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According to the mode of action of the bits, forces are required for the rotary motion of the bit brace and for the feed motion in the in the direction of the bore hole depth.
Figure 9 Boring forces
1 feed motion, 2 working motion
The magnitude of the required force depends on
- the strength of the material to be cut,
- the diameter of the bit,
- the cutting edge geometry of the bit,
- the desired quality of cutting and
- the feed rate.
All bits with brad point and pre-cutters are a potential source of accidents unless they are properly handled. Therefore, specific rules of labour safety are to be defined and observed.
Bits must not be left lying around but be stored in proper holders! Bits must not be used for scribe-marking or similar purposes!
Boring is to be carried out as follows:
- The part to be bored is to be clamped, if possible, in order to prevent it from being moved by the rotary motion of the bit.- If it is not possible to clamp the workpiece, assistance by a second worker is required.
- The face to be bored must be horizontal to permit the bit to cut vertically from top to bottom. In that case less feed force is required.
- Before boring the scribe-marked centre of the hole (pencil or scriber marking) should be punched to prevent the bit from running off centre.
- During boring the position of the bit with the boring appliance is to be constantly checked from all sides to make sure that the hole is produced in the correct position.
- A boring fixture should be used, if possible, to facilitate keeping up the correct position.
- When using bits with brad points without draw-in thread, the feed rate is to be selected so as to achieve favourable chip thicknesses.
- When boring through holes it is to be made sure that no wood fibres are torn off at the bottom side of the workpiece. This can be prevented in two different ways:
. Clamp a piece of waste wood under the bottom side and bore through into such piece of wood.. Check during boring whether the brad point has reached the bottom side. If that is the case, stop boring, turn the workpiece over and complete boring from the second side.
Why is it necessary to constantly check the position of the boring tool during boring?
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