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

Mar 31
6 min read

Updated: Jun 11

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.

BLADE HOLDERS FOR SHARPENING AND HONING

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:

12 degrees is the original angle of the Mammotion blades. This 12 degree holder is used for Step 1 of the sharpening process.
- Sharpen the blades on a 600 grit diamond stone.
20 degrees is the honing angle. This 20 degree holder makes a very small bevel on the edge that is stronger and more durable than the 12 degree angle. It also makes the sharpening process faster, because there's less material to remove at 20 degrees vs 12 degrees.
- Hone the blades on a 1200+ grit diamond stone.
- This is what the blade edge should look like after this step. The 20-degree micro bevel can be seen as the bright, shiny part at the edge.

Close-up of a finger holding a rusty metal razor blade with two round holes against a plain background.

The underside of the blade holder with the blades installed:

Knife sharpener and white blade guide on a wooden workbench, with a screwdriver and tool parts nearby.

Blades bening sharpened on a portable diamond sharpener. It's not as wide as the blades, but it still works.

White 3D-printed clamp on a black rail atop a worn wooden workbench, with an orange container blurred in the background.

Blades being sharpened on a large diamond plate. This works a lot better. Wet the plate to allow the particles to clean off better and speed up the sharpening.

Close-up of a sanding block holding a white 3D-printed part with a green knob, labeled 600 Grit, on a work surface.

HOW TO ASSEMBLE THE BLADE HOLDERS

HARDWARE:

You will need the following hardware:

10-32 x 1.25in Flat Head Screw
10-32 Nut
8-32 hardware will also work, but will be loose.

ASSEMBLY:

This exploded view shows how the parts come together.

Exploded diagram of a 3D printed lawnmower blade sharpener with blade clamp, spring, knob, nut, and screw labels.

How to insert the blades:

Three-step diagram of a UBA blade holder: loosen, insert blades, then tighten thumbwheel; gray tool with blue blades and labels.

SHARPENING STONES

Large, flat diamond sharpening stones are the best to use for sharpening these blades. There are cheap ones that are ok, and expensive ones that are excellent.

I recommend buying at least these 2 grits of stones.

600 grit - for sharpening at 12 degrees
1200 grit - for honing at 20 degrees

CHEAPEST DIAMOND SHARPENING STONES

If this is all you're planning to use the diamond stones for, then buy a cheap set like these. This is a double sided stone with 600 grit on one side and 1200 grit on the other. Don't expect this to last as long as the nicer stones, but it's probably good enough for casual use.