Bar End Splitting (Fish Mouth) When Drawing Out
When the end of a bar opens up like a pair of fish lips during drawing, the center of the bar has stopped moving while the outside keeps stretching. It is one of the most common forging surprises — and the fix is decisive: cut it off, every time.
Symptom
The end of the bar splits open into two (or four) lips while drawing out u2014 usually preceded by the end face looking cupped or hollow. The split deepens with every additional heat if forging continues.
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.
Quick Checks
Watch the baru2019s end face as you draw u2014 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.
Fixes
Cut or hot-cut the split end off completely, back to sound steel, before continuing u2014 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.
Prevention
Strike hard enough for the stock u2014 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.
When to Stop and Get Help
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.