A step-by-step guide for sharpening your mower blades

posted on Monday, November 19, 2018 in How To

Make your riding mower the sharpest tool in the shed

It’s no surprise that if you cut your own grass you have the gumption to maintain your own mower. We’re glad you came here for the necessary know-how on sharpening your mower blades. The experts at John Deere have laid out the process in a few straightforward steps.

Blade sharpening must-haves:

  • Floor jack
  • Ratchet - preferably pull-handle with 6-point sockets
  • Table vise
  • Hand grinder with medium stone
  • Safety glasses
  • Blade balancer (store-bought or homemade)

Blade sharpening "nice-to-haves":

  • Wooden board (2x4)
  • Work gloves

1. Lift your riding mower

Place a floor jack (available at auto parts stores) underneath the front of your riding mower, making sure it makes contact at the proper lift points. Raise the mower as high as the jack will lift it, securing your equipment with jack stands underneath for stability. Now you can easily access the bolt, securing the mower blade to the mowing deck. Whether you have a riding mower or a tractor with a separate mowing deck, our experts recommend jacking up your equipment and not trying to remove blades from a deck that isn’t attached to your tractor.

sharpen-mower-blades

lift-mower

2. Remove the blade(s)

Match the correct sized 6-point socket to the bolt securing the mower blade to the deck, then attach the socket to your ratchet. 6-point sockets will fit John Deere bolts more securely than 12-point. Optional: place a wooden block against the mower blade and the mowing deck to stabilize the blade while you unscrew the bolt. Twist the bolt counter-clockwise to remove it and put it in a secure place. Repeat, as necessary, for multiple blades.

lawn-mower-blade-sharpening

Before removing it, you may want to mark the bottom of the blade with a touch of chalk, paint, etc. to remember which way it goes back on after you have sharpened it. If you have multiple blades, you may want to mark them to indicate which side of your mower they came from, though it’s likely John Deere mowing blades are stamped “left” and “right.”

3. Secure the blade in a table vise

Open the vise so it is wider than the widest point of the blade. With the blade parallel to the ground, tighten the vise around the center of the blade, so equal portions are exposed on either side.

blade-table-vise

4. Sharpen one side of the blade

Here’s some helpful background info from our experts before you start sharpening. Unlike with a kitchen knife, you don’t sharpen a mower blade until it can slice paper or comes to a fine point. You want to go over it with a hand grinder until it takes on a shiny finish. Color is your indicator, not sharpness or thickness.

dull-blade

sharp-blade

Now, put on your safety glasses.

Make sure your hand grinder has a medium stone in place (not a fine or coarse stone). When your grinder contacts the blade, make sure they make contact between a 45–65-degree angle. You want your hand grinder running at full speed when it contacts the mower blade. You can move the grinder in either direction along the blade as long as (important!) you maintain even pressure on the blade.  Make sure the grinder throws sparks away from you. Lastly, be sure you only sharpen the top side of a mower blade.

Move the grinder at a fairly moderate pace so you don’t leave the grinder in one spot for too long, which can overheat the blade. You do not want any portion of your blade to start turning black. Remember, you don’t need to make your blade sharp on the first pass; in fact, it’s better to go gradually and make as many passes as you need.

Make measured passes with the grinder running full speed until this half of the mower blade has a shiny finish. Under no circumstances should you test the sharpness of the blade with your finger or any object.

blade-pass

5. Sharpen the other half of the blade

Loosen the vise and rotate the blade 180 degrees so the other side is exposed and ready to sharpen. Repeat the process from step 4 until this side of the blade is shiny.

If you have multiple blades, repeat steps 4 and 5, as necessary, until all mower blades are sharpened.

6. Balance the blade

After you’re finished sharpening your blade(s), check that it’s balanced before reattaching it. An unbalanced blade can cause vibrations while you mow, which makes for an uncomfortable ride. If a blade is severely unbalanced, it can even cause stress cracks in your mower deck.

blade-balance

Blade balancers are inexpensive and widely available in lawn mower maintenance shops. Place your balancer on a level surface, then place your blade onto it, lining up the blade’s center hole over the balancer’s point. If the blade leans to one side, that side needs additional sharpening to remove excess material. So, put it back in the vice, and make more passes on that side with your hand grinder. Then re-check the balance.

If you can’t find a blade balancer or want to make your own, secure a screw or nail in a wall parallel to the ground. Hang your sharpened blade on it, making sure the nail or screw supports the blade by its center hole. If it hangs level (parallel to the ground), it’s ready to reattach. If not, put it back in the vice and make more passes on that side. Recheck the balance before proeceeding.

7. Replace the blade(s) on the mower

After your blades are sharpened and balanced, retrieve the bolt(s). With your lawn equipment still raised by the floor jack, put the blade back on in the same position it was when you took it off (look for that touch of chalk you applied to the bottom). Insert the bolt and tighten it by turning your ratchet, with the 6-point socket, clockwise. Optional: use the wooden block to keep the blade stable while you tighten the bolt. Do not over-tighten the bolt. Repeat as necessary for every blade.

8. Lower your riding equipment

Remove the jack stands from underneath your equipment. Slowly lower the floor jack, bringing your lawn equipment back to the ground—then pull the jack out from under it.

Congratulations on earning your blade-sharpening merit badge! If you have any questions about this process, or if you want to make sure you have the best kind of blades for your mower, reach out to the experts at your closest John Deere TriGreen location.

On the other hand, if this seems like too much for you, if you’re not in the market for a floor jack, or if you just don't have the time, then it's time to TriGreen! Our techs would be happy to help. Schedule your blade sharpening service today.