Turning Operation and Turning Machines – Types and Terms

We use material removal processes or machining processes extensively in the manufacturing of metal parts. So, turning operations are one of the machining operations that we use extensively in the production of different parts. Here we explain; 

  • Turning and definitions of related terms about turning operations, 
  • General types of turning operations and explanations of them, 
  • Engine lathe configurations in turning operations, 
  • Types of turning lathes turning operations, 

What is Turning? 

Turning operation.
Image Source: Wikimedia.

Firstly, turning is a specific machining process in which material removal takes place by a single-point machine tool. The workpiece is rotated along its axis and the feed motion of the machine tool is performed parallel to the axis of rotation of the workpiece. 

Furthermore, like the other machining operations, they form chips. So, the most used type of machining is the radius reduction of the cylindrical parts. There are strict calculations for the turning operation design of the parts. You can use the calculators related to turning operation from the given link. 

We carry out the turning operations in engine lathes where the workpiece rotates and the feed motion of the cutting tool take place along the axis. 

What is the Primary Motion in Turning Operations?

In machining operations, primary motions are the motions that machines carry out by the workpieces or machine tools to perform chip removal or material removal. So, in turning operations, the rotation of the workpiece carry out the primary motion around its axis. 

What is the Feed Motion in Turning Operations? 

Also in machining operations, feed motions are the secondary motions that complete the total machining operation. The feed motion in a turning operation is the motion of the machine tool which is generally parallel to the axis of rotation of the workpiece. Also, there are other types of turning operations where feed motion is perpendicular to the axis of rotation.

What is Lathe? How the Lathes are Working? 

Turning machine parts.
General elements of a engine lathe(Image Source: Mechtalk.info).

The general construction of engine lathes like above. You can see the general elements of engine lathes that have different kinds of duties. 

  • Headstock: We mount the the workpiece to the spindle to turn the work part around the axis of the spindle to obtain the primary motion of the engine lathe. The headstock is the element of a lathe machine we attach the spindle. 
  • Tailstock: Tailstock is the opposite part of the headstock where the centering of the work part is provided on lathe machines. 
  • Cross-Slide Mechanism: Cross-slide mechanism is the sliding mechanism of the tool post which provides the movement of the tool perpendicular to the rotation axis of the work part. 
  • Carriage: Carriage is the mechanism on which the operators mount the tool post. The carriage mechanism provides the feed motion of the cutting tool along the rotational axis of the work part. 
  • Carriage Ways: Carriageways are the siling mechanisms of the carriage for the feed motion of the cutting tool on the lathe machine. 
  • Bed of the Lathe Machine: The bed of the lathe machine is the base where all the parts are carried on it. Beds are generally from cast metals to prevent the vibrations of the environment. Vibrational effects from other machines can affect the turning surface characteristics. 
  • Threaded Lead Screw Mechanism: Threaded lead screw mechanisms of the lathe machines are very important to obtain the required turning feed speed. With the increasing rotation of the lead screw mechanism, the feed motion of the carriage increases.

On the turning lathes, there are manual or digital speed and feed control where turning operators can make the required adjustments on them to obtain the required turning operation. 

Horizontal and Vertical Turning Lathes

According to the orientation of the workpiece that is to be turning, the turning machines are classified as horizontal turning machines and vertical turning machines. 

The general turning machines are horizontal in which the length of the workpiece is greater than the diameter of the workpiece. It is more convenient to place the workpiece in the horizontal direction of a turning machine if the diameter is smaller than the length of the workpiece. 

We use vertical turning machines for workpieces that have a bigger diameter compared with the length. For these workpieces also, placing them vertically is much more convenient. 

For the vertical turning lathes, the feed motion of the cutting tool is also vertical. 

How to Define the Size of Turning Machines?

Above all, there are different parameters to assess the size of the turning machines. In general, these parameters are defined by the ability of the turning machine that the biggest size of work part to machine. 

Also, the first parameter is the biggest diameter of a work part that we can attach to a turning machine. We can measure it by two times the distance between the spindle center and the carriageways. 

And also, the second parameter is the distance between the spindle and the tailstock edge. The biggest length that we can attach between the spindle. And the tailstock is the longest part that we can attach to the lathe machine. 

Types of Turning Operations

Types of turning.
Types of turning operations(Image Source: Cnclathing.com).

There are different types of turning operations that we apply for different purposes. 

  • Facing: Facing is the most common turning operation where a machine tool performs a specific depth of cut around a rotating workpiece. 
  • Taper Turning: With these turning operations, tapered geometries or cylinders which has inclined geometries are obtained. So, the feed motion of the cutting tools is the combination of the perpendicular and parallel motion according to the rotation axis of the work part. 
  • Contour Turning: We can obtain complex surface textures and shapes in these turning operations. The movement of the cutting tool is variable to obtain smooth and varying surfaces. 
  • Form Turning: We use special shaped cutting tools in form turning operations to give the direct negative shape form to the workpiece. So, cutting tools are special to obtain these forms. 
  • Chamfering: Chamfers are very important geometric features in mechanical design. We make chamfers on cylindrical geometries with chamfering machine tools. 

Other Important Applications

  • Cutoff Machining: We also call cutoff machining parting in which the cutting tool is fed perpendicular to the rotation axis of the workpiece. We obtain stepped cylindrical parts with cutoff machining operations. 
  • Threading: Threading is a special turning operation with special cutting tools to obtain threaded cylinders. We produce threads of screws with threading operations.
  • Boring: The feed and primary motions in boring operations are the same as the facing turning operations. In boring operations, a single-point tool is fed into the work part from the edge side instead of the surface. They obtain internal holes and contours with the boring operations. 
  • Drilling: We perform drilling operations in lathe machines with drill bits instead of single-point tools. The feed and primary motions in drilling operations are the same as the boring operations. 
  • Knurling: Knurling operations are special turning operations in which we obtain special knurled surfaces. In knurling operations, we use special machine tools. 

Types of Lathe Machines in Turning Operations

lathe machines.
Types of lathe machines(Image Source: Engineeringlearn.com).

Also, there are different types of lathe machines according to their configurations. We make these configurations because of different purposes. 

Turret Lathe Machine

On the turret lathe machines, the toolpost is special to hold around 6 different cutting tools. During the turning operation, these different cutting tools change rapidly for different cutting operations. So, for very high production rates that require different forms of turning operations, we use turret lathe machines. 

Speed Lathe

Speed lathes are basic constructions of lathe machines that are special for woodturning basic metal spinning and polishing operations. Unlike conventional turning machines, there are no lead screws, carriages, and cross-slide mechanisms to move the machine tool for the feed motion. So, the operator carries out the feed motion of the machine tool by the operator. In general, turning speeds are higher in the speed lathe machines. 

Toolroom Lathe

The toolroom lathe has a very similar construction to the engine lathe machine. And also, the difference between the toolroom lathe has a wide variety of speeds of tool and the workpiece. We use toolroom lathes generally for jobs that require high accuracy. 

Chucking Machine

Chucking lathe machines are also a very common type of turning machine. So, we mount the workpieces on a chuck. And there is no tailstock edge the workpiece is centered. The most important limitation of the chucking machine is that the workpieces and work parts are smaller if we compare them with engine lathe machines. 

Bar Machines

For the fixing of the work part, we use collets for the fixture instead of chucks. We can fix the long rod-like work parts inside the collets. In general, we apply cutoff operations to cut long bar-like work parts to create separate parts. Long bar-like rods can be fed from the inside of the collets in bar machines. 

Also we can use multiple spindle constructions can also in bar machines in which we can cut multiple work parts. 

CNC Lathe Machines

In mechanical lathe machines, control of the motions is performed by mechanical parts and controllers such as cams, screws, etc. In CNC lathe machines, we use the programmin codes to control the primary and secondary motions of the lathe elements. They use lots of electric motors which are controlled by electronic relays that are coded by the operator. This is the latest technology in turning operations. The acronym CNC means computer numerical control. 

Boring Machines

As we stated above, we use boring a type of machining operation to obtain internal holes on the cylindrical work parts. Also, we call boring operations internal turning operations. We can apply boring operations can as vertically and horizontally. 

Horizontal Boring Machines

In the horizontal boring machines, we mount the work part horizontally and the axis of rotation of the primary motion of the work part is horizontal. And the orientation of the machine tool is horizontal. The feed motion of the machine tool is made parallel to the axis of rotation of the workpiece. 

Vertical Boring Machines 

They also use vertical boring machines in the industry for large parts in diameter. In the vertical boring machines, work parts that they machine have diameter values bigger than the length of the work part. The rotation of the work part is vertical and the feed motion of the machine tool is vertical. 

Typical Workholding Types in Turning Operations

According to the turning type and application and the type of workpiece, there are different work-holding devices that we use in turning operations. These work holding mechanisms are 4 types. 

Mounting Work parts between Centers

In this mounting of the work part type in turning operations, we mount the work part to a spindle with a dogging mechanism. And they use the centering edge to center the work part at the tailstock of the turning machine. 

Center mounting for the work parts is suitable for the big length-to-diameter ratios. We call the tailstock side of the center the live center. And we also call the spindle side the dead center for the center mounting of the work parts in turning operations. 

Collets

Collets are special work holding mechanisms that we use to hold long-bar stocks. Long bar stocks can be fed from the collet mechanisms. So, we are not using centering in the collet mechanisms. We can attach different kinds of diameters of workpieces to collets with the grasping mechanism. 

Chucks 

Chucks are the other work holding mechanism in which they use the centering tailstock. We use self-centering features of chucks to maintain the rotation workpiece around its axis without swinging. We can adjust the jaws of the chuck mechanisms according to the size of the workpiece. 

Also, we use chuck mechanisms for the workpieces which are smaller than the workpieces in the centering operations. If we use the long toolbars in the chuck lathe mechanisms, we need to use a centering tailstock in chuckings. 

Face Plate 

Faceplate work holding mechanisms are designed to hold the irregular-shaped work parts that are needed to be turned. The holding mechanism of face plates is nearly the same as the chucks but chucks are special to hold the circular shapes generally. Also, the jaws of the face plates are special to hold the specific shape of work parts. 

Turning Operation Calculations with Calculators

In the industry, they use turning operation extensively to produce different kinds of parts and components. Like other manufacturing processes, we require strict calculations. So, you can use the calculator below to make the necessary calculations for turning operations. 

Turning operation.
Image Source: Snafu.org.

Turning Operation Calculator

You can use the turning operation calculator below to calculate all the parameters required to complete the turning operation calculations. 

Turning Operation Calculator


























Firstly, the use of the turning operation calculator is very simple above. You just need to enter the original diameter of the part, cutting speed, depth of cut in the turning operation, feed, and length of the part. After that, after the entering these values click on the ‘Calculate!’ button to calculate the required parameters related to the turning operation. If you want to make further calculations, just click on the ‘Reset’ button then re-enter the required values again. 

So, the turning operation calculator is very useful for the process designer. Furthermore, you can calculate all the turning process parameters in one shot. You can make successive calculations to obtain optimized values. 

In this calculator, the units of the entered parameters related to the turning operation, 

v: cutting speed = m/min or ft/min 

Do: original diameter = m or ft

d: depth of cut = m or ft 

f: feed = mm/rev 

L: length of workpart = mm or in

What Turning Operation Calculator Calculates?

With the turning operation calculator, you are calculating;

Rotational Speed of Turning Operation

‘N’ is the rotational speed which has the unit of rev/min. The equation is;

Rotational speed formula in turning operation.

So, in this formula, we must enter ‘v’ is the cutting speed, m/min or ft/min, and the original diameter of the part ‘Do’ which has the unit of m. Also, the rotational speed is directly proportional to the cutting speed and inversely proportional to the original diameter.

Final Diameter of the Work Part

‘Df’ is the final diameter of the work part after we complete the turning operation. The unit of the final diameter of the part is mm or in. We calculate the final diameter like this; 

Final diameter formula of rotational speed.

Furthermore, we calculate the final diameter ‘Df’ with the original diameter and the depth of cut which has the unit of m or in. With the increasing depth of cut, the speed of decrement of the diameter increases. 

Feed Rate of Turning Operation

Also, ‘Fr’ is the feed rate in the turning operation which gives the linear progression of the tool along the length of the part. The unit is mm/min or in/min. We calculate the feed rate like this for turning operations; 

Feed rate.

To calculate the feed rate, we must enter the rotational speed and the feed inside the formula. Here the unit of the feed(f) is the mm/rev or in/rev that shows how much the turning tool progresses in each revolution. With the increasing rotational speed and the feed, the total feed rate of the turning operation increases.

Total Machining Time

‘Tm’ total machining time which is the total time of the total machining operation. We calculate the total machining time or total turning time with the formula; 

Total machining time formula.

Furthermore, in this equation, you need to enter the original diameter, length of the part in mm or the feed, and the cutting speed. So, according to the turning time, turning time increases with the increasing original diameter and length and decreases with the feed and the cutting speed.

Material Removal Rate

‘Rmr’ is the material removal rate in the turning operation which has the unit of mm^3/min or in^3/min. It shows the total material removal in volume through the turning operation. Also, the material removal is calculated like this; 

Material removal rate calculation in turning operations.

To calculate the material removal rate, the cutting speed, feed, and depth of cut must be defined. Also t

Conclusion

Turning operations are very important machining and the most fundamental operations. So, there are different types of turning operations to produce different types of workpieces at different production rates. They developed lots of work part holding devices and mechanisms for turning operations. 

So, we can explain the general information about turning operations like above. 

Finally, do not forget to leave your comments and questions below about the turning operations. If you are experienced in the turning and machining sector, your comments will be very precious for us and our visitors! 

FAQs About Turning Operations

What are the main movements of turning operations?

In general, there are three movements in turning operations. The first one is the primary movement performed by the workpiece. The rotation of the work part performs the primary motion. Also, machine tools perform two secondary motions. So, we call these secondary motions feed motions both horizontal motion and vertical motion of the tool. 

Where is the turning operation used?

Turning operations are generally used in the production of heavy machinery parts such as shafts, mechanical tubes, and pipes and as additional machining processes for the improvement of surface characteristics after casting processes. Furthermore, we perform nearly all the final shaping of cylindrical parts with turning operations. 

What are the different turning operations? 

The different turning operations are; facing, taper turning, contour turning, form turning, chamfering, cutoff, threading, and boring. 

Why lathe is called the mother of all machines?

Because turning operations are the mother of all machining operations. Also, in the starting era of industrial revolutions, turning operations are started using in the production of machinery parts. 

Why do they call it an engine lathe?

It is because the use of the engine lathes in old era technologies is considered as very high technology. In these old days of machining, engine lathes are considered the machines that perform complicated tasks. So, they are called engine lathes from the old times.

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