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Chapter 1. Basic Machining and Tips


How to Use a Drill

A drill is one of the most useful and most often used tools. Generally, a drill bit that is used metal work, has two edges with angles of 90 or 120 degrees.

Various drill bits, that have from less than 1 mm diameter to more than 40 mm diameter, are available. However, the chuck of the general drilling machines can use only shaft sizes of less than 13 mm diameter. However, for larger drills and milling machines, drill bits are designed with a "Morse" taper as shown in figure 2.

Fig.1, Drills

Fig.2, Taper Drill

Machines for Milling and Drilling

Figures 3 to 5 respectively pictures a drilling machine, a milling machine and a hand drill. Hand drills are only advised when a high degree of accuracy is not required or it is not practical to mount the work piece in the drilling machine.

Fig.3, Drilling Machine

Fig.4, Milling Machine

Fig.5, Hand Drilling Machine

Wheting of Drill

To achieve accuracy of drilling, the drill bit must be sharp. The bigger drills, such as 6 mm diameter plus, can be wheted (sharpened) using a bench grinder. However, it can be a very difficult process and much practice is needed for the beginner.

Fundamentally, in the wheting process, two edges of the drill have to touch the grinding medium at the same time.

The first step in the whetting proves is to grind the two sides of the drill to an equal angle as shown in figure 7(a). Note, if the angle of both each side is not even as in figures 7 (b) and (c), the drill will not provide a satisfactory cut.

The second step involves grinding to make an "angle of relief" as shown in figure 8(a). Note that if a drill bit does not have an angle of relief, than it is not possible for the drill to drill a hole in the work piece. An example of incorrect angles of relief can be seen in figures 8 (b) and (c).

Fig.6, Edges of a Drill

Fig.7, Angles of Edges

Fig.8, Angle of Relief

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