Grinding & Sharpening M390
Ceramic belts fresh and sharp while annealed, light cool passes at 120-220 once hard, Trizact-class finishing; diamond/CBN stones at the bench because conventional abrasives stall on its carbides. 17-20 dps edges. Budget ~1.5x the consumables of a mid stainless and price the work in.
M390 earns its benchmark status at the cutting board and collects the bill in the shop: its vanadium and chromium carbides resist your abrasives exactly the way they resist the cardboard. The work is entirely manageable with the right consumables — and slow punishment without them.
On the 2×72
Ceramic belts, full stop — fresh premium ceramics (36-60 grit) hog annealed M390 honestly, while worn belts and cheap aluminum-oxide skate, glaze and heat the bar for nothing. Grind the bulk annealed; post-heat-treat at 60-62 HRC, drop to light passes with sharp 120-220 ceramics and treat every pass as a heat event: this steel holds its temper well, but a thin edge blues as fast as any. Structured-abrasive finishing belts (Trizact class) polish it beautifully for the satin the premium market expects — the progression logic lives in the belt buyer’s guide.
At the Bench
Diamond or CBN stones are the honest answer — conventional stones cut the matrix around M390’s carbides and stall past medium grits, which is where its ‘hard to sharpen’ reputation comes from. A 300/1000 diamond pair plus a strop with diamond emulsion covers the whole life of the edge; owners get that advice with the knife, per the sharpening guide. Edge angles: 17-20 per side suits its toughness class.
The Realistic Budget
Plan roughly half again the belts and bench time of a mid stainless like AEB-L — then price the knife accordingly. M390’s whole business case is that the customer pays for shop effort once and enjoys the edge for months.
Common Mistakes
Worn or aluminum-oxide belts that glaze and burn instead of cutting. Conventional stones past medium grit. Treating a thin 61 HRC edge as heat-tolerant because the bar was. Forgetting to send the diamond-stone advice home with the customer.
Safety
Sharp ceramics remove steel fast – light grip, secure work, and respect for a belt that bites harder than the last steel you ground. Cooling dunks every pass on thin sections; blued M390 means re-heat-treat, not regret.