Does Your Lathe function well? 10 Concepts to understand for improving it.

Hello Readers, welcome to your own website to understand each and every topic related to manufacturing process where we transform complex content into simpler ones. In this article, we are focused to cover the meaning, material used for cutting tools, cutting speed, centre lathe, and different operations performed by the lathe process.

What is a lathe?

In machining, we use a machine tool like lathe/ shaper and a cutting tool made of a much harder material than the material of the part to be machined.

The cutting tool is given a sharp cutting edge and it is forced to penetrate inside the workpiece surface to a small depth which removes the material from the part.

The relative motion between the tool and workpiece creates a shearing action which removes the material. The thin strip of the material sheared from the workpiece is called ‘chip’.

In some cases of machining, motion is given to the workpiece and the tool remains stationary. In some other cases, the workpiece is stationary and the machine tool provides motion to the cutting tool.

What is “Red hardness”?        

Cutting tools are made of a material that can be hardened by suitable heat for red hardness.

During machining, a lot of heat is generated and the temperature of the cutting edge of the tool may reach 650-700°C.

 The tool must maintain its hardness even at elevated temperatures.

 This property of retaining its hardness at elevated temperatures is called ‘red hardness’.

Cutting tools develop the property of red hardness due to the addition of tungsten and molybdenum to high carbon steel.

What are the materials used for cutting tools?

High speed steel or tungsten carbide is used for making cutting tools.

Cutting tools made of ceramic materials (like Al2O3, SiC) and polycrystalline diamonds are also used for special applications.

What is meant by cutting speed?

If the cutting tools is stationary, the speed at which the work material approaches the cutting edge of the tool is the cutting speed. The optimum cutting speed depends on:

  • Cutting tool materials.
  • Material to be cut.
  • Whether cutting fluid is used or not.

Cutting speed is measured in meters per min.

The recommended cutting speed for machining cast iron and mild steel with high speed tools is 35 meters per minute.

If tungsten carbide tools are used, 65-70 m/min speed may be used.

What is the purpose of cutting fluid?

The purpose of using cutting fluid is to remove heat from the cutting area and to lubricate the tool faces so that the friction between chip and tool surfaces reduces. The use of cutting fluid makes the cutting process more efficient.

What is a centre lathe?

A central lathe is also called an Engine lathe or simply a lathe.

Its main function is the production of cylindrical profiles.

Centre lathe

Fig.1 Centre lathe

The main parts of the central lathe are as follows:

1. Machine bed:

It is usually made of cast iron. The main function of the machine bed is to support all the other parts. The top of the machine bed is machined in such a way that the carriage can slide along the length of the lathe.

2. Headstock:

Headstock is fixed at the extreme left hand of the bed and contains shafts and gears immersed in lubricating oil.

The driving shaft receives power from an electric motor.

The driven shaft, which is in the form of a hollow spindle, can be driven at various r.p.m by changing gears, projects out of the headstock.

A chuck (either three jaw or four jaw), is screwed on this spindle.

The workpiece can be held in the jaws of the chuck.

When the spindle rotates, the chuck as well as the workpiece held also rotates about the longitudinal axis of the spindle.

3.  Tailstock:

A tailstock is present on the right corner of the bed.

Tailstock can slide along the guideways provided on the bed and maybe brought nearer to the headstock if so desired.

Tailstock

Fig. 2 Tailstock  

The tailstock can then be clamped or fixed on the bed in that position.

The tailstock has a spindle that can be moved forward or backward by rotating a handwheel.

The front portion of the spindle carries a ‘dead’ or ‘live’ center.

When a long workpiece is held in the chuck at the headstock end, it is supported at the tailstock end by moving forward the tailstock spindle.

There has to be a small conical hole in the center of the workpiece, in which the tailstock center may be inserted to provide support.

 If the center rotates along with the workpiece, it is called a live center.

However, if the tailstock center remains stationary and the workpiece alone rotates, the center is called ‘dead center’ and the conical tip of the center has to be lubricated with grease to reduce the friction between the tailstock center and the workpiece.

4. Carriage:

The carriage can slide along the length of the machine bed from the tailstock end to the headstock end. This movement is controlled by manually operating the hand traversing wheel.

Carriage

Fig.3 Carriage

The traversing motion at different speeds can be given automatically with the help of a feed rod or feed shaft.

The carriage carries a cross slide which can be moved either manually through an automatic device.

The gears, clutches and other mechanism required for giving movement to the carriage and cross slide is hidden from view by means of an apron (thin steel plate).

What are the different kinds of operations carried out on lathe?

  • Turning
  • Facing
  • Taper turning
  • Profile turning or Form turning
  • Parting
  • Boring
  • Threading
Right hand lathe

Fig.4 Right hand lathe

What is turning operation?

In this operation, the workpiece is rotated at suitable r.p.m, so that the metal cutting may take place at the recommended cutting speed.

If ‘d’ is the diameter of the workpiece and ‘N’ the r.p.m, the cutting speed can be calculated as Π.d.N.

In the turning operation, the job rotates and the cutting tool is inserted in the surface of the workpiece.

Turning operation

Fig.5 Turning operation

The depth of a cut of 1-1.5 mm may be taken and then the tool is steadily moved from right to left by sliding the carriage on the machine bed.

The desired reduction of diameter cannot be achieved in one pass, the tool needs to be moved from right to left.

This process needs to be carried out several times to achieve the desired result.

What is facing operation?

In this operation, the workpiece is rotated as before, but the tool is moved in perpendicular direction to the workpiece. The carriage remains stationary at a fixed position. This results in creation of a flat circular section at one end of the cylinder.

What is Taper turning?

Taper turning means the production of a conical surface by a gradual reduction in diameter as we proceed along the length of the cylinder. A conical surface will be produced, if the cutting tool moves along a line which is inclined to the longitudinal axis of the workpiece instead of moving parallel to it. A taper is defined by the half angle (α) of the cone as shown in the figure.

Taper turning calculations

Fig.6 Taper turning calculations

The following methods are used for taper turning on the lathe:

  • By swiveling the compound rest.
  • By offsetting the tailstock.
  • By using a taper turning attachment.
  • By using a form tool.

FAQ’s related to lathe process:

  1. What is a lathe used for?

In machining, we use a machine tool like lathe/ shaper and a cutting tool made of a much harder material than the material of the part to be machined.

The cutting tool is given a sharp cutting edge and it is forced to penetrate inside the workpiece surface to a small depth which removes the material from the part.

The relative motion between the tool and workpiece creates a shearing action that removes the material. The thin strip of the material sheared from the workpiece is called ‘chip’.

2. What is lathe and its types?

  • Center lathe or engine lathe machine.
  • Speed lathe machine.
  • Capstan and turret lathe machine.
  • Toolroom lathe machine.
  • Bench lathe machine.
  • Automatic lathe machine.
  • Special lathe machine.
  • CNC lathe machine.

3. Why is it called an engine lathe?

A central lathe is also called an Engine lathe or simply a lathe. The reason behind this name is the similarity between the function of steam engine and lathe. Its main function is the production of cylindrical profiles.

4. What are the main parts of lathe machine?

The main parts of the central lathe are as follows:

a. Machine bed:

It is usually made of cast iron. The main function of the machine bed is to support all the other parts.

b. Headstock:

Headstock is fixed at the extreme left hand of the bed and contains shafts and gears immersed in lubricating oil.

c.  Tailstock:

A tailstock is present on the right corner of the bed. Tailstock can slide along the guideways provided on the bed and maybe brought nearer to the headstock if so desired.

d. Carriage:

The carriage can slide along the length of the machine bed from the tailstock end to the headstock end.

5. Should you wear gloves when operating a lathe?

The operator should not wear gloves as it might get stuck while the machine is operating.

6. Who is father of lathe machine?

David Wilkinson is the father of lathe machine.

CONCLUSION:

We have covered all the important concepts related to lathe process. Hope you all are crystal clear with all the concepts mentioned here. If you have any questions please use the comments section to get in touch with us. Till then have fun and always keep reading!

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