Sharpening Riding Mower Blades

It’s time to sharpen your riding mower blades and you don’t know where to start. We know that it can be daunting, so we thought we would put together a quick guide on sharpening riding mower blades.

Sharpening riding mower blades promotes an even cut and keeps your grass healthy. Before sharpening mower blades, make sure the riding mower cannot accidentally start by removing the spark plug boot. Depending on the make and model, you then either jack the rider up or remove the deck so you can access the riding mower blades to clean them and sharpen them.  

Now let’s take a look in further detail on how to sharpen your ride on mower blades.

Tools you need to sharpen a ride on lawn mower blade

  1. Work gloves and safety glasses,
  2. Sponge/washcloth and some warm soapy water should do)
  3. Usually a 15/16 socket wrench
  4. A  2-by-4 block of wood
  5. Vise Clamp
  6. Nail
  7. Hand file or angle grinder with metal abrasive disc
  8. Marking pen

Safety when servicing your ride on mower blades

Even old blades can have sharp points that can cut your hands. Always wear quality nitrile coated gloves when handling your ride on mower blades.

Move your mower to a hard, flat surface. Apply the brake.

To prevent accidental start up of your ride on mower while you’re working on the blades , remove the spark plug boot and drain the fuel. 

Accessing your riding mower blades

Depending on your riding mowers make and model, there a three basic ways to access the mower blades.

  1. Adjust your rider mower deck to the highest setting. Lay down on the floor and access the blades by reaching under the deck.  
  2. Jack up your mower using a hoist, floor jack or mower jack to give you enough room (also make sure your deck is on the highest setting before jacking it up). If using a jack, make sure you use the jack stands for safety. Make sure that the placement is correct, and it’s secure before sliding under it!
  3. Remove the deck to access the blades. You will need to lower the deck to the lowest position. Remove the belt guard, and then you can remove the belt from the pulley. Then you will need to remove the pins that hold the back of the deck – there is one on both sides of the deck. Next remove the front deck attachment point. Lastly you need to remove the PTO cable, there is a pin that secures it – so remove that first. Then pull the cable up and remove the spring. Now you can pull the deck out from underneath the mower, and flip it over to access the blades.

Can I sharpen blades while still on the riding mower?

You can sharpen mower blades while they are still on the mower, even though this is not the best way. Time how long you spend filing each blade to ensure you spend the same amount of time on each side. This will help you prevent ending up with unbalanced blades that can harm your rider.

But to get the best results, you are best off taking the blades off the mower to sharpen them. It is not much extra effort to remove the blades. And it makes it a lot easier to access the edges (you can clamp it into a workbench vice, rather than kneeling or laying on the ground)

Removing the lawn mower blades to sharpen then will give you better access to the blade for a steady hand and more polished job. It means that you can clamp it in a vice and focus on ensuring the angle is consistent the whole length of the blade.

But the most important reason to remove your blades when you sharpen them is so that you can check their balance once you’re finished. You can’t actually check the balance of your blades without taking them off the mower.

An unbalanced blade can actually damage your ride on mower. Listen for any unusual noises coming from under your mower deck next time you mow; you may need to take it somewhere to be serviced and ask them to balance it for you.

Removing riding mower blades

To remove the riding mower blades you will need your chock of wood, your 15/16 socket wrench, and your marker.

First reach under and mark the underside of the blades with your marker. This will ensure that you know which side of the lawn mower blade is up, so you can ensure that you reinstall them correctly.

The lawn mower blades are secured by a nut. The challenge is that when you turn the nut, the blade turns too. This is where your chock of 2×4 wood comes in handy. Place the chock of wood inside the deck to prevent the blade from rotating. Then you can loosen the nut with your socket wrench.

Give the rider mower blades a good clean

It’s no good trying to work with a blade that is covered in dirt, oil, or grass clippings, so get your cleaning gear and give them a good wipe down.  Once they are clean and shiny, dry them off with a clean cloth.

Sharpening riding mower blades

First you want to clamp your bar blade in the vise. This will allow you to focus on getting ensuring you sharpen the blade evenly along the length of the blade.

No matter what sharpening tool you use, try to spend the same amount of time on each end while sharpening so that you don’t take more metal off one than the other. This will help you prevent your blades from becoming unbalanced

Sharpen mower blades by hand

You can now sharpen your riding mower blade by hand using a file. If you are wondering what angle should lawn mower blades be sharpened at, it is quite simple. The angle of each blade can be a bit different, so just follow the angle of the original edge.

Sharpen mower blades with angle grinder

An angle grinder with a metal abrasive disc is a faster option for sharpening ride on lawn mower blades if you have one on hand. Once again be sure to follow the angle of the existing edge.  Use smooth, even strokes from the inside to the outside edge of the blade. 

When using an angle grinder, make short passes over the mower bar blade, and be careful that it doesn’t get too hot. Grinding the blade causes friction, which generates heat. Too much heat will weaken the metal of the lawnmower blade and could cause it to warp, or not hold its edge for as long.

How sharp does a mower blade need to be?

You only need to sharpen your lawn mower blade to about the sharpness of a butter knife. When the metal blade spins so fast, it doesn’t need to be razor sharp. In fact, over sharpening can weaken the edge and the blade will dull and dent faster.

Do you need to balance mower blades?

Imbalanced mower blades can cause extra wear and tear on your ride on mower so it is important to make sure your mower blades are balanced after sharpening them.

An unbalanced blade usually occurs when more metal is filed off one side than the other. When a mower blade is spinning extremely fast (around 4000RPM) it causes vibration and unnecessary stress on your on your rider’s mower frame, blade shaft, bearings, spindle and engine. Ultimately it can cause damage that is costly to fix.

So how do you balance a lawn mower blade?

This is where your nail comes in handy. Clamp your nail into the vise. With the blade held horizontally, hang it through the centre hole onto the nail. When you let go, watch to see if it balances, or tilts to one side. If it’s heavier on one end, then that end has too much weight, and you’ll need to grind more off.

Putting your ride on lawnmower back together

Now you just need to backtrack and put everything back on your riding mower the opposite way you took it off. Make sure you install the blades the right way up- this is where those markings will come in handy.

Also ensure that you tighten your ride on’s blade nuts firmly so they can not vibrate loose with use. Your chock of 2 by 4 wood will help you once again in preventing the blade from spinning.

Don’t forget to reconnect the spark plug boot / cap- so you don’t wonder why your lawn mower won’t start next time you use it!

If you need any help, our mechanics can sharpen your ride on mower blades for you. Just bring your rider in store so we can help you out!

Other Q&As

Why should I sharpen mower blades?

Dull mower blades don’t cut well and you’re more likely to tear the grass. This isn’t good for the health of the lawn as it leaves it open to fungal infection. It also doesn’t give it a nice clean, even cut appearance.

How do I know when my mower blade is dull?

If the tips of your grass look messy and torn, rather than cleanly cut after you have mowed, it’s a sign that your lawnmower blades may need sharpening or replacing.

How often should mower blades be sharpened?

Mower blades should be sharpened every 20-25 hours of use. Therefore, if it takes half an hour to mow your yard, and you do it once a week, then you should sharpen them once a year. If you do an hour of mowing a week, sharpen them twice a year.

Newsletter Updates

Enter your email address below and subscribe to our newsletter