How to Sharpen a Plane Iron on Waterstones: Camber vs Straight

This is catching the MOAM's attention today….. a plane that skates, chatters or leaves little ridges across the board almost always has an edge problem, not a plane problem. I've got cedar and white oak to plane for the dory this fall, so today it's the whole routine for a bench-plane iron on waterstones, plus the question that starts an argument in every shop on the North Shore: do you put a curve on the edge, or keep it dead straight? Short answer: it depends on the plane.

Why it matters: A sharp edge is just two polished surfaces meeting, the bevel and the back. Lee Valley and Lie-Nielsen both start there. Skip the back and you get a row of tiny saw teeth that dull in a few strokes. The shape of the edge matters just as much. A smoothing plane with a square iron digs its corners into any board wider than the blade and leaves ridges Chris Gochnour (Fine Woodworking) calls tracks. A rabbet or shoulder plane with a curved iron can't cut a clean, square corner. Smoothing a wide oak plank for the dory, I want the first one curved. Cleaning up a rabbet in the stem, I want the second one straight.

Materials

• Waterstones: a 1,000 grit to raise a burr and an 8,000 to polish, with a 4,000 in between if you like. Christopher Schwarz runs 1,000/4,000/8,000; Lie-Nielsen teaches 1,000 and 8,000–10,000. A 1,000/6,000 combination stone is a fine way to start.
• Wet/dry sandpaper, 100–220 grit, on something flat (granite, a machine bed, ½-in. float glass), or a coarse diamond lapping plate, to flatten the stones
• A thin steel ruler, about 0.020 in. (0.5 mm) thick or less, for the ruler trick
• A pencil, for the flattening check
• Rust protection: light oil (Lie-Nielsen uses jojoba), Boeshield T-9 or paste wax (Lee Valley)
• A scrap board wider than the iron, for test cuts

Tools

• A side-clamp honing guide. A narrow single-roller (Eclipse-style) guide rocks easily, which helps when you're cambering (Gochnour).
• A protractor, or a stop board, to set 25° and 30° the same way every time
• A combination or engineer's square, and a feeler gauge (the same one you gap spark plugs with) to read the camber
• A straightedge for checking the stones
• A strong light, and a loupe if your eyes are like mine

Steps

1. Flatten the stones first. Draw a pencil cross-hatch on the face, then rub the stone on wet/dry paper (100–220 grit) stuck to a flat surface, or on a diamond lapping plate, until the lines are gone. Lie-Nielsen says that's about 15–20 strokes; turn the stone 180° now and then. Check it with a straightedge. Waterstones wear fast, and a dished stone will curve your edge whether you asked for it or not, so flatten again at the end of every session. David Charlesworth keeps his coarse stones in a tray of water (stored dry, they want about a five-minute soak) and just sprays the 4,000 and finer. Glass-backed Shaptons get a spritz, never a soak (Lie-Nielsen's Deneb Puchalski, FWW).
2. Get the back flat where it counts. On a plane iron, the back only has to be flat and smooth near the edge. Lee Valley laps it on an 800 or 1,000 stone, then polishes on a 4,000 or 8,000. Puchalski's goal is a flat back with no heavy milling marks running out to the edge, about 5 to 10 minutes on sandpaper. Don't spend an afternoon polishing the whole thing.
3. Use the ruler trick on the back. This is David Charlesworth's. Lay the thin ruler along one long edge of the 8,000 stone. Lay the iron bevel up across the stone, back resting on the ruler, edge on the stone. That tips the back up less than 1°; Charlesworth figures his 0.5 mm ruler gives about two-thirds of a degree. Stroke on and off the end of the stone, and don't bring the edge more than ½ in. onto it (Lie-Nielsen). Stop when you see an even mirror band about 1/32 in. wide, corner to corner (Puchalski). This is for plane irons only. Never do it to a chisel; a chisel needs a flat back (Lie-Nielsen).
4. Hone a 30° secondary bevel on the 1,000, and feel for the burr. Most bench-plane irons come ground at about 25° (Lee Valley, Lie-Nielsen). Set the guide for 30°. Puchalski: "For the most common primary bevel of 25°, a secondary bevel of 30° works well." Paul Sellers hones his at 30° too. Lie-Nielsen's own basic method goes to 35°, a 10° secondary, and Lee Valley lists 30°–35° for hardwood with pin knots. Four or five passes should raise a burr, a wire edge you can see and feel on the back. The burr test: slide a fingertip across the back and off the edge (never along the edge). You want a faint catch the whole width of the iron. If one corner has no burr, the bevel hasn't reached the edge there yet. Keep going.
5. Smoothing plane? Camber it with finger pressure. Still on the 1,000, press down hard at one corner for a set of strokes, then the other corner, then partway in from each corner, then a few in the center. Schwarz does 10 strokes at each corner, 7 at each in-between spot, and a few in the middle. Lie-Nielsen does 6, 4 and 2. More strokes at the edges than the middle takes more steel off the corners and leaves a gentle arc. Hold the iron against a square: you should see a little light at each corner. How much? Not much. Gochnour says 0.001 to 0.002 in. on a smoother; Lie-Nielsen's routine gives .002 to .005 in.; Schwarz measured .006 in. at the corners of his favorite No. 4 with a feeler gauge.
6. Jack or fore plane? A lot more camber. These are the planes that take the heavy cuts. Schwarz puts an 8-in. radius on his fore plane, and says 8 to 10 in. is typical on a jack. By my math, on a 2-in. iron that's roughly 1/20 to 1/16 in. of sweep back at the corners. That's grinder or coarse-stone work (Schwarz grinds his), then you hone it the same way. It's how you hog a cupped cedar plank down without the corners digging in.
7. Shoulder, rabbet and block planes: straight and square. Lee Valley is blunt about it: joinery planes like rabbet planes are never cambered or given rounded corners, and the edge has to stay square to the sides of the blade. Lie-Nielsen says shoulder planes need a straight edge too. Schwarz lumps block planes in with chisels: sharpened straight across. Even pressure across the guide, and check it with the square. Jointer planes are your call: Lie-Nielsen keeps theirs straight, and some guys add a hair of camber to help square up an edge.
8. Polish on the 4,000 and 8,000, then kill the burr. Same pressure pattern if you're cambering. Puchalski takes four or five passes on the 8,000 and stops when he sees a clean, bright line of even width right at the tip. If it's wider at one corner, your pressure was uneven; a few extra strokes on the narrow side fixes it. Then go back to the ruler trick on the 8,000, about 10 passes on and off, to take the burr off the back (Lie-Nielsen). Put it in the plane, set a light cut and look for see-through shavings.
9. Dry it, oil it, and know when to regrind. Water and steel don't mix, and Marblehead salt air doesn't help. Wipe the iron dry the minute you're done and oil it. Over time the 30° bevel gets wider; when you're taking 20 to 30 passes on the 8,000 to get an edge, Puchalski says it's time to regrind the 25° primary. Lie-Nielsen leaves about 1/64 in. of the old secondary so the square edge stays defined.

MOAM's shop note: The most common mistake I see is too much camber on the smoother. You get a skinny little shaving out of the middle of the mouth and spend all day making passes. Gochnour's rule: if the shaving's narrow, put more strokes in the center; if you still see tracks, put more on the corners. A good smoother shaving is nearly full width and fades to nothing at the edges. Sneak up on it. It's a lot easier to add camber than take it out. That's my own practice, not a number from a book. And pro trick for a New England shop: Charlesworth keeps his coarse stones soaking in a tray, but if your shop freezes at night, don't store them in water. He says they'll shatter. Come November in Marblehead, mine come in out of the cold.

Sources: Lie-Nielsen Toolworks, Sharpening Instructions (rev. 08/2023) and Shoulder Plane instructions; Deneb Puchalski, "Get Sharp—Fast," Fine Woodworking #213; David Charlesworth, "A User's Guide to Waterstones," Fine Woodworking #169, and his "Ruler Trick" video; Thomas Lie-Nielsen, "Sharpening a Plane Iron that has a Pitted Back," Fine Woodworking; Chris Gochnour, "Camber: The Secret to Perfect Planing," Fine Woodworking; Christopher Schwarz, "Camber With a Honing Guide," "Coarse, Medium & Fine," "Yes, You Need a Jointer and a Jack" and "Super-specific Smoothing Plane Specs," Popular Woodworking; Lee Valley/Veritas, Sharpening System instructions, "Getting Started With Your Jack Rabbet Plane" and "Getting Started With Your Veritas Bevel-Up Bench Plane"; Paul Sellers, "One System Fits All" and "Setting your plane after sharpening."

MOAM Out.

Tools for this tip

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• King KDS 1000/6000 combination waterstone: a 1,000 side to raise the burr and shape the camber, a 6,000 side to polish
• DMT Dia-Flat diamond lapping plate (4 x 10 in.) for flattening waterstones: keeps the waterstones dead flat so they don't put a curve in your edge you didn't ask for
• Starrett 12-inch combination square (11H-12-4R): holding the iron to the blade to check the camber, or that a rabbet iron is straight and square
• iGaging 6-inch digital caliper: checking your ruler-trick ruler is about 0.020 in. thick
• The Complete Guide to Sharpening by Leonard Lee (book): the standard reference on sharpening

Use whatever you already have in the shop; these are just the ones that fit this job.