Milling and Turning

Removing material by the process of a machine’s use of rotary cutters is known as milling. This is achieved when the cutter is advanced into the work piece; and also by varying direction on an axis or several axes, varying pressure and by varying the speed of the cutter head.

A wide range of machines and operations are covered under the description of milling. This ranges from individual small parts right to very large and gang heavy-duty milling operations. Milling will get a mention amongst most commonly applied processes with regards to the machining of common parts to achieve precise tolerance. You can read more from this article.

On the other hand, turning is a process in machining where cutting tools, traditionally non-rotating tool bits, defines helix tool paths through linear movements as the work piece is kept rotating. Turning is usually used as the descriptive term for the external surfaces generated as a result of the cutting action.

It is to be noted that when this same cutting is utilized in internal surfaces, like different sorts of holes, it is known as boring. You can now understand how that phrase, turning and boring, became a term for a larger class of processes called lathing.

Milling Defined Machine Tooling

Machine tools of a wide variety can be used for milling. A mill, or milling machine, was the original machine tools family. When in the 1960s the invention of computer numerical control came unto the scene, these milling machines transformed to machining centers.

These centers are augmented milling machines; augmented by tool carousels or magazines, coolant systems, CNC capability, enclosures and automatic change of tools. These machining centers later became classified as vertical (VMCs) or horizontal (HMCs) centers. Occasionally using mills in turning operations and for lathes’ live tooling, were what saw to milling being integrated into the turning world.

As already mentioned, milling is a process of cutting that takes out material from a work piece’s surface through the work of the milling cutter. This milling cutter is a tool that rotates and comes with several cutting points. It differs from drilling, a case in which the tool is pressed forward along its axes of rotation. In milling, the cutter moves perpendicularly to the axis, therefore allowing cutting to happen on the cutter’s circumference.

Tooling by Whittling

As this cutter penetrates the piece in a repeated manner, its cutting edges penetrates the material. With each repeated penetration, swarf or chips come off the material with every pass from the tools cutting edge of teeth or flutes. This actually may be seen as deformation of the material, as tiny parts of the material are whittled off the work piece in chunks that eventually forms chips. This formation of chips makes metal slicing mechanically different from same slicing done on other softer materials.

The process of milling sees to the removal of material by making several separate little cuts. To accomplish this, a cutter with several teeth is employed. This cutter then spins at very high speeds, or the material is pressed slowly towards the cutter.

Some processes use the three applications of cutter having several teeth, high-speed spinning cutter and slowly pressing the material on cutter, to bring about milling. The pace of the work piece’s progress past the cutter is known as the feed rate or just feed. This is measured by the material’s length for every full revolution the cutter makes. Feeds and speeds are adjustable, and are adjusted to conform to quite a mix of variables.

Turning, the Other End of Machining

There are two ways that turning can be achieved; manually or automated. When done manually, this is in the mode of lathe and demands constant operator supervision. When automated, the need for constant supervision is eliminated. CNC (Computer Numerical Control) is the most used form of automated turning. In turning, the cutting tool moves through a number of axes, usually not exceeding three, while the work piece is kept in a relatively rigid position. This produces quite precise depths and diameters.

A lathe is what is usually used in the turning process. This is considered amongst machine tools as probably the oldest and is known to come in different types. These are seen in taper turning, straight turning and external grooving or profiling. With these, various sorts of shapes like conical, straight, grooved or curved shapes have been produced in work pieces. Lathes in the past were used to produce very complicated geometric figures, even platonic solids. However since the advent of CNC, it is quite unusual to see turning processes done manually.

Generally, cutting employs uncomplicated single-spot cutting tools, where each set of work piece has a maximum set of angles developed as time progressed. The tools’ movement axes could be straight literally or they may traverse a series of curved paths or angles. However their movement goes –straight, curved or angled – these movements are essentially of a linear nature in a non-mathematical sense.

Between Milling and Turning

So, how do you know if you should be using a milling or turning process to manufacture a part you want to make? You surely would want to know the process that would be most efficient for your work. In another way this is actually like asking about the difference between the two machining options.

Now in turning, cutting tools that are stationary are used to remove materials from a part mounted on rotary chuck. Given this, it is much easier to machine a part having symmetry by its center axis. Typically, turned parts when compared to milled parts are both cheaper and more quickly produced. This will be the case at any prototype machine shop – Zero Hour Parts or other reputable companies.

However, although milling is the more popular process of machining, accessing the tool can pose a major impediment in the design. This is because you have just three axes of X, Y and Z to work with, making the reach of certain areas quite impossible. In a situation where the part needs to be rotated just once, this wouldn’t be a problem. However, in the event of a need for multiple rotations, a problem that eventually increases machining hours and labor cost arises.

In Conclusion

The basic difference between your turning operation and its milling counterpart is that in turning, the part you intend to have machined rotates. On the other hand, in milling it is the tools that rotate while your machined part is kept stationary. You will find turning very suitable for cylindrical pieces, where it is used in the reduction of a cylinder’s diameter. The implication is that more complex and detailed parts that are meant for higher volumes production, will do better using a turning machine.


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