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A plane iron is a wedge with a job description. The bevel angle sets clearance beneath the cut, the micro-bevel sets how quickly the edge can be restored, and the camber decides which part of the iron touches the wood first.
Sharpening arguments usually start with grits and jigs, but geometry does more for the cut than abrasive choice. An iron honed at the wrong angle will not hold up in hard maple, an iron with too much camber cannot smooth a panel, and one with none will leave ridges.
This guide covers the angles, the camber amounts that belong on each plane, and how to check an edge before it touches wood.
The Three Angles That Define an Edge
The bevel angle is measured between the flat back of the iron and the honed face. A 25-degree bevel is the traditional starting point; 30 degrees is common for hardwoods and for bevel-up irons that need durability. The back must stay flat, because a rounded back produces a rounded edge.
Clearance is the angle between the bevel and the wood beneath it. On a bevel-down plane, clearance equals the frog angle minus the bevel angle. A 45-degree frog with a 25-degree bevel gives 20 degrees; a 30-degree bevel gives 15. Below about 10 degrees the heel of the bevel rubs and the plane skates.
On a bevel-up plane the effective cutting angle equals the bed angle plus the bevel angle. A 12-degree bed with a 25-degree bevel cuts at 37 degrees, which is why low-angle planes handle end grain so well. The same plane with a 35-degree bevel cuts at 47 degrees.
The Primary Bevel: Clearance and Support
The primary bevel does two jobs: it provides clearance behind the edge and supports the thin metal at the tip. A bevel that is too thin for the wood crumbles under load; one that is too steep takes more effort to push and can make the plane skip.
For most bench planes in domestic hardwoods, 25 degrees with a 30-degree micro-bevel is a good compromise. The lower primary grinds quickly, and the 30-degree tip gives durability with 15 degrees of clearance. Softwoods cut more freely at 25 degrees. Hard maple, white oak, and other dense woods favor a 30-degree primary, at the cost of some clearance.
Bevel-up planes need more thought because the bevel is the cutting angle. A 25-degree bevel on a 12-degree bed is a 37-degree cut for end grain. A 30-degree bevel gives 42 degrees for general work, and a 35-degree bevel gives 47 degrees for figured wood.
The Micro-Bevel: Small, Fast, Repeatable
A micro-bevel is a narrow secondary bevel, 1 to 2 degrees steeper than the primary, honed only at the tip. It should be 0.005 to 0.020 in wide, which is a few strokes on a fine stone. The rest of the bevel stays untouched.
The advantage is speed. Honing a micro-bevel removes a sliver of metal instead of repolishing the whole face, so an edge can be restored in under a minute. Its presence also tells you that you are honing at the intended angle. When the micro-bevel grows wider than about 1/32 in, regrind the primary and start again.
Keep the micro-bevel consistent. Alternating between 25 and 35 degrees rounds the bevel and shortens edge life. Honing guides versus freehand sharpening covers how to hold the angle with or without a jig.
Camber: What It Does
Camber is the curve ground across the width of the iron. It changes the cut in three ways: the middle of the iron takes a heavier shaving than the edges, the corners stop digging tracks, and the plane can remove a high spot selectively.
The amount is measured as the difference in projection between the center of the edge and the corners. A smoother needs almost none, a jack needs enough to hog off a high spot, and a scrub needs a pronounced curve. Too little leaves tracks; too much leaves a scalloped surface.
Camber is not the same as easing the corners. A 1/64 in chamfer on each corner stops tracks on a smoother while keeping the edge essentially straight. A full camber is a shape for stock removal, not a substitute for sharpness.
Camber by Plane: Scrub, Jack, Smoother
A scrub plane removes material fast. Its iron is typically 1-1/2 to 1-3/4 in wide with 1/16 to 3/16 in of camber across the width, a radius of roughly 5 to 7 in. That curve produces a scooped shaving and a surface of shallow valleys, ready for the jack plane. Scrub and fore plane stock removal explains the sequence.
A jack plane is the transition tool. About 1/32 in of camber across a 2-in iron, roughly a 16-in radius, lets it take a heavy cut in the middle and feather at the edges. That removes the scrub plane's ridges without cutting a deep groove.
A smoother needs the least camber: 0.001 to 0.003 in across the width. The goal is an even shaving with no tracks, so the edge is nearly straight and only the corners are eased. A smoother with a jack's camber leaves a rippled surface.
Grinding vs Honing
Grinding shapes the bevel; honing sharpens the tip. A 6-in wheel leaves a hollow grind, and the concavity reduces the steel touching the stone while helping the bevel sit flat. Grind at the primary angle, then hone a micro-bevel 1 to 2 degrees steeper.
Heat is the enemy. An edge heated until it turns blue has lost temper and will not hold up. Use a slow-speed grinder or a CBN wheel, dip the iron in water every few seconds, and keep a finger close to the edge to feel the temperature. If the edge discolors, grind back past the affected metal.
Hone on a progression that suits the steel: 1000 grit to establish the micro-bevel, 4000 to refine it, and 8000 or a strop to polish. Water stones, oil stones, and diamond plates compared covers abrasive choice, and stropping covers the final polish.
Checking the Edge Before It Touches Wood
Check square first. Stand the iron on its back and sight along the edge, or hold a small square against the back and the edge. A skew of 1/32 in across a 2-in iron is enough to pull the plane off line, and the lateral lever cannot fully compensate.
Check camber with a straightedge held across the edge. On a smoother the gap at each corner should be barely visible, no more than 0.002 in. On a jack it should be about 1/32 in, and on a scrub it should be obvious. An uneven camber makes the plane pull to one side.
Check for a wire edge. A burr left by honing folds over in use and leaves a ragged surface. Pull the edge lightly through scrap wood or give it a few passes on a strop. Do not test sharpness with your thumb.
How Edge Geometry Steers the Plane
A cambered edge contacts the wood over a shorter chord than a straight edge, so the effective width of the cut is narrower than the iron. That is why a jack with 1/32 in of camber can take a heavy shaving without stalling: the middle does the work and the edges barely touch.
The same geometry explains why a smoother with too much camber leaves a scalloped surface. The plane rocks across the crown of the camber, and each pass leaves a shallow groove.
Camber also affects steering. A symmetrical camber runs straight; an asymmetrical one pulls toward the heavier side. On a bevel-up plane the camber is ground on the bevel, so the cutting angle varies slightly across the width. Keep camber modest on a block plane.
Troubleshooting Edge Problems
Tracks or ridges. The iron corners are too sharp, or the camber is too shallow. Break the corners on a stone or increase the camber. If tracks persist, check that the iron sits square in the plane and that the sole is not twisted.
Scalloped surface. Too much camber for the work. Move the iron to a jack, or regrind the smoother's edge closer to straight.
The edge crumbles or chips. The bevel is too thin for the wood, or the micro-bevel has been honed away. Increase the micro-bevel to 30 or 35 degrees, or change the bevel angle on a bevel-up plane.
Honing takes too long. The micro-bevel has grown too wide, or the primary bevel is no longer at the intended angle. Regrind and start with a fresh 0.010 in micro-bevel.
The plane will not stay in the cut. Check clearance first. A 30-degree bevel on a 45-degree frog leaves 15 degrees, and a rounded bevel can reduce that until the heel rubs. Lower the primary angle or use a bevel-up plane.
Frequently Asked Questions
What is the difference between a primary bevel and a micro-bevel?
The primary is the main ground face, usually 25 degrees. The micro-bevel is a narrow strip at the tip, 1 to 2 degrees steeper, honed for sharpness. It saves time because it removes far less metal.
How much camber does a smoothing plane need?
About 0.001 to 0.003 in across the width, just enough to keep the corners from tracking. A smoother with a visible curve is cambered too much and will leave a scalloped surface.
Can I use a cambered iron in a block plane?
Yes, but keep the camber slight. The short sole and fine cut make steering sensitive, and too much camber will round a chamfer or a tenon cheek.
Why does my plane leave ridges after sharpening?
The corners are sharp and the camber is too slight, or the edge is out of square. Ease the corners with a stone and check the edge against a square.
How often should I regrind the primary bevel?
Only when the micro-bevel has widened to about 1/32 in, or when the edge is damaged. Regrinding removes metal, so hone the micro-bevel as long as it stays narrow.
See Also
- Flattening a Hand Plane Sole: When It Matters and When to Leave It Alone
- 2026 Hand-Plane Benchmark Test: Which Bench Planes Leave Glass-Smooth Surfaces Without Tear-Out?
- How a Hand Plane Actually Cuts: Anatomy, Adjustment, and the Right Tuning Order
- How to Tune Up a Hand Plane in 15 Minutes: Sole, Frog, and Blade Setup
- 10 Precision Rulers for Hand-Plane Iron Setup in 2026