Grinding and Sharpening 8670: Belt Recommendations & Technique
8670 is among the easiest steels on a belt: thin stock means less hogging, clean grinding annealed or hard, and forgiving heat behavior - though thin sections warm fast, so keep passes moving with water close. Convex the edge on the slack belt for choppers. Sharpens on anything abrasive, which is the point of the steel.
8670 might be the most cooperative steel a 2×72 ever meets. It arrives thin, grinds clean, tolerates heat-treat improvisation, and sharpens on anything abrasive. The technique notes here are short because the steel genuinely does not need much — the few that exist are about thin stock and hard use.
Grinding Annealed 8670
Fast and clean with anything sharp — 36–60 grit ceramics for shaping, though on common 0.080–0.125 inch stock a 60 grit start often suffices; there is simply less metal to move. Thin stock flexes: support it against the platen with even pressure or the bevel walks, and mind that thin sections heat quickly even annealed. Drill everything before heat treat as always, and leave the edge a bit thicker than you would on a slicer — these blades usually meet batons.
Grinding Hardened 8670
At 58–60 HRC, 8670 stays polite: no hard carbides tearing at belts, predictable sparks, honest feedback. The usual rules — sharp belts, light pressure, frequent water — protect a temper that in the 400°F range has more margin than razor steels but still is not infinite. Thin stock remains the real heat risk: less mass means faster temperature rise, so pass cadence matters more than pressure. Variable speed earns its keep here; slow the belt for finish passes.
Convex Edges for Hard Use
Most 8670 builds are choppers, and choppers love convex edges. The slack belt section puts one on in minutes: 220 grit, light passes, let the belt’s natural give roll the bevel. A convex edge backs 8670’s bend-not-break toughness with geometry that resists deformation in wood contact — the combination is most of why the steel owns its niche. Full geometry logic in our edge geometry guide.
Sharpening 8670
Nothing exotic: aluminium oxide, ceramic, sandpaper on a mousepad for convex edges, a file in a genuine pinch — 8670’s low wear resistance means everything cuts it, which in the field is exactly the point. It dulls faster than alloyed steels and returns faster too. A few strokes on a pocket stone mid-task beats carrying a powder-steel blade you cannot touch up. See How to Sharpen a Knife for progressions.
Belt Progression
60 grit ceramic start on thin stock (36 for thick), 120–220 refinement, 220 slack-belt convexing for choppers, 400 only if the finish warrants it — working 8670 blades rarely justify mirror work. Spend the belt budget on fresh coarse ceramics; this steel rewards sharpness over grit count. Details: Belt Buyer’s Guide.
Common Mistakes
Letting thin stock flex away from the platen and walking the bevel. Chasing a mirror finish on a working chopper nobody asked for. Grinding a hardened thin blade with a worn belt and cooking the temper through sheer pass count. Skipping the convex edge that the steel’s whole use case is begging for.
Safety
Thin stock develops burrs that slice fingers during handling – deburr edges early and wear gloves off the machine (never near a moving belt). Long choppers put your hands far apart on the work; keep the leading hand clear of the belt line. Carbon dust plus sparks near quench oil is the usual shop fire recipe – separate the stations.