How to Sharpen a Mower Blade

Having a sharp blade to mow the grass is important. A dull blade will tear and chew at the turfgrass, resulting in a whitish cast to the lawn. With a sharp blade, the mower is more efficient and uses less power. This segment shows step-by-step how to sharpen a lawn mower blade.

Produced by the Department of Communications at Kansas State University. For more information, visit our website at: http://www.kansasgreenyards.org

Transcript:
How to Sharpen a Mower Blade

Sharpening a lawn mower blade is important because it helps cut the grass neat and even. It prevents the white appearance that occurs on lawns when the lawn mower blade is dull – when it beats and tears the grass. Also, the mower runs more efficiently and cuts the grass better.

The first step in sharpening a lawn mower blade is to take the blade off. However, before you do anything, remember to remove the spark plug wire to prevent an accidental starting of the mower.

Next, turn the mower on it’s side. Turn it so the spark plug is up, so that the oil stays in the bottom of the engine. If you rotate it the other way, the oil could get into the cylinder head.

Take the blade off. I’m using a 9/16” socket and a breaker arm. Make sure that you don’t misplace the bolt and washer. There are some fairly dull surfaces here. It’s not too bad, yet. But, there are some fairly bad nicks on the cutting edge, and some debris. We’ll need to clean that up. I’m going to take it into the shop and put it into the vise and clean this debris before I begin to sharpen the blade.

First, I’ll put the blade in the bench vise before I start to work on it. I like to use a metal file to remove the debris. It has a nice sharp edge on the end to take the debris off the lawnmower blade. It’s important to remove the debris because I’m going to balance the blade after it’s sharpened.

Then, do the other side, and then I’ll be ready to sharpen the blade. Remember to put on goggles and hearing protection. I’ve ground the face of the blade down until I’ve removed most of the nicks on the cutting edge. I also want to make sure that I maintain the proper angle on the cutting face. It’s approximately a 60 degree angle. It looks pretty good, so I’m going to repeat this process on the other side of the blade.

The next step to sharpening the blade is to balance it. I’m going to mount this in my wood vise. I’ll bolt the blade to the bicycle wheel. If it’s perfectly balanced, it should stay fairly level. Let’s give it a little bit of wobble. It’s slightly heavy on the left side. To adjust for errors, I’ll flip it the other way and put it back on to see if it does the same thing. It’s slightly heavy on the left side again. So, I’m going grind a bit more of the surface off of this side of the blade to balance it.

I’ll check it out again – it looks good. I’ll flip it over to check it again. Now it has good balance. I’ll finish up the cutting edge with a file. File the back side a little bit to get all the rough edges off. The blade looks good, so I’m ready to attach it to the mower.

But, before I attach the blade, I noticed that there is quite a big of debris that has accumulated on the under side of the mower deck. So, I’m going to clean that off. This super bar tool makes an excellent tool for cleaning the underneath side of the deck. It has a nice, curved edge so that I can get in underneath, and it has a good edge for scraping.

I’m ready to reattach the mower blade. You’ll need to attach the blade firmly. It requires approximately 60 to 70 foot-pounds of force to tighten it. Then, turn the mower onto it’s wheels and reattach the spark plug. Remember that the blade will get dull fairly quickly – especially if you’re hitting a lot of debris such as gravel. So, the blade needs to be checked frequently. The blade should be re-sharpened after approximately ten to fifteen hours of use.

This feature story prepared with Jacob Weber, Kansas State University Research and Extension Horticulture Agent for Crawford, Cherokee and Montgomery counties. For more information, visit your local county extension office or visit our website at KansasGreenYards.org.