Knife Forging

Part of Metalworking

Step-by-step knife making from raw steel, from bar stock to finished blade.

Why This Matters

The knife is the most essential and versatile tool in any survival or rebuilding scenario. It processes food, shapes wood, cuts cordage, defends its owner, and performs hundreds of daily tasks that no other single tool can match. A well-made knife lasts years of hard use. A poorly made one fails in days — the edge rolls, the blade bends, the handle loosens, or the steel shatters.

Knife forging is also the foundational project for any aspiring blacksmith. It teaches every core skill: heating, hammering, drawing out, shaping, heat treatment, and finishing. A community member who can forge a good knife can eventually forge anything — axes, chisels, plowshares, surgical instruments.

The process described here starts from a bar of carbon steel (wrought or bloomery iron that has been carburized, or scavenged high-carbon steel like vehicle springs, files, or saw blades) and ends with a finished, sharp, handle-mounted knife ready for daily use.

Selecting Steel

Not all steel makes a good knife. You need medium-to-high carbon steel (0.50–1.0% carbon) for a blade that will harden and hold an edge.

Good scavenged sources:

Source	Carbon Content	Notes
Leaf/coil springs	0.60–0.80%	Excellent knife steel, widely available
Old files	0.90–1.20%	Very hard, good for small blades
Circular saw blades	0.70–0.85%	Good, but thin stock
Plow discs	0.50–0.70%	Good for larger blades
Ball bearings	0.95–1.10%	Excellent but hard to forge
Rebar	0.20–0.40%	Too low carbon for edges — avoid
Mild steel plate	0.10–0.20%	Will not harden — do not use for blades

From bloomery iron: If working from smelted iron, you need to carburize it first. Pack iron bars in charcoal inside a sealed clay container and heat to bright red for 6–12 hours. This diffuses carbon into the surface, converting iron to steel. See Steel Production for detailed methods.

The Spark Test

Before investing hours of forging, confirm your steel’s carbon content with a spark test on a grinding stone. Exploding white sparks at the tips indicate carbon — the more bursts, the higher the carbon. Smooth orange trails with no bursts mean low carbon steel that will not harden.

Forging the Blade

Tools Required

• Forge (coal, charcoal, or gas)
• Anvil (or a heavy, flat piece of steel/iron — a section of railroad rail works)
• Hammer (1–1.5 kg cross-peen or ball-peen)
• Tongs (flat-jaw for flat stock, v-jaw for round stock)
• Water bucket (for cooling tongs and hands, not for quenching the blade)
• Quenching oil (vegetable oil, motor oil — any oil)
• Wire brush

Step 1: Establish the Profile

1. Cut your stock to roughly 25–30 cm for a standard utility knife. Use a hot cut (a chisel struck into glowing-hot steel on the anvil) or a hacksaw on cold steel.

2. Heat to forging temperature — bright orange to yellow-orange (900–1,050°C). The steel should be easy to move under the hammer. If you have to hit hard, it is too cold.

3. Draw out the blade. Start 3–5 cm from one end (this will become the tang). Hammer the working end thinner and longer, working from the tang-end toward the tip. Flip the piece regularly to keep both sides even.

4. Form the point. Angle your hammer blows to draw the tip to a point. Work both sides equally. The point should be centered on the blade’s thickness, not offset to one side.

5. Form the tang. Heat the handle end and draw it out thinner and narrower than the blade. For a full tang (strongest), flatten it to blade width but half blade thickness. For a hidden tang (simpler handle attachment), draw it to a square or round cross-section about 8–10 mm.

Do Not Forge Cold

Never hammer steel below dull red heat (about 600°C). Cold forging introduces micro-cracks that become catastrophic failures during heat treatment or use. If the steel loses color, put it back in the forge.

Step 2: Refine the Shape

1. Straighten the blade. Lay it flat on the anvil and tap down any curves or twists. Check straightness by sighting down the spine from the tang end.

2. Establish the bevels. Tilt the blade on the anvil edge and hammer the edge side thinner, working from spine toward edge. Do NOT forge the edge to final thinness — leave it about 1.5–2 mm thick at the edge. Final edge geometry is achieved by grinding after heat treatment.

3. Normalize. Heat the blade to critical temperature (non-magnetic — use the magnet test) and let it cool in still air. Repeat 2–3 times. This refines the grain structure and relieves forging stresses, producing a blade that heat-treats predictably.

Step 3: Heat Treatment

This is the step that makes or breaks the knife. See Heat Treatment for full theory.

1. Heat evenly to critical temperature. The entire blade should be uniformly cherry-red to bright red. Use the magnet test — when the blade stops attracting the magnet, it is ready.

2. Quench in oil. Plunge the blade edge-first into a deep container of oil. Move it gently in a figure-eight motion. Keep it submerged for 10–15 seconds (until it stops sizzling).

3. Test hardness. Try to cut the blade with a file. If the file skates off without biting, hardening was successful. If the file bites, the steel did not reach critical temperature or has insufficient carbon — reheat and try again.

4. Temper immediately. The blade is now glass-hard and will shatter if dropped. Clean a section with sandpaper to bare metal. Heat gently (in a forge, over coals, or in a kitchen oven at 220–240°C) until the polished section turns straw-yellow. Quench in oil to stop the process.

Oven Tempering

If you have any kind of oven with temperature control, use it for tempering. Set to 220°C for a utility knife or 200°C for a razor-sharp fillet knife. Hold at temperature for 1 hour, let cool in the oven. This produces far more consistent results than color-judging over a forge.

Step 4: Grinding and Finishing

1. Grind the bevels. Using a coarse stone (sandstone, granite, or manufactured grinding wheel), establish the final edge geometry. A convex grind (slight curve from spine to edge) is strongest for a general-purpose knife. A flat grind (straight taper) is sharper but more fragile.

2. Work through grits. Progress from coarse grinding stone to finer stones. Each stage removes the scratches of the previous one:

   • Coarse (60–100 grit equivalent): shape the bevel
   • Medium (200–400 grit): refine the bevel
   • Fine (600–1000 grit): pre-sharpening polish

3. Sharpen the edge. Use your finest stone with light, consistent strokes at a fixed angle (15–20° per side for a utility knife). Alternate sides every few strokes. Stop when you can shave hair from your arm.

Step 5: Handle Construction

Hidden tang (simplest method):

1. Select a handle block — hardwood (oak, maple, walnut, hickory) or antler
2. Drill a hole matching the tang diameter and length
3. Heat the tang to dull red and burn it into the handle for a precise fit
4. Apply epoxy, pine pitch, or hide glue to the tang
5. Press the handle on and let cure
6. Add a pin through the handle and tang for security

Full tang with scales:

1. Cut two handle slabs (scales) to match the tang shape
2. Drill matching holes through both scales and tang — minimum two pins
3. Rivet with brass, copper, or steel pins
4. Shape and sand the handle to a comfortable grip
5. Oil the wood with linseed oil or beeswax

Guard and Bolster

A simple guard (a piece of brass or steel with a slot filed to fit the tang, positioned between blade and handle) prevents the hand from sliding onto the edge during hard use. For a utility knife, this is not decorative — it is a safety feature.

Testing the Finished Knife

Before trusting your life to a forged knife, test it:

1. Flex test: Clamp the handle in a vise and flex the blade 15° to each side. It should spring back straight without taking a set. If it bends permanently, it is too soft. If it snaps, it is too hard — re-temper at a higher temperature.

2. Cutting test: Slice through thick rope or cardboard for 50 strokes. Examine the edge under magnification (or by feel). Minimal edge rolling indicates proper hardness.

3. Chopping test: For a utility/camp knife, chop into a softwood block 20 times. The edge should show no chipping or deformation.

4. Batoning test: Place the blade on a piece of wood and strike the spine with a baton to split the wood. The blade must survive this without cracking. If it chips or cracks at the edge, temper at a slightly higher temperature.

Common Forging Mistakes

Mistake	Result	Fix
Forging too cold	Micro-cracks, blade failure	Return to forge when color fades
Uneven bevels	Blade curves when hardened	Grind to correct before heat treat
Quenching too fast (water)	Cracks, especially at transitions	Use oil for all knife quenching
Skipping normalization	Unpredictable hardening	Always normalize 2–3 times
Tang too thin	Handle loosens, snaps under load	Tang should be at least 6 mm thick
Edge too thin before hardening	Warps or cracks during quench	Leave 1.5–2 mm at edge before quench