WSDT - Advanced Design Technology

machining

CENTRE LATHE

The principle of the CENTRE LATHE is fairly straight forward to understand. The piece of material is rotated and a cutting tool is brought up to the rotating material. The depth of cut is varied by moving the tool further into the metal and the length of cut by moving the tool along or across the metal. To assist with the cutting most lathes pump a combined coolant and lubricant onto the work. This prevents the work and the cutting tool becoming too hot which reduces the sharpness of the tool and therefore the surface finish.The speed at which the lathe turns is variable and this speed depends on the material being cut and the diameter of the material. The rule is - the larger the diameter and the harder the material, the slower the speed. A piece of ALUMINIUM would be turned at a faster speed than STEEL.The drawing below shows a CENTRE LATHE.

 

The material is normally held in a CHUCK; either of the 3 or 4 JAW variety. Both types can be obtained either the SELF CENTERING or INDEPENDENT type. With the SELF CENTERING one all the jaws move together. With the INDEPENDENT one each jaw is adjusted individually.

 

Round or hexagonal section material is held in a 3 JAW SELF CENTERING CHUCK and square section material is held in a 4 JAW SELF CENTERING CHUCK.

Irregular shaped pieces of material can be held in a 4 JAW INDEPENDENT CHUCK.

On lots of chucks the jaws are reversible but it is important to remember that the jaws are numbered and so are the slots they fit into. They may look the same but they are different on the back so make sure each chuck fits into its correct slot and they must be fitted in numerical order otherwise they will not meet in the centre.

Long pieces of material are supported at both ends by using the TAILSTOCK CENTRE. This can be a REVOLVING CENTRE (which funnily enough revolves) or of the DEAD CENTRE type which is stationary. The drawing of the lathe above shows a DEAD CENTRE.

A REVOLVING CENTRE is shown opposite.

 

 

DRILLING ON THE LATHE

When drilling on the lathe the drill is stationary and the work revolves. This is the opposite to drilling on the PILLAR DRILL (see DRILLING METAL).

The drill is held in a CHUCK in the TAILSTOCK of the lathe. The work rotates and the drill is moved up to the work by turning the wheel on the end of the TAILSTOCK.

Before using a TWIST DRILL a CENTRE DRILL should always be used on a slow speed to locate the centre of the bar being drilled. A normal TWIST DRILL does not go to a point and will not find the centre.

The drawing opposite shows the Twist Drill in the Tailstock after first drilling with the Centre Drill.
 

 

FACING OFF

Facing off is one of the most used processes on a metal lathe.

The lathe tool is moved across the end of the piece of material and with the use of the Cross Slide and the Compound Slide a series of small cuts are taken off to produce a very high quality finish.

   

TURNING TO SIZE

Turning to size is another one of the most used processes on a metal lathe.

The lathe tool is moved along the piece of material and with the use of the Cross Slide and the Compound Slide a series of small cuts are taken off to produce a very high quality finish.

 

 

KNURLING

Knurling is a process which forms diagonal raised sections of metal onto the surface of the metal to provide grip. Hard grooved wheels are pressed slowly into the work and the wheels are moved along the metal.

The KNURLING TOOL fits into the tool holder and the work is held in the chuck. If the work is long then a DEAD CENTRE is used to support the other end of the metal as a lot of sideways force is applied to the work.

The drawing opposite shows the set up.

 

 

BORING

Boring is inside turning and is done with a special lathe tool called a BORING BAR. The bar fits into the Tool Holder and the Compound Slide moves the bar into the work. The majority of the metal is first removed with drilling.

The drawing opposite shows the set up.

 

 

TAPER TURNING

A small taper, called a CHAMFER can be put onto a piece of metal by sharpening a tool up to the required angle. This is quite useful for finishing the end of a bar off. Instead of a chamfer a small radius could be put onto the bar by sharpening up a suitable tool.

This is shown opposite and the animation is shown below.

To produce longer tapers then the Compound Slide is adjusted to the required angle and the lathe tool is moved along by the wheel at the end of the slide.