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From agent-almanac
Sharpens and maintains knife edges using whetstones, strops, and field-expedient methods. Covers blade assessment, grit progression, burr formation, and edge testing.
How this skill is triggered — by the user, by Claude, or both
Slash command
/agent-almanac:sharpen-knifeThis skill is limited to the following tools:
The summary Claude sees in its skill listing — used to decide when to auto-load this skill
Sharpen and maintain a knife edge using whetstones, strops, and field-expedient methods.
Sharpen and maintain a knife edge using whetstones, strops, and field-expedient methods.
Examine the knife to determine what level of sharpening is needed.
Blade Assessment:
┌─────────────────────┬──────────────────────────────────┬─────────────────────┐
│ Condition │ Signs │ Action Needed │
├─────────────────────┼──────────────────────────────────┼─────────────────────┤
│ Dull (most common) │ Won't catch on fingernail; │ Medium grit → fine │
│ │ slides off tomato skin; │ grit → strop │
│ │ reflects light along edge │ │
├─────────────────────┼──────────────────────────────────┼─────────────────────┤
│ Very dull / abused │ Visible flat spot along edge; │ Coarse grit → │
│ │ tears rather than cuts; │ medium → fine → │
│ │ edge shines under light │ strop │
├─────────────────────┼──────────────────────────────────┼─────────────────────┤
│ Nicked / chipped │ Visible notches in edge; │ Coarse grit to │
│ │ snags on material when drawing │ grind past nicks → │
│ │ across │ reprofile → strop │
├─────────────────────┼──────────────────────────────────┼─────────────────────┤
│ Slightly dull │ Catches on fingernail but not │ Strop only (or a │
│ (maintenance) │ crisply; still cuts paper but │ few passes on fine │
│ │ not cleanly │ grit then strop) │
├─────────────────────┼──────────────────────────────────┼─────────────────────┤
│ Rolled edge │ Edge feels sharp on one side │ Strop firmly on │
│ │ but dull on the other; blade │ both sides; if that │
│ │ curves microscopically │ fails, light passes │
│ │ │ on fine stone │
└─────────────────────┴──────────────────────────────────┴─────────────────────┘
Light Test:
Hold the blade edge-on under a bright light. A sharp edge is invisible —
it has no width. A dull edge reflects a thin line of light where metal
has folded or flattened.
Expected: You know the blade's condition and which grits you need to use.
On failure: If unsure, start with medium grit (1000). You can always refine further, but starting too coarse on a nearly sharp blade removes unnecessary metal.
Choose the right stone for the job.
Abrasive Types:
┌─────────────────────┬─────────────────────────────────┬──────────────────────┐
│ Type │ Characteristics │ Best For │
├─────────────────────┼─────────────────────────────────┼──────────────────────┤
│ Water stones │ Soak 5-15 min before use; │ Home sharpening; │
│ (natural/synthetic) │ fast cutting; wear quickly; │ best feedback and │
│ │ need flattening periodically │ finest edges │
├─────────────────────┼─────────────────────────────────┼──────────────────────┤
│ Diamond plates │ No soaking needed (use water │ Field use; hard │
│ │ as lubricant); very durable; │ steels; flattening │
│ │ aggressive cut │ water stones │
├─────────────────────┼─────────────────────────────────┼──────────────────────┤
│ Ceramic stones/rods │ No soaking; very fine grit; │ Touch-up and │
│ │ hard and slow-wearing │ maintenance; field │
│ │ │ carry │
├─────────────────────┼─────────────────────────────────┼──────────────────────┤
│ Oil stones │ Use honing oil; slower cutting; │ Traditional; │
│ (Arkansas, India) │ very durable; less messy │ workshop use │
├─────────────────────┼─────────────────────────────────┼──────────────────────┤
│ Field stones │ Any smooth, fine-grained stone; │ Wilderness emergency │
│ (improvised) │ river stones, slate, sandstone; │ when no other │
│ │ unpredictable grit │ abrasive available │
└─────────────────────┴─────────────────────────────────┴──────────────────────┘
Grit Progression:
┌──────────────┬────────────────┬──────────────────────────────────┐
│ Grit Range │ Purpose │ When to Use │
├──────────────┼────────────────┼──────────────────────────────────┤
│ 220-400 │ Coarse │ Reprofiling, removing chips, │
│ │ │ establishing a new bevel │
├──────────────┼────────────────┼──────────────────────────────────┤
│ 800-1000 │ Medium │ Standard sharpening of a dull │
│ │ │ blade; the workhorse grit │
├──────────────┼────────────────┼──────────────────────────────────┤
│ 3000-6000 │ Fine │ Refining the edge after medium; │
│ │ │ polishing the bevel │
├──────────────┼────────────────┼──────────────────────────────────┤
│ 8000+ │ Ultra-fine │ Mirror polish; razors; optional │
│ │ │ for most knives │
└──────────────┴────────────────┴──────────────────────────────────┘
Expected: Correct abrasive selected and prepared (soaked, oiled, or wetted as required).
On failure: If no proper stone is available, a ceramic mug bottom (unglazed ring) works as a fine-grit emergency hone. The bottom of a car window works similarly. In the field, a smooth river stone is better than nothing.
The bevel angle determines the edge geometry. Match the existing angle unless reprofiling.
Common Bevel Angles:
┌─────────────────────┬───────────────┬──────────────────────────────┐
│ Knife Type │ Angle (per │ Notes │
│ │ side) │ │
├─────────────────────┼───────────────┼──────────────────────────────┤
│ Bushcraft / fixed │ 20-25° │ Balance of sharpness and │
│ blade │ │ durability for wood, rope, │
│ │ │ and general camp tasks │
├─────────────────────┼───────────────┼──────────────────────────────┤
│ Kitchen knife │ 15-20° │ Thinner for clean food cuts; │
│ │ │ less durable on hard items │
├─────────────────────┼───────────────┼──────────────────────────────┤
│ Japanese kitchen │ 10-15° │ Very acute; exceptional │
│ │ │ sharpness; fragile on bone │
├─────────────────────┼───────────────┼──────────────────────────────┤
│ Machete / chopper │ 25-30° │ Thick for impact resistance │
├─────────────────────┼───────────────┼──────────────────────────────┤
│ Folding knife (EDC) │ 20° │ General purpose │
├─────────────────────┼───────────────┼──────────────────────────────┤
│ Hori-hori / garden │ 15-20° │ Similar to kitchen; for soil │
│ blade │ │ and root cutting │
└─────────────────────┴───────────────┴──────────────────────────────┘
Finding the Angle:
1. Lay the blade flat on the stone (0°)
2. Slowly raise the spine until the bevel sits flush on the stone
3. The point where the entire bevel contacts the stone is the correct angle
4. Marker trick: color the bevel with a Sharpie, make one stroke on the stone.
- Ink removed from the whole bevel = correct angle
- Ink removed only at the edge = angle too high
- Ink removed only at the shoulder = angle too low
Coin Stack Reference (for consistent angle):
- 1 coin under spine ≈ 12-15° (thin kitchen knives)
- 2 coins under spine ≈ 17-20° (general purpose)
- 3 coins under spine ≈ 22-25° (bushcraft / heavy use)
(Varies with blade width — wider blades need more coins for the same angle)
Expected: You can hold the knife at a consistent angle that matches the existing bevel.
On failure: If you cannot maintain a consistent angle freehand, use a sharpening guide or clamp system. Inconsistent angle is the most common cause of poor sharpening results. Practice on a cheap knife before working on a valued blade.
Work through the grits from coarsest needed to finest.
Sharpening Technique:
SETUP:
1. Place stone on a stable, non-slip surface (wet towel underneath)
2. Ensure the stone is fully saturated (water stones) or oiled (oil stones)
3. Position yourself so you can make smooth, controlled strokes
STROKE METHOD (per side):
1. Place the blade on the stone at the correct angle
2. Push the edge forward along the stone as if slicing a thin layer off
the surface — from heel to tip in a sweeping arc
3. Maintain consistent pressure and angle throughout the stroke
4. Light to moderate pressure — let the abrasive do the work
5. 5-10 strokes per side, then alternate
ALTERNATING PATTERN:
- 5-10 strokes on side A → 5-10 strokes on side B → repeat
- As you approach a sharp edge, reduce to 3 strokes per side,
then 1 stroke per side (alternating single strokes)
CHECKING FOR A BURR:
- After sufficient strokes on one side, a thin wire edge (burr)
forms on the opposite side
- Feel for it: drag your thumb ACROSS the edge (never along it)
from the spine toward the edge — the burr catches slightly
on the side opposite to the one you were sharpening
- A burr means you have reached the apex — move to the other side
- Once both sides have raised and removed the burr, move to the
next finer grit
PROGRESSION:
Coarse (if needed) → raise burr on both sides → move to medium
Medium → raise burr on both sides → move to fine
Fine → light alternating strokes → strop
Expected: After the finest stone, the blade catches firmly on a fingernail and slices paper cleanly (some drag acceptable before stropping).
On failure: If you cannot raise a burr after 20+ strokes, check your angle — you may be too steep (grinding above the edge) or too shallow (grinding the flat of the blade). Use the marker trick again. If the stone is glazed (loaded with metal particles), rinse it and rub with a nagura stone or flattening plate.
Stropping removes the final burr and aligns the edge to razor sharpness.
Stropping Protocol:
1. Use a leather strop, smooth cardboard, or bare softwood (palm side
of a leather belt works in the field)
2. Apply stropping compound if available (chromium oxide / green compound,
or fine polishing paste)
3. Lay the blade flat at the sharpening angle
4. Draw the blade SPINE-FIRST (opposite direction to sharpening —
you are dragging the edge backward, not pushing it forward)
5. Light pressure only — less than sharpening
6. Alternate sides: 5 strokes per side → 3 → 1 → 1 → 1
7. Total: 20-30 strokes alternating
⚠️ CRITICAL: Strop spine-first (pull the edge backward).
Pushing edge-first into a strop cuts the leather and
dulls the blade.
Field Strop Alternatives:
- Smooth side of a leather belt (hold taut)
- Cardboard or newspaper laid flat
- Palm of your hand (careful! very light pressure, spine-first only)
- Smooth driftwood or the flat of a dry log
Expected: The blade pops arm hair, slices phone-book-thin paper cleanly, or glides through a tomato under its own weight.
On failure: If the edge feels sharp but catches or drags, there may be a remaining burr on one side. Do 5 more alternating single strokes on the fine stone, then re-strop. If the edge is still inconsistent, you may have a slightly different angle on one side — mark with Sharpie and correct.
Use progressive tests to gauge the edge quality.
Sharpness Tests (from easiest to most demanding):
1. FINGERNAIL TEST (basic):
Lightly draw the edge across a fingernail at 45°.
Sharp: catches and digs in immediately
Dull: slides across without catching
2. PAPER TEST (good):
Hold a sheet of printer paper by one edge and slice downward.
Sharp: cuts cleanly with no tearing
Acceptable: cuts with slight drag
Dull: tears, folds, or won't start a cut
3. TOMATO TEST (kitchen standard):
Place a ripe tomato on a cutting board.
Sharp: the weight of the blade alone starts the cut
Dull: requires downward pressure to break the skin
4. ARM HAIR TEST (very sharp):
Lightly draw the blade across arm hair without touching skin.
Sharp: hair pops cleanly
Not quite: hair bends or pushes aside
5. HANGING HAIR TEST (razor sharp):
Hold a single hair and bring the blade to it.
Razor: cuts the hair with minimal pressure
This level is unnecessary for most bushcraft/garden use.
Sharpness Standards by Use:
- Bushcraft / camp knife: pass paper test cleanly → good to go
- Kitchen knife: pass tomato test → good to go
- Carving knife: pass arm hair test → ideal
- Garden blade (hori-hori): pass paper test → sufficient
Expected: The blade passes the sharpness test appropriate for its intended use.
On failure: If the blade passes fingernail but fails paper, it needs more time on the fine stone and more stropping. If it fails fingernail entirely, go back to medium grit and re-sharpen from Step 4.
When proper stones are not available.
Field Expedient Sharpening:
RIVER STONES:
1. Find a smooth, flat, fine-grained stone (slate, granite, basalt)
2. Wet the surface
3. Use the same technique as Step 4 — angle, stroke, alternate
4. Won't produce a polished edge but will restore cutting ability
5. Look for stones with a slightly gritty feel — glassy smooth
stones won't cut fast enough
CERAMIC:
- Bottom of a ceramic mug (unglazed ring) serves as a fine hone
- Excellent for maintenance touch-ups in camp
CAR WINDOW EDGE:
- The edge of a car window (rolled down slightly) is fine-grit ceramic
- 5-10 strokes per side for a quick field touch-up
SANDPAPER ON FLAT SURFACE:
- If you have sandpaper (any grit), place it on a flat log or rock
- Sharpen as you would on a stone
- Works surprisingly well
LEATHER BELT STROP:
- Always available in the field if wearing a belt
- Hold taut between hand and fixed point
- Strop spine-first after any field sharpening
Minimum Field Sharpening Kit (recommended carry):
- Small diamond plate (credit-card size) or ceramic rod
- Leather strop strip (10cm x 3cm, fits in sheath)
These two items weigh almost nothing and handle all field needs.
Expected: Blade restored to functional sharpness sufficient for camp tasks.
On failure: If no suitable abrasive can be found, a flat piece of hardwood with fine sand rubbed into the grain can serve as a crude sharpening surface. Prioritize getting the blade functional rather than perfect.
Prevention is easier than restoration.
Edge Maintenance Habits:
1. Strop before each use — 10 strokes per side on leather or cardboard
(this alone can keep a knife sharp for weeks between stone sessions)
2. Cut on wood, not stone, glass, ceramic, or metal surfaces
3. Never pry, twist, or use the edge as a screwdriver
4. Clean and dry the blade after use — moisture causes corrosion,
and corrosion eats the fine edge
5. Store knives in sheaths, on magnetic strips, or in blade guards —
never loose in a drawer where edges contact other metal
6. Carbon steel: oil the blade after cleaning (camellia oil, mineral oil)
7. Stainless steel: less maintenance, but still benefits from drying
and occasional oiling
Sharpening Frequency:
┌───────────────────┬────────────────────────────────────────┐
│ Use Pattern │ Recommended Frequency │
├───────────────────┼────────────────────────────────────────┤
│ Daily kitchen use │ Strop daily; stone weekly │
│ Weekend bushcraft │ Strop before each trip; stone monthly │
│ Occasional garden │ Strop before use; stone seasonally │
│ Heavy field use │ Strop daily; stone every 2-3 days │
└───────────────────┴────────────────────────────────────────┘
Expected: A maintenance routine that keeps the blade sharp between full sharpening sessions.
On failure: If you find yourself needing full coarse-to-fine sharpening frequently, either the steel is too soft for the task (consider a harder knife) or the blade is being damaged by misuse (cutting on hard surfaces, lateral torque, corrosion).
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