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Nebula dual-axis tracking assembly: star knob, spring and idler wheel, close-up, on black with a purple glow

Troubleshooting

Cold Shuts and Laps in a Forged Blade

Work back from what it is doing to what caused it, then to the fix that addresses the cause. Nothing here needs a sign-up.

Forging and bladesmithing in a working knife shop
If a symptom appears mid-job, put the work down and check it before continuing.
Rough forged knife blank on a brown leather pad with a short dark lap seam in the hammer-textured flat near the tang.

The flow

Work it in this order

Causes first, then the quick checks, the fix, prevention and the stop-work point.

  1. Likely causes

    Steel folded over itself during forging: hammering below forging heat (dull red or cooler), sharp bar corners folding over during drawing, over-thinning one facet before rotating the bar, or scale hammered into the surface between heats. The fold traps oxide, so the two surfaces touch but never weld.

  2. Quick checks

    Grind a shallow window across the line: a scratch disappears evenly, a cold shut stays as a defined seam. Check the ends of the line — rounded, folding ends suggest a shut; sharp tips running from the edge or a hole suggest a quench crack instead. An etch (even vinegar) makes the seam jump out.

Forged knife blank on a dark pad with a ground bright window crossed by a thin dark seam that stays visible.

  1. Fixes

    Shallow shut with thickness to spare: grind past it completely and confirm with an etch — on a 2x72 this is a two-minute diagnosis. Deep shut with forging stock left: cut or grind back to sound steel and re-forge. A shut that reaches the final edge or bevel envelope is not fixable — see below.

Clean square-cut forging bar beside a tray holding a short offcut with a folded seam; hacksaw idle behind

  1. Prevention

    Stop hammering at dull red — cold steel folds instead of flowing. Keep bar corners lightly radiused while drawing. Rotate evenly instead of over-thinning one side (the same discipline as bevel forging). Wire-brush scale between heats, and build hammer accuracy so blows land flat, not on edges.

Gloved hand brushing loose scale off a glowing orange bar lying on an anvil, with flakes of scale on the face.

  1. When to stop

    If the seam intersects the final edge or survives into the finished blade envelope, scrap the blade. A cold shut is a stress riser: hardened and put to work, it is where the blade will crack. Never harden or sell a blade with a known shut in the working zone — steel is cheaper than reputation.

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Guides that cover the cause

The long-form version of the fix above, written from the same bench.

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Same bench

When the machine is the cause

Flex, a soft platen or a tracking knob that will not hold can show up as a bad grind. I machine the parts, hand-assemble, track and test each Torus grinder in Sterling, Illinois.

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    Torus 2×72 Classic Aluminum Belt Grinder

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