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6.1. Punch and scriber
The operations are similar with sharpening of punches and scribers.
The left hand guides the tool at the grinding wheel, the right hand moves the tool.
Operation:
Grinding of the taper:
The left forefinger lies between grinding support and tool, the thumb is on the tool.The right hand presses the tool against the wheel in horizontal position at the same time revolving it quickly around its own axis.
Figure 8 - Position of the hands when
grinding the taper of a scriber
Cool at short intervals!
With punches, a forward and backward movement is carried out simultaneously.
Grinding of the point:
The left forefinger lies between grinding support and tool, the thumb is on the tool.The right hand vertically presses it against the wheel in a steeply upward direction revolving it quickly around its own axis.
Grind and cool at short intervals in order to prevent annealing.
Figure 9 - Position of the hands when
grinding the tip (point) of a scriber
Checking
The dimensions are checked by a vernier caliper, the angle by a gauge.
The surface must show a fine finish, the point must be situated right in the centre - on the axis of the tool.
Figure 10 - Dimensions of the centre
punch
Figure 11 - Dimensions of the scriber
6.2. Flat chisel
Grinding the cutting edge:
The left hand holds the chisel so that the forefinger lies close to the grinding support and under the chisel. The right hand vertically presses the chisel against the wheel in a position directed slightly upwards steadily moving it to and fro.Then, the chisel is sharpened from the other side. Cool at short intervals.
Figure 12 - Sharpening of a flat
chisel
Checking:
The angle of the cutting edge is checked by the grinding gauge (60°), the surface and parallelism of the cutting edge is judged by the eye. The cutting edge must be situated in the middle on the axis and be parallel to the outside edges.
Figure 13 - Dimensions of the flat
chisel
Whetting:
The cutting edge is rubbed over the whetstone diagonally and in an inclined way till the burr is removed.
Figure 14 - Whetting of a flat chisel
Sharpening of other types of chisels as well as of scrapers is done in a similar way.
6.3. Drills with standard drill point
Grinding of the principal cutting edges:
The drill is held between the left forefinger and thumb and guided in such a way that the left principal cutting edge comes in a horizontal position in front of the grinding wheel, the drill itself lies horizontally at an angle of incidence of approximately 58° from the left.
Figure 15 - Position of the drill
With slight pressure the drill is led by the right hand upwards from the wheel and, at the same time, slightly pushed to the right - it is lifted above.
This operation is repeated with the other principal cutting edge
Figure 16 - Upward movement of the
drill
Figure 17 - Movement of the drill to
the right
Checking:
After every grinding operation the angle has to be checked by the grinding gauge, the evenness and cleanliness of the surface ground is judged by the eye.
Recommended values:
- Point angle between the principal edges by gauge (118º standard drill point)
- Chisel edge must be exactly in the middle and have an angle of 55°
- Flanks shall taper off at 4 - 6° behind the principal cutting edges
Grinding faults:
- Point angle, angle of clearance, complementary angle of the chisel edge angle too large or too small
- Principal cutting edges (1) different in length (drill out of centre - bore hole too big)
Figure 18 - Consequences of grinding
faults (explanations 1,2,3 in the text)
- Principal cutting edges at unequal (2) angles (shoulder in the bore hole)
- Principal cutting edges different in length and unequal angles of the principal cutting edges (3)
- Incompletely ground principal cutting edges (drill does not cut)
Pointing of the chisel edge:
With drills of a diameter of more than 10 mm the chisel edge is vertically ground at the right edge of the grinding wheel or at the dish wheel in order to reduce the squeezing negative effect of the chisel edge.
Figure 19 - Pointed drill
What characterizes the technique of punch and scriber
sharpening?
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What characterizes the technique of chisel
sharpening?
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How is the operation (movement) with the sharpening of drills to
be carried
out?
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What is understood by 'pointing of the
drill'?
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