Precision machining is a process where material is removed to make a component or part that has a very high tolerance. The tolerance held depends on the machine but more precision CNC machines will not have a problem holding a tight tolerance of 0.0002” or 0.005mm. Precision machining can be classed as milling turning, or jig boring but also includes other types of processes such as laser and water cutters.
Precision machined items are around in everyday items such as car engines, electric motors, or even clocks. Nations such as Switzerland or Germany have a reputation for their capabilities of precision machining with high standards and precision engineering and are still known for this today. Other nations also have lesser of this reputation and of course are able to supply precision made component parts.
Precision machines use a cutter and can be solid cutters such as tungsten carbide, cobalt or High Speed Steel. Watercutters which are very accurate and use extremely high pressure water. Laser cutters use a beam to erode the surface but these units are still very expensive and are not often seen in workshops. Ultrasonic machining centers are used for brittle materials such as ceramics, vibrating the surface and removing small particles. Ceramic materials are often used in inspection equipment for measuring hold tolerances.
A cutting tool which is part of the precision machining process that is the most common tool has one or more sharp cutting edges and is made of a material that is harder than the material that the component is going to be machined from. The cutting edge serves to separate chip from the parent work material. Connected to the cutting edge are the two surfaces of the tool:
- The rake face; and
- The flank.
The rake face which directs the flow of newly formed chips, is located at a certain angle is called the rake angle. It is measured relative to the plane perpendicular to the work surface. The rake angle can be a positive or negative angle. The flank of the tool provides a clearance between the tool and the newly formed work surface, thus keeping the work surface protected from abrasion, which would degrade the finish. This angle between the work surface and the flank surface is called the relief angle.
There are 2 basic types of cutting tools:
- Single point tool; and
- Multiple-cutting-edge tool
A single point tool has just one cutting edge and is used for turning, boring and planing. During machining, the point of the tool penetrates below the work surface of the component. Multiple-cutting-edge tools obviously have more than one cutting edge and usually rotate. Drilling and rotating usually use a rotating multiple-cutting-edge tool. Although the shapes of these tools may vary from a single point tool still many of the elements of the tool geometry are similar.
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