Sharpen a knife, an axe and a mower blade the same way

All three jobs come down to one thing: raising a burr along the full length of the edge, then removing it cleanly. Everything else is bookkeeping. Which angle, which grit, whether you use a 10-inch mill bastard file or a coarse diamond plate, is a detail. If you haven't raised a burr, you haven't sharpened anything. You've polished a dull edge and made it shinier.

A burr is the thin lip of metal that folds over to the far side when you've finally ground past the worn part of the edge. You find it with your thumb, dragged off the edge, never along it. It feels like a tiny catch or a hangnail. On a kitchen knife it's almost invisible. On a mower blade you can see it from a meter away.

Learn to feel for it once and you'll never need a sharpness gadget again.

Before you touch anything

Gloves on your non-working hand for the axe and the mower blade. Not for the knife, where a glove kills your feel for the angle and you're moving away from the edge anyway.

For the mower, pull the spark plug lead off and tape it back so it can't flop onto the plug. On a battery mower, take the battery out and put it on the other side of the garage. A gas mower tipped the wrong way floods the air filter with oil and sometimes fuel, so tip it with the carburettor and air filter facing the sky, or drain the tank first. Get that wrong and you'll spend Saturday morning cleaning a filter instead of cutting grass.

Work at a height where you're not hunched. Sharpening badly is mostly a posture problem.

The knife

Kitchen knives and pocket knives want somewhere between 15 and 20 degrees per side. Twenty is a good default. If you can't picture 20 degrees, stack two 20p coins under the spine of the blade with the edge on the stone. That's close enough to start.

Use a coarse stone first if the edge is properly gone, something in the 220 to 400 grit range. If it's just tired, start at 1000. Soak a water stone for ten minutes. Diamond plates need nothing but a squirt of water.

Pick one side. Push the edge into the stone as though you were shaving a thin slice off the surface, leading with the edge, and work from heel to tip in overlapping passes. Keep the angle steady. The angle mattering more than the pressure is the whole game, and most people push far too hard and rock the blade at the same time.

Now the part people skip. Stay on that one side until the burr runs the entire length of the blade, tip included. Check with your thumb every ten strokes or so. The tip is always last, because the blade naturally lifts as you come round the curve. Slow down there and drop your elbow.

Once the burr's continuous, flip the knife and do the same on the other side. The burr will fold back over. Then take the pressure right off, alternate sides, and do five or six light passes each way to break it off. Finish on a finer stone if you have one, 3000 or 6000, or ten passes each side on the back of an old leather belt.

Test on paper. Hold a sheet of newsprint in one hand and cut down through it. A sharp knife bites in and glides. A dull one tears and folds. If it grabs at one point along the blade, you missed that inch with the burr.

The axe

Different problem. An axe edge isn't a flat V, it's a convex curve, and that curve is what stops it wedging in green wood. If you put an axe on a bench grinder you will do two things: thin the bevel to a shape that folds over on the first knot, and blue the steel, which removes the temper for good. A blued edge never holds again. You can grind past it, but it's an hour of work you didn't need.

So: a file. A 10-inch mill bastard file with a proper handle on the tang, and a file card to clean it. Files cut on the push only. Dragging them back over the steel dulls the teeth.

Clamp the axe head in a vice with the edge up, or lay it flat on a bench with the head hanging over the edge and a knee on the handle. Work from the edge back into the cheek, pushing the file across the bevel, and follow the existing curve rather than imposing a flat one. You're aiming for roughly 25 to 30 degrees inclusive on a felling axe and a bit more on a splitting axe, which wants to be blunter than you think.

Same rule as the knife. File one side until there's a burr all along, then turn it and do the other. Count strokes if it helps you keep them even.

Then take a puck, the round double-sided sharpening stone every hardware shop sells, and work it in small circles over the bevel with the coarse side, then the fine side. Move the stone, not the axe. Keep your fingers behind the edge.

A felling axe should shave hair off your forearm. A splitting maul shouldn't, and doesn't need to.

The mower blade

Take the blade off. Mark the underside with a paint pen or a scratch before you loosen the bolt, because fitting it upside down is the single most common garden mistake and the mower will still run, badly, throwing grass nowhere and cutting nothing.

Wedge a block of wood between the blade and the deck so it can't spin while you loosen the bolt. It'll be tight and often rusted.

Clamp the blade in a vice. Keep the factory bevel, which on most rotary blades is around 30 degrees, and just refresh it. A file works fine and is quieter than you'd think. An angle grinder with a flap disc is faster but takes metal off in a hurry, so keep it moving and dip the blade in water if it changes color.

Don't sharpen it to a razor. Leave a land about the thickness of a credit card edge. A knife-sharp mower blade chips on the first stone and rolls over within an hour.

Now balance it. Hang the blade on a nail driven into the wall, through the center hole. If one end drops, file metal off that end's bevel until it sits level. An out-of-balance blade shakes the spindle bearings apart over a season, and you'll hear the vibration long before you can afford the repair.

Refit it the right way up, with the cutting edges leading in the direction of rotation and the lift wings pointing up into the deck. Tighten to the figure in your manual.

What actually goes wrong

Grass that goes pale brown at the tips two days after mowing is a blunt blade tearing rather than cutting. That's your reminder, and it comes round about every 20 to 25 hours of use.

A knife that slides off a tomato skin has a rolled edge, not a worn one, and often needs nothing but a honing steel used at the same 20 degrees with almost no pressure.

And an axe that bounces has usually been sharpened into too thin a wedge by somebody trying to make it a knife.

Do one of the three this weekend. The stone doesn't care which.