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

Troubleshooting

Bar End Splitting (Fish Mouth) When Drawing Out

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.
Gray cold forged bar end split into two curled lips with a short crack running inward, resting on a dark steel block.

The flow

Work it in this order

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

  1. Likely causes

    Blows too light for the stock size: light blows only move the surface, so the outside lengthens while the center lags, and the end face hollows until it tears. Contributing factors: wrong hammer angle, drawing with flats only on square stock, and working the very end of the bar while it is coolest.

  2. Quick checks

    Watch the baru2019s end face as you draw — cupping inward is the warning before the split. If your blows leave shallow surface prints on heavy stock instead of visibly moving the section, you are in fish-mouth territory.

Cooled square forged bar held by tongs on an anvil, its end face shallowly cupped inward with the rim still intact.

  1. Fixes

    Cut or hot-cut the split end off completely, back to sound steel, before continuing — the split never forge-welds itself closed, and forging over it folds the tear inside the bar as a cold shut. Losing an inch of bar now beats losing the blade later.

Short fish-mouth offcut with a torn split end lying on a dark bench beside a flat, freshly sawn bar end held in wooden blocks

  1. Prevention

    Strike hard enough for the stock — heavy sections need authoritative blows or a bigger heat (see hammer technique). Crown or chamfer bar ends before drawing so the center leads. Work at full forging heat, and leave the very end slightly proud, trimming it at the finish rather than forging it thin.

Gloved hands file the corner of a steel bar end held upright between leather-padded vise jaws in a dim shop.

  1. When to stop

    If the split has propagated into the length you meant to be blade, keep cutting back to fully sound steel no matter how much bar it costs. A trace of fish mouth left in the bar is a delamination waiting inside your finished blade.

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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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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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