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What are CNC Milling and CNC Turning?

CNC Milling / CNC Turning

What is CNC Milling?

CNC stands for Computer Numerical Control. CNC milling is a computer controlled milling process that is very effective on cutting products. A CNC milling machine makes it possible for anyone to produce finely milled metal products for use in a variety of applications.

Multi-axis milling is a process where part of the workpiece is removed by using a rotating tool. This tool is moved in different directions to achieve a desired shape. A variety of shapes are available as cutting tools, such as squares or triangles and they can be rounded or angled. 2D and 3D shapes are also possible. The result is a visible pattern in the workpiece.

CNC milling machines allow users to create intricate patterns in metal materials like steel and aluminum. They are also useful for machining delicate parts such as pistons, valves, and other engine components. Because they are controlled by a computer, CNC milling machines offer a higher degree of accuracy than can be achieved with hand operated mills or lathes. The concept of using a mill to hone metal has been around for more than a century. Milling machines have taken this process a step farther by making it possible to machine the same type of piece over and over again to precise specifications.

They are used to finish off metal pieces ranging from cylinder heads for lawnmower engines to turbine blades for jet engines. A CNC machine can reproduce the same level of accuracy over a production run of several hundred pieces (with regular cutting tool sharpening), which makes it an invaluable tool for anyone producing large numbers of parts for a variety of applications. It can be used for smaller tasks as well.

What is CNC Turning?

Turning is the machining operation that produces cylindrical parts. In its basic form, it can be defined as the machining of an external surface:

Taper turning is practically the same, except that the cutter path is at an angle to the work axis. Similarly, in contour turning, the distance of the cutter from the work axis is varied to produce the desired shape.

Even though a single-point tool is specified, this does not exclude multiple-tool setups, which are often employed in turning. In such setups, each tool operates independently as a single-point cutter.

Adjustable cutting factors in turning

The three primary factors in any basic turning operation are speed, feed, and depth of cut. Other factors such as kind of material and type of tool have a large influence, of course, but these three are the ones the operator can change by adjusting the controls, right at the machine.

Speed, always refers to the spindle and the workpiece. When it is stated in revolutions per minute (rpm) it tells their rotating speed. But the important figure for a particular turning operation is the surface speed, or the speed at which the workpiece material is moving past the cutting tool. It is simply the product of the rotating speed times the circumference (in feet) of the workpiece before the cut is started. It is expressed in surface feet per minute (sfpm), and it refers only to the workpiece. Every different diameter on a workpiece will have a different cutting speed, even though the rotating speed remains the same.

Feed, always refers to the cutting tool, and it is the rate at which the tool advances along its cutting path. On most power-fed lathes, the feed rate is directly related to the spindle speed and is expressed in inches (of tool advance) per revolution (of the spindle), or ipr. The figure, by the way, is usually much less than an inch and is shown as decimal amount.

Depth of Cut is practically self-explanatory. It is the thickness of the layer being removed from the workpiece or the distance from the uncut surface of the work to the cut surface, expressed in inches. It is important to note, though, that the diameter of the workpiece is reduced by two times the depth of cut because this layer is being removed from both sides of the work.

This technical information has been contributed by
Peko Precision Products Inc.

Click on Company Name for a Detailed Profile

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