The effects on the workpiece may be varied by different ways of hammering and selecting appropriate hammering faces.
Lengthening means elongating or combined elongating and widening of workpieces.
It is mostly applied to sheet metal strips or strip steel.
When the hammer pane of the engineers hammer hits the entire width of the metal strip, the material is yielding to the front and rear.
Several successive blows lengthen the material - the strip gets longer.
Figure 15 Lengthening with hammer pane
When the hammer face of the engineers hammer hits the metal strip, the material is yielding to all sides.
Several successive blows lengthen and widen the material - the strip gets longer and wider.
Figure 16 Lengthening and widening with hammer face
The blows must be directed from front to rear or rear to front in rapid succession.
Curving means one-sided lengthening of sheet metal strips or strip steel to give a two-dimensional curved shape.
When the hammer pane of the engineers hammer or the faces of the curving hammer obliquely hit one side of the strip, the material is yielding into two directions at this side only. Steady successive hammer blows result in one-sided lengthening of the material, the strip gets longer and curved.
Figure 17 Two-dimensional curving with hammer pane
The blows must be directed as described for lengthening!
Chasing means three-dimensional shaping of thin sheet metal.
Version 1 - flat hammering support
When the hammer face of the chasing hammer hits a sheet metal disk, the material is yielding circularly to all sides.
Steady hammer blows spirally from the centre of the disk outward cause the border to curve upward.
The blows in the middle must be closer than outside!
Figure 18 Chasing on flat hammering support
- The hammer blows must not reach the border!
- The many blows make the metal thinner and harder in the middle - it may easily tear!
- Therefore, sheet steel is to be annealed and gradually cooled down!
- Therefore, sheet copper is to be annealed and quickly cooled down!
Version 2 - hollow hammering support
The metal sheet is put on a steel tube with rounded upper edge and held.
Steady hammer blows with a radiused wooden hammer spirally from the border inward cause the sheet metal to curve downward.
Figure 19 Chasing on hollow hammering support
The hammer blows must reach the centre at the end only!
- The many hammer blows make the metal thinner and harder - it may easily tear!
- Therefore, sheet metal is to be annealed and adequately cooled down!
What makes the difference between lengthening and curving of a sheet metal strip?
How is the blow to be directed when lengthening and curving?
Flanging means bending down of borders of metal sheets obliquely
or perpendicularly to the plane of the sheet. There are two types of
outside flanging and inside flanging.
Principle of outside flanging
The circular sheet is put centrically on a somewhat smaller steel tube. With an engineers hammer, bevelled wooden hammer or aluminium hammer the border projecting outside is bent down by blows hitting obliquely from outside - the border is loosely touching the outside wall of the tube with puckers.
Figure 20 Rough-flanging: bending down of the outside border
Blacksmiths hardies of various shapes, which have to be clamped in a vice, may also be used as hammering support.
with the face of the engineers hammer the puckered border is bulged in on the outside wall of the tube and smoothed.
Figure 21 Finish-flanging: bulging in and smoothing of puckers
Principle of inside flanging
The sheet (1) with the punched hole is inserted in an adequate template (2).
With a bevelled wooden hammer (3).
Figure 22 Rough-flanging: bending down of the inside border
a chasing hammer or curving hammer the border projecting inside is bent down with puckers by blows hitting obliquely.
Blacksmiths hardies of various shapes, the anvil tool or blacksmiths double face sledges may also be used as hammering support.
With the chasing hammer or curving hammer the puckered border is bulged in and smoothed.
Figure 23 Finish-flanging: bulging in and smoothing of puckers
- When flanging very large borders, bending is to be performed step by step!
To avoid heavy puckers, a smooth hardwood counterpiece is used for complete bending down of the border!
Figure 24 Use of hardwood counterpiece for bending down of large borders
- Sheet metal which is flanged to be used as lids or covering cap of containers should be hammered on the relevant container as hammering support to ensure perfect fit!
Which are the working steps when flanging sheet metal borders?