Alex Garland has spent years teaching freehand sharpening and scientifically testing edges under extreme magnification on his YouTube channel @Outdoors55. His dedication to edge mastery and freehand sharpening led to our first collaboration: the Dual-Grit Diamond Stone Sharpener - OD55 Series.
In this video and blog, Alex breaks down bevels, angles, and knife geometry.
Geometry decides how a knife cuts. The best steel and heat treatment still cut poorly behind the wrong geometry.
The terminology trips up more sharpeners than the stones do. Here is what the words mean, where the angle is measured from, and how to find the one already on your knife.
The Terms That Matter
Most knives carry two bevels. The primary grind sets the overall blade shape. The sharpened bevel, sometimes called the secondary bevel, is the narrow strip at the edge that you actually sharpen.
Scandi grinds are the exception: the primary grind is the sharpened bevel.
The flats are any blade surface parallel to the knife's center line. On a full flat grind that is the small area down by the choil.
Every Angle Starts at the Center Line
Picture the blade in cross-section and draw a line down its center. Every bevel angle, primary or sharpened, is measured from that line.
You can't rest a tool on an imaginary line, so you measure off anything parallel to it. On an RMX DROP POINT, for example, the flat runs down into the choil, and both sit parallel to center.
Angle guides and fixed-angle systems use the same reference. When anyone says a knife is sharpened to 20 degrees, they mean 20 degrees per side, measured from center.
Every angle is measured from the center line.
The Mistake: Inclusive Angle
The inclusive angle is one bevel measured against the other. A 20-degree-per-side edge is a 40-degree inclusive edge.
Mix up the two, sharpen to 40 degrees per side, and the knife will not get sharp. Inclusive numbers also have no fixed reference: both sides could sit at different angles and the figure would never show it.
Chisel grinds prove the point. One side carries a bevel and the other is flat at the center line, so inclusive and per side are the same number. Halve the inclusive figure, as the terminology invites, and you grind the chisel wrong.
Twenty degrees means twenty per side. Always.
When Your Knife Has No Flats
Some blades taper from spine to edge with nothing parallel to center. Zero an angle finder on the bench, set the knife beside it, and read the primary grind. Halve that for degrees per side: a 5-degree reading is 2.5 per side, so a 15-degree guide sharpens that knife at 17.5.
Useful to know, rarely necessary. Freehand bevels end up slightly convex anyway.
Find Your Angle: The Sharpie Test
If you are new to sharpening, match the angle already on the knife. You don't need the number. You need a marker and angle guides, such as the removable guides Alex uses in the video on the Dual Grit Diamond Sharpening Stone and Base – OD55 Series.
1. Color the bevel
Cover the entire sharpened bevel with a permanent marker.
2. Start in the middle
Set the 17-degree guide. From the middle, one pass tells you whether to go up, down, or stay.
3. Make one light pass
Use the 1200-grit side. It removes marker without cutting deep scratches if the angle is off.
4. Read the bevel
Gone at the apex: drop to 15. Gone up at the shoulder: move to 20. Gone in the middle: you're on. Use the closest guide and start sharpening.
Start in the middle. One pass tells you which way to go.
If You Need the Exact Number
Knife makers, professional sharpeners, and anyone replicating a tested geometry across several knives may want the real figure, and the guides only show the guide's angle.
Pull the guides off. The stone surface sits parallel to the center line, so zero the angle finder there. Color the bevel, start low, and raise the knife a few degrees at a time until the marker clears mid-bevel. The example knife lands at 20 to 21 degrees.
Fixed-angle systems need the same check, since clamp depth and blade width shift the true angle. Zero on a flat, adjust until one pass clears the whole bevel, then read the finder on the guide rod.
The guide shows the guide's angle, not the knife's.
The Angle Matters Less Than Holding It
Too obtuse and the edge is never pointy enough to get sharp. Too acute and the apex folds or chips under cutting force. Inside that range, the exact number barely matters for most people.
Holding it through every pass does. That is the job the guides do: they put you in range and steady your motion until the motion is yours.
The OD55 Sharpening System
Designed with Alex. Built for Better Edges.
Throughout the video, Alex uses the Dual Grit Diamond Sharpening Stone and Base – OD55 Series as his freehand sharpener of choice. It pairs a 320/1200 dual-grit diamond stone with an adjustable cast aluminum base and removable 15, 17, and 20 degree angle guides, so the angle you find is the angle you keep.
