|Chipping - Course: Technique for manual working of materials. Trainees' handbook of lessons (Institut für Berufliche Entwicklung, 15 p.)|
Main tools are chisels of various kinds. They are made of unalloyed tool steel carbon content (0.9 %). The cutting part is hammered, hardened, ground and tempered (HRC 48). The head of the chisel is unhardened, chamfered towards the upper end and rounded.
Chisels are chosen according to the respective task as well as hardness of material of the workpiece:
- Flat chisel
Most common chisel for separating and chipping with straight, broad cutting edge.
- Round chisel
Special chisel for chiselling out big holes or separating curved forms. This chisel has an arched cutting edge.
- Cross-cut chisel
Chisel for chiselling out horizontal grooves or for separating webs in boring lines. The cutting edge is across the width of the chisel, the side surfaces are hollow-ground.
- Shear tool
Chisel for shearing sheet metal. It has a straight, broad cutting edge which is at level with one flank and the shank of the chisel.
- Grooving chisel
Chisel for chiselling out grooves in special workpieces (bearing shells). The cutting edge of the chisel is across the shank, the arched back corresponds to the arched forms.
- Cut-out tool
Chisel for cutting out webs with boring lines and drilled deep-holes.
The two cutting edges are hollow-ground; the flanks are relief-ground in order to avoid jamming.
- Hollow punch
Chisel with circular cutting edge for chiselling out holes in thin or soft materials
Figure 8 - Hollow punch
The following recommended values apply to the selection of chisels according to the hardness of material:
Constitution of the material
30° - 50°
medium hard (steel)
hard (tool steel)
60° - 70°
Figure 9 - Cutting-wedge angle at the chisel
When is the technique of chipping
What material are chisels made
What aspects have to be considered in choosing
When do you use a flat
When do you use a cross-cut
What cutting-wedge angle shall the cutting edges have for
working medium hard
Mostly, hand hammers are used (weight: 400 g); as a general rule:
The hammer should be twice as heavy as the chisel.
For absorbing the beating effect, these should be unhardened: steel plates, steel blocks.
Figure 11 - Anvil with steel support
If the anvil is used, an unhardened intermediate plate is required; when working with the hollow punch, use a wooden support.
Marking-out tables and surface plates must not be used - the chisel edge causes damage that destroys the even surfaces of the plates.
Figure 12 - Collet vice
If possible, use a collet vice for clamping smaller parts and work against a rigid counter-support.
Always beat against the fixed jaw of the vice in order to go easy on the screw.