Blade Grind Geometry on a 2x72 Belt Grinder: Flat, Hollow, Convex, and Scandi Grinds Explained

Our guide to building a 2x72 belt grinder covers the machine itself. This one covers what you actually do with it once it's running: the grind geometry you put on a blade. Flat, hollow, convex, and scandi grinds aren't just cosmetic choices, they change how a blade cuts, how it holds an edge, and how hard it is to sharpen in the field. Getting the geometry right on a belt grinder is a technique problem as much as a tooling problem, and it's easy to ruin a blank by rushing it.

The Four Grinds Compared

GrindCross-section shapeCutting feelEdge durabilityEase of sharpening Flat grindStraight taper from spine to edge, no curveStrong, consistent bite; good general-purpose cuttingGood; thicker behind the edge than a hollow grind at the same edge angleEasy; a flat bevel registers consistently on a stone Hollow grindConcave curve ground in, typically on a large-diameter contact wheelVery thin, acute edge; excellent slicing performanceWeakest of the four for hard use; the thin edge can roll or chip on bone, wood knots, or pryingEasiest to resharpen quickly; the hollow self-jigs against a stone Convex grindOutward curve from spine to edge, no flat bevel at allStrong wedging action; glides through material well on chopping toolsBest of the four; the curve spreads impact force well, which is why axes and heavy choppers often use itHardest; requires a strop, a mousepad-backed sandpaper technique, or practiced freehand work rather than a flat stone Scandi (Scandinavian) grindSingle flat bevel with no secondary edge bevel, running from roughly mid-blade to the edgeExcellent control for push cuts and woodworking (feather sticks, carving)Good for push cuts; not ideal for prying or lateral stressVery easy; the flat bevel itself is the sharpening registration surface, popular with bushcraft knives for exactly this reason

Setting Up the Grinder for Each Grind

GrindPlaten/wheel setupTechnique notes FlatFlat platen, no contact wheelKeep the blade perpendicular to belt travel and use consistent, light passes; a tool rest or jig helps keep the angle identical pass to pass HollowLarge-diameter contact wheel (8" or larger gives a gentler, more versatile hollow than a small wheel)Let the wheel's radius do the work; don't force the blade into the wheel, which digs an uneven hollow ConvexSlack-belt setup (no platen backing, belt allowed to flex) or a dedicated convex wheel attachmentWork in a consistent rocking motion from spine toward edge; convex grinds are the easiest to accidentally make asymmetric side-to-side, so check both faces often ScandiFlat platen, often with a dedicated Scandi/flat-ground jig that holds a fixed angleA jig is strongly recommended here; freehanding a consistent zero-secondary-bevel flat is genuinely difficult even for experienced grinders

Common Mistakes

• Overheating the edge: any of these grinds can draw the temper out of hardened steel if you dwell too long in one spot or grind too aggressively; dip in water frequently and watch for discoloration, the same concern covered in our heat-treating guide.
• Uneven pressure side to side: especially on convex grinds, uneven hand pressure produces a blade that's thicker on one face than the other, which throws off both the cutting feel and the final edge centering.
• Chasing a mirror finish before the geometry is right: get the grind geometry correct at a coarser grit first; polishing a wrong-shaped grind just makes a shiny wrong-shaped grind.
• Skipping a jig on your first scandi or hollow attempts: these two grinds are the least forgiving freehand; a simple shop-built angle jig pays for itself in saved blanks.

Choosing a Grind for the Knife's Job

Match the grind to what the knife is actually for rather than to what looks best: a kitchen slicer benefits from a hollow or flat grind's thin, acute edge; a bushcraft or wood-carving knife wants a scandi grind for its control and field-sharpenability; a chopper or outdoor survival blade that needs to take abuse wants the durability of a convex edge. Many working knife makers settle on a flat grind as their default specifically because it's the most forgiving to execute consistently and performs reasonably well across the widest range of tasks.

Safety Reminder

A 2x72 belt grinder removes material fast enough to be genuinely dangerous to fingers and eyes; keep the tool rest set close to the belt, wear a face shield rated for grinding (not just safety glasses), and never grind without the machine's dust/spark collection running, especially on belts loaded with ferrous grinding dust that can accumulate as a fire risk over time.