A forging should not be finally finished by being Swaged or forged after it has become black hot, because it produces a surface tension that throws the work out of true as the metal is cut away in finishing it.
"Modern Machine-Shop Practice, Volumes I and II"
Joshua Rose
Obviously such swages are employed when the part to be Swaged is less in length than the width of the hammer or of the anvil face.
"Modern Machine-Shop Practice, Volumes I and II"
Joshua Rose
2878, the effect will be to drive the metal towards the centre, and, therefore, to keep it sound at the centre, it being found that if the metal is Swaged much without means being taken to prevent spreading, it "hammers hollow," as it is termed, or in other words, splits at its centre.
"Modern Machine-Shop Practice, Volumes I and II"
Joshua Rose