In this article, we will learn about what are the different types of lathe machine operations performs on the lathe.
Lathe machine performs the different operation such as turning, facing, taper turning, knurling, grooving, parting off, electric turning, thread cutting, reaming etc.
Let’s discuss all lathe machine operations one by one as follows.
To perform different lathe machine operations on a lathe, the workpiece may be supported and driven by any one of the following methods:
- Workpiece held between centres and tool driven by carriers and catch plates.
- Workpiece held on a mandrel which is supported between centres and driven by carriers and catch plates.
- Held and driven by chuck with the other end supported on the tailstock centre.
- Held and driven by a chuck or a faceplate or an angle plate.
The above methods of holding the work may be classified under two heading:
- Workpiece held between centres.
- Workpiece held by a chuck or any other fixtures.
Lathe Machine Operations
The lathe machine operations are classified into three main categories.
Lathe machine operations done either by holding the workpiece between centres or by a chuck are:
- Plain or Straight Turning
- Rough Turning
- Shoulder Turning
- Taper Turning
- Eccentric Turning
- Thread cutting
- Spring Winding
Lathe machine operations which are performed by holding the work by a chuck or a faceplate or an angle plate are:
- Taper boring
- Internal thread cutting
The operation which is performed by using special attachments are:
1. Lathe machine operations (workpiece between centres)
done by holding the workpiece between centres or by a chuck are:
It is the most common type of operation in all lathe machine operations. Turning is the operation of removing the excess material from the workpiece to produce a cylindrical surface to the desired length.
The job held between the centre or a chuck and rotating at a required speed. The tool moves in a longitudinal direction to give the feed towards the headstock with proper depth of cut.
The surface finish is very good.
1.1 Straight Turning:
The workpiece is held on the chuck and it is made to rotate about the axis, and the tool is fed parallel to the lathe axis. The straight turning produces a cylindrical surface by removing excess metal from the workpiece.
1.2 Rough Turning:
It is the process of removal of excess material from the workpiece in a minimum time by applying high rate feed and heavy depth of cut. in rough turning the average depth of cut 2mm to 4mm can be given and feed is from 0.3 to 1.5mm per revolution of the work.
1.3 Shoulder Turning:
When a workpiece has different diameters and is to be turned, the surface forming steps from one diameter to the other is called the shoulder, and machining this part of the workpiece is called shoulder turning.
1.4 Taper Turning:
- A ”taper” is the uniform increase or decrease in the diameter of the workpiece and measured along with its length.
- Taper turning means to produce a conical shape by a gradual reduction in diameter from a cylindrical workpiece.
The amount of taper in the workpiece is usually specified on the basis of the difference in diameter of the taper to its length. It is known as a cone and it is indicated by the letter K.
It has the formula K = D-d / 1 to produce the taper on the workpiece.
- D = Larger diameter of taper.
- d = Small diameter of taper.
In case of lathe, the taper on a given workpiece is obtained by tuning the job and feeding the tool at an angle to produce a gradual increase or decrease in the diameter of the workpiece.
- The two important types of tapers are,
- ”More taper” here, the angle is very small and varies from 1.4 to 1.5°.
- ”Metric taper” is available in seven standard sizes with standard taper angles.
- Methods of taper turning,
- Form tool method
- Combined feeds method
- Compound rest method or swivelling compound rest method
- Tailstock set over method
- Taper turning attachment method
1.4.1 Form tool method
Here the taper length obtain is equal to the width of the form tool. To obtain the required size of the taper the form tool is fed slowly straight into the workpiece by operating the cross slide perpendicular to the lathe axis.
This is the simplest method of taper turning.
It is limited to obtain small taper length such as chamfering the side of the workpiece. The method is done at a faster rate.
1.4.2 Combined feeds method
The combined feed is made with the movement of a tool in longitudinal and lateral direction simultaneously while moving the workpiece.
The taper, which we are going to obtain, is equal to the resultant to the magnitude of the longitudinal and lateral feeds.
Changing the feeds rates in both directions can change the direction and the taper angle.
1.4.3 Compound rest swivel method
Here the workpiece rotates and the tool is fed at an angle by swivelled compound rest.
The base of the compound rest is graduated in degrees.
The taper angle is the angle at which the compound rest to be rotated is calculated by using the formula tanα = D-d / 21, where, D= bigger diameter, d = smaller diameter, l = length of the workpiece.
Compound rest can be swivelled to the required angle α.
Once the compound rest is set to particular angle then the tool is moved by compound rest and wheel.
1.4.4 Taper turning attachment method
- This method is similar to the compound rest method.
- Here the job or workpiece rotates and the tool is fed at the taper angle α.
- In this, arrangement, which has guide block graduated in degrees, with the help of this the block can be required taper angle to the lathe axis.
- The taper angle is calculated similarly to compound rest method using the formula: tanα = D-d / 21.
1.4.5 Advantages of taper turning attachment method:
- Internal tapers can be obtained accurately.
- large size tapers can be easily obtained.
- Once the attachment is set the taper turning operation can do at a faster rate.
- By setting the taper angle to ‘zero’ we can carry out plain turning.
1.4.6 Disadvantages of taper turning attachment:
- It requires additional mounting facilities.
- Fitting and removing attachment consume more time.
- The attachment has to take large forces.
Tailstock set over method
The tailstock set over arrangement is made as shown in the figure.
Here the workpiece on the job is tilted at the required taper angle. The tool is fed parallel to the axis.
The tilting of the workpiece or the job to the required taper angle is achieved by the movement of tailstock with the help of tailstock set over the screw. This method is useful for small tapers.
1.5 Eccentric turning
When a cylindrical surface two separate axis of rotation, with the first axis, is offset to the other axis then such a workpiece is machined by the operation called eccentric turning.
Here three sets of centre holes are drilled.
By holding the workpiece at these three centres the machining operation for each of the surface can be completed.
It is an operation of reducing the length of the workpiece by feeding the perpendicular to the lathe axis. This operation of reducing a flat surface on the end of the workpiece. For this operation, regular turning tool or facing tool may use. The cutting edge of the tool should set to the same height as the centre of the workpiece.
- Facing consist of 2 operations
- Roughing: Here the depth of cut is 1.3mm
- Finishing: Here the depth of cut is 0.2-0.1mm.
3. Chamfering operation
It is the operation of getting a bevelled surface at the edge of a cylindrical workpiece. This operation is done in case of bolt ends and shaft ends. Chamfering helps to avoid damage to the sharp edges and protect the operation getting hurt during other operations.
Chamfering on bolt helps to screw the nut easily.
4. Knurling operation
It is an operation of obtaining a diamond shape on the workpiece for the gripping purpose. This is done to provide a better gripping surface when operated by hands. It is done using a knurling tool. The tool consists of a set of hardened steel roller, and it is held rigidly on the toolpost.
Knurling is done at the lowest speed available on a lathe. It is done on the handles and also in case of ends of gauges. The feed varies from 1 to 2 mm per revolution. Two or three cut may be necessary to give the full impression.
5. Thread cutting
It is the important operation in the lathe to obtain the continuous ”helical grooves” or ” threads’‘.
When the threads or helical grooves are formed on the out surface of the workpiece is called external thread cutting. When the threads or helical grooves are formed on the inner surface of the workpiece is called internal thread cutting. The workpiece is rotating between the two centres i.e., live centre and dead centre os the lathe.
Here the tool is moved longitudinally to obtain the required type of the thread. When the tool is moved from right to the left we get the left-hand thread. Similarly, when the tool is moved from left to the right we get the right-hand thread.
Here the motion of the carriage is provided by the lead screw. A pair of change gears drives the lead screw and by rotating the handle the depth of cut can be controlled.
It is the finishing operation performed after turning. This is done on a lathe to remove burrs, sharp corners, and feed marks on a workpiece and also to bring it to the size by removing the very small amount of metal.
The operation consists of passing a flat single cut file over the workpiece which revolves at a high speed. The speed is usually twice that of turning.
This operation is performed after filing to improve the surface quality of the workpiece. Polishing with successively finer grades of emery cloth after filing results in very smooth, bright surface. The lathe is run at high speeds from 1500 to 1800m per min, and oil is used on the emery cloth.
It is the process of reducing the diameter of a workpiece over a very narrow surface. It is done by groove tool. A grooving tool is similar to the parting-off tool. It is often done at the end of a thread or adjacent to a shoulder to leave a small margin.
it is the process of forming a thin sheet of metal by revolving the job at high speed and pressing it against a headstock spindle. A support is also given from the tailstock end.
10. Spring Winding
Spring winding is the process of making a coiled spring by passing a wire around a mandrel which is revolved on a chuck or between centres. A small hole is provided on the steel bar, which is supported by Tool Post and the wire is allowed to pass through it.
It is the process of turning a convex, concave or of any irregular shape. Form-turning may be accomplished by the following method:
- Using a forming tool.
- Combining cross and longitudinal feed.
- Tracing or copying a template.
Forming tools are not supposed to remove much of the material and is used mainly for finishing formed surfaces. Generally, two types of forming tools are used straight and circular. Straight type is used for wider surface and the circular type for narrow surfaces.
2. Lathe machine operations (holding the work by a chuck)
performed by holding the work by a chuck or a faceplate or an angle plate are:
Drilling is the operation of producing a cylindrical hole in a workpiece. It is done by a rotating tool, the rotating side of the cutter, known as drilling drill.In this operation, The workpiece is revolving in a chuck or a faceplate and the drill is held in the tailstock drill holder or drill chuck.
The feeding is adopted is affected by the movement of the tailstock spindle. This method is adopted for the drilling regular shaped workpiece.
Reaming is the operation of finishing and sizing a hole which has been already drilled or bored. The tool is used is called the reamer, which has multi-plate cutting edges.
The reamer is held on the tailstock spindle, either directly or through a drill chuck and is held stationary while the work is revolved at a very slow speed.
Boring is the operation of enlarging the hole which is already drilled, punched or forged. It cannot produce a hole. Boring is similar to the external turning operation and can be performed in a lathe. In this operation, the workpiece is revolved in a chuck or a faceplate and the tools which are fitted to the tool post is fed into the work.
It consists of a boring bar having a single point cutting tool which enlarges the hole. It also corrects out of roundness of a hole. This method adopted for boring small-sized works only. The speed for this process is slow.
Counterboring is the operation of enlarging the end of the hole through a certain distance.
it is similar to a shoulder work in external turning. The operation is similar to boring and plain boring tools or a counterbore may be used.
The tool is used called as a counterbore. The speed is slightly less than drilling.
5. Taper Boring
The principle of turning a tapered hole is similar to the external taper turning operation and is completed by rotating the work on a chuck or a faceplate.
The feeding tool is at an angle to the axis of rotation of the workpiece.
A boring tool is mounted on the tool post and by swivelling the compound slide to the desired angle, a short taper hole is machined by hand feeding.
Tapping is the operation of cutting internal threads of small diameter using a multipoint cutting tool called the tap.In a lathe, the work is mounted on a chuck or on a faceplate and revolved at a very slow speed.
A tap of required size held on a special fixture is mounted on the tailstock spindle.
Undercutting is similar to grooving operation when performed inside a hole. It is the process of boring a groove or a large hole at a fixed distance from the end of a hole.
This is similar to the boring operation, except that a square nose parting is used.
Undercutting is done at the end of an internal thread or a counterbore to provide clearance for the tool or any part.
3. Lathe machine operations (using special attachments)
which are performed by using special attachments are:
Milling is the operation of removing metal by feeding the work against a rotating cutter having multiple cutting edges.
For cutting keyways or grooves, the work is supported on the cross-slide by a special attachment and fed against a rotating milling cutter held by a chuck. The depth of cut is given by vertical adjustment of the work provided by the attachment.
The depth of cut is given by verticle adjustment of the work provided by the attachment. The feeding movement is provided by the carriage and the vertical movement of the cutter is arranged in the attachment.
Grinding is the operation of removing metal in the form of minute chips by feeding the work against a rotating abrasive wheel known as the grinding wheel.
Both internal and external surface of a workpiece may be ground by using a special attachment mounted on the cross slide. For the grinding external surface, the work may be revolved between centres or on a chuck. For internal grinding, the work must be revolved on a chuck or faceplate.
The feeding is done by the carriage and the depth of cut is provided by the cross slide. Grinding is performed in a lathe for finishing a job, sharpening a cutter, or sizing workpiece after it has been hardened.
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