sharpen my blades never use a grinding wheel only flapper it does a great job in my opinion

 

[chance123]

Those of you that use a bench grinder, A "Ruby" stone is the coolest, and longest lasting stone.

 

[motoman]

Heck ya you used a flapper wheel that's honestly how I sharpen my blades never use a grinding wheel only flapper it does a great job in my opinion


Hey Scag Rider, How does a flapper remove metal required to sharpen? I thought a flapper was a deburr tool? :smile:

 

[enigma-2]

Please...bench grinders will not over heat if used properly. Clean wheel. Any wheel diameter . Grits of 46-80. Reasonably fast grinding passes of 5-7 seconds on an 18 " blade. Such grinding does not even warm the blade too hot to touch. Any grinding leaves sawtooth edges which are beneficial. (The barber's scissors are purposely ground with teeth). Stay off the back side of the blades except to remove the burr. Mower blades do not cut steak or scrape fine furniture wood. :2cents:

Grinders can get the blade too hot (a good example of this is some of the videos we see on You-Tube. In many cases it's evident those blades are being overheated.)

In most cases, I feel a lawn mower blade is best sharpened using a bastard file. (I switched to using a Work-Sharp for several reasons, not just lawn mower blades, but it is faster than filing, and the slower speed doesn't heat the blade appreciably).

I would however recommend using grinder if you see nicks in the blade. (A grinder will remove nicks in the blade much faster than you can file them.) Even so it becomes important not to overheat the blade. Another negative side-effect is that it's more difficult to follow the same angle of the original blade hand-holding a blade against a grinding wheel. The effect you see is a waviness after using a grinding wheel. You will not see this using a file (or Work Sharp).

Most home grinding wheels are usually in the 5"-6" range. Grinding with a small diameter like this has a tendency of producing a hollow ground effect on the blade. (Again, you will not have this problem using a file of flat grinder like a Work Sharp). Hollow grinding is good for a knife edge, bad for mowing grass (too little material at the edge). In such cases, I feel it better to leave more of an edge on the blade, perhaps as much as 1/8", to keep the thickness of the blade edge sufficient for hitting roots, rocks, etc.)

While I would also not recommend grinding hard on the backside, I feel a light grinding is beneficial to establish a true, flat edge. (This would not be possible using a bench grinder, but easy with a bastard file or Work Shape.) This is the point at which the edge of the blade is referenced from.

Lastly, I agree that lawn mower blades are not being sharpened to reflect the edge of a steak knife. New blades have an edge similar to that of a butter knife; which is exactly what we are trying to achieve.

Thanks for sharing you opinions,
Dennis

 

[chance123]

Most home grinding wheels are usually in the 5"-6" range. Grinding with a small diameter like this has a tendency of producing a hollow ground effect on the blade., bad for mowing grass (too little material at the edge).
Dennis

I sharpen (well, my employee does) 200+ blades a week and for me, a file is out of the question. After 40+ years in this business I have gone through several training seminars on sharpening and by experimenting and by Toro's recomendation, I have proved (to myself) that a hollow ground blade "lasts" FAR longer before it needs resharpening. I "strongly" suggest trying for yourself just like I did to see the truth in this method. I think you will be surprised just as I was. The difference is very noticable.

 

[motoman]

It is of course true any method of sharpening blades may be overdone to the detriment of the blade. I find I cannot remain silent on a couple issues. Anyone can put a grindstone to a blade and hold in one place until the geometric form is achieved. That form may be some desired angle or a hollow formed by the grindstone radius. If that is done without heat control the result is a burned, softened edge which will not hold up.

A hollow grind is a thing of beauty and I would prefer it , however...( I have never used a jig or guide for this) I bet besides an expensive grindstone ($25, $45, $ 55?) some sort of air , oil or water cooling is used as the stone "digs" out the hollow and then in a secondary pass the edge is put on.
Right? Beyond the scope of most home sharpeners. Incidentally, although a statement may have been made that manufacturers don't use this method my new Craftsman blade had a hollow grind which I was sorry to see go. I also see Wal Mart's array of blades where about half seem to have hollow grinds.

Next is the example with picture above of a jig ground blade where the edge is quite wide with no apparent burn. For that good result no doubt an expensive "friable" stone was used where the grains constantly break off to avoid over heat. Right ? Stones like Norton etc...? $35, $45 ? And a $300 jig?

You cannot use a Harbor Freight 60 grit grey wheel and do hollow or wide single angle edges without burning. What causes the softening is the dwell time on the blade to achieve the form. On a thick (150-.200") blade holding the angle while removing all the metal burns the cutting edge.

The technique to use while dry ginding with a cheap wheel is to grind the thick part first behind the cutting edge, and then the cutting edge. You can exert sufficient pressure on the grinder to remove the thick material (called secondary bevel by the pros), and then be much gentler when putting on the cutting edge which is a much narrower band. This technique narrows the blade. No burning should take place.

I believe all these different techniques and beliefs should be resolved once and for all. If you all can not agree with me then we need to hold a national "Grind Off" somewhere in Kansas or mid USA. The winner will get a years supply of his favorite abrasive....and I don't mean someone who has a different view. Happy grinding and keep your fingers safe.

 

[chance123]

I also think this topic is going a little too far.
In my field, working with professionals who mow 10 hours a day 6 days a week (probably 8 actual mowing hours per day) comes out to 48 mowing hours a week according to the hour meters. A commercial mower will run in "one day", what a home owner (mowing 2 hours a week) will put on in "one month"! They put on in one week, what a home owner puts on in six months! So for me, these things are very important to keep my clients machines in top shape the best I can. For a home owner, these things are less critical because of far less use. Here in Southern California, they mow 12 months out of the year, and they have many machines that are more than 5 years old and still running strong. With the ratio of hours between a home owner and a commercial, you can see that a 5+year old commercial has probably more continuous operating hours than most home owner machines that haven't already rusted out or a failure of some kind and not worth repairing. I am only sharing things I have learned and continue to learn. We all have different ways to our craft to reach the same goal. Happy grinding, flapping, and fileing.