How To Sharpen Robot Lawnmower Blades with 3D Printed Sharpening Tool and Diamond Stones - For Mammotion Luba, Yuka and other robotic lawn mowers

The blades that come on robotic lawnmowers like the Mammotion LUBA and YUKA are different from the large blades on a traditional gas mower. Robot lawnmowers use small, thin razor-style blades and rely on their sharpness for cutting because the decks have much less power than a gas mower. A traditional-style mower needs a sharp blade, too, but its sheer power can cut and mulch grass even when the blade is a little dull. A robot lawnmower needs a razor-sharp blade to keep cutting well; otherwise, it will start tearing up the grass or not cut at all.

Replacement blades are affordable, but throwing away blades unnecessarily is wasteful if they can be resharpened several times before disposal. I've been using the original blades for 4 years in the Mammotion LUBA by simply taking a few minutes to resharpen them every few months of use.

I have spare sets that are already sharpened and swap them with the dull sets and then resharpen them on the workbench while the mower continues to cut grass.

To make sharpening easy, I designed a 3D printable holder that holds 2 blades. Both blades are sharpened simultaneously.

WHERE TO DOWNLOAD 3D PRINT FILES

• MAMMOTION LAWNMOWER BLADE SHARPENER 3D FILES

I prefer a dual bevel sharpening process (explained in further detail below), so I designed 2 holders:

1. 12 degree holder sharpens the blade at the original 12 degree angle.

2. 

   20 degree holder to hone the blade edge.
   

   

The blades are sharpened on 2 edges. This makes them easy to install, because it doesn't matter which direction you install them on the mower deck. However, don't assume that it gives you more cutting edges. My experience is that by the time the cutting edge is full, the other edge is also full due to wear. Therefore I pick the best edge and only sharpen that one edge, because sharpening the other edge is a waste of time.

• The sharpening angle on a stock Mammotion blade is 12 degrees. The white holder is set to 12 degrees.

• Use a 600 grit diamond stone to resharpen.

• Sharpen on one side until enough material has been removed to start forming a fresh edge.

• Loosen the holder and flip the blades.

• Sharpen on the other side until a sharp edge begins to form.

• Make sure that you sharpen evenly on both sides. Usually this is pretty quick, taking less than a minute per side. If the blade is damaged or severely dull it may take more time and material removal.

• Once a reasonably sharp, clean edge is created, it's time to start honing on a finer diamond stone, like a 1200 grit.

• Honing on 1200 grit stone can be done at the same 12 degrees angle, but will take longer due to the small amount of material removal. A faster method is to use the dual bevel or micro bevel sharpening technique.

• Remove the blades and install them in the 20 degree 3D printed holder.

• Hone the blades at 20 degrees on the 1200 grit diamond sharpening stone. Be careful to not over do it, as this will go very quick.

• Loosen the holder, flip the blades and hone the other side at 20 degrees on 1200 grit.

• A small, even edge should be visible at the top of the edge of the blade, as shown here.

• Stop when it looks like the image below.

• Use a leather strop with polishing compound, drag the blade backwards several times on both sides on it at about 20 degree angle to remove the burr and clean and polish the edge.

• With practice, this process only takes a few minutes and blades aren't wasted.

Dual Bevel Blade Sharpening

Dual bevel, micro bevel, dual angle, etc blade sharpening is a sharpening technique that makes it faster to sharpen a blade, and makes a stronger, more durable edge.

In this example (for kitchen knives), we begin by coarse sharpening at 15 degrees to create an edge. This sharpening only needs to be taken up to 600 grit. Then the blue lines are honed at 22 degrees using 1000+ grit. This creates a very small edge at a larger angle that is more durable than the narrower angle edge was. Since it is very small, it doesn't compromise the ease of cutting, because the main wedge effect is still at 15 degrees. Each consecutive honing removes material to the next set of blue lines. Eventually you're left with a large surface area 22 degree angle, which does make cutting less efficient due to the larger wedge angle and takes more time to remove material with the hone.

At that point it is time to resharpen to 15 degrees.

Then repeat the 22 degree honing steps again.

After honing, always use a strop to remove burr and clean and polish the edge. The strop should be used with an angle equal to or slightly less than the honing angle.