|Chipping - Course: Technique for manual working of materials. Trainees' handbook of lessons (Institut für Berufliche Entwicklung, 15 p.)|
As a result of the impact of the hammer hitting the head of the chisel, the impact energy of the hammer is transmissed to the cutting edge thus enabling it to do the cutting work.
Figure 15 - Chiselling
The strokes of the hammer are directed mainly by the wrist-joint, because this leads to a good accuracy of aim. Harder strokes must be struck out of the shoulder-joint - do not strike the blows out of the upper arm (little accuracy of aim, rapid tiring).
Look at the cutting edge of the chisel in order to watch its effect.
There is a basic difference in holding the chisel with chipping and parting chiselling.
4.1. Chipping chiselling
The chisel has to be applied in a position inclined towards the surface of the workpiece.
The cutting edge penetrates the material and squeezes it.
As a result, a chip is rolled up from the cutting face and sheared off.
Figure 16 - Position of the chisel when chipping
The angle of inclination is approximately half of the cutting-wedge angle (approx, 30°).
If chips of different thicknesses have to be cut off in order to achieve an even surface, the following has to be observed:
For chips of little thickness hold the chisel steeper (angle of clearance approx. 8°), for thicker chips hold the chisel in a rather flat position (angle of clearance approx. 0°).
- Thin layers of material at narrow surfaces as well as strips of sheet metal are chiselled off by clamping the workpiece into the vice and holding the chisel in an inclined position (angle of incidence approx. 45°).
Figure 17 - Chipping of thin layers by a chisel
- Thicker layers have to be removed by several plies, so that the chips roll off more easily.
- Larger surfaces are treated with the cross-cut chisel first which cuts grooves in them. After this, the webs remaining between these grooves are removed with the help of the flat chisel.
Figure 18 - Chipping of surfaces by a cross-cut chisel
Figure 19 - Chipping of the webs by a flat chisel
How is the chisel applied for the chipping
4.2. Parting chiselling (cutting-off)
The chisel is put vertically on the surface of the workpiece.
Figure 20 - Position of the chisel when cutting off (parting) material
The cutting edge indents the material, squeezes it to both sides and presses it asunder. By this, the material tears in front of the cutting edge the cutting edge is clear. With further penetration, the workpiece tears asunder.
- Thin, flat materials or sheet metal have to be cut off from one side and on a hardened support. The limitting points have to be drilled first.
- Thicker parts have to be indented on all sides and then broken.
Figure 21 - Indenting of a square bar on all sides for parting it
- Long cutting lines have to be prepared by chiselling a guiding slot.
- Curved contours at thicker workpieces (from 4 mm on) have to be prepared by a bore line the scribing is made with the help of a double-point punch.
Figure 22 - Drilling and chiselling out of curved contours
The following conditions apply to this:
D = diameter of the drill
y = width of the double-point punch
x = distance of the bore line to the scribed line
D = y - 0.2 mm
The webs between the bore holes are cut by a flat chisel or cross-cut chisel. With thicker workpieces (from 8 mm on), a cut-out tool is to be used.
How is the chisel applied for the parting
How can curved contours be cut out of thicker