1.7 Machine: Grinder, Drill, Lathe

Grinding

Grinding is the operation performed by means of rotating abrasive wheels for

Sharpening of tools (A)
Dressing and shaping of hardened or unhardened surfaces of work pieces (B)
Removing of uneven spots on the surfaces (C)
Finishing of round or plane parts to high accuracy of size and surface quality (From D to F)

Grinding Wheel

A grinding wheel is composed of two components as:

Abrasive grains
Bonding material

Abrasive grains are hard and sharp-edged particles of any material that has the ability to wear away a substance softer than the abrasive grain. Bonding material is the substance that has the ability to bind the abrasive particles through cohesion. A grinding wheel is made by embedding the abrasive grain in the bonding material.

Grinding Processes

The Grinding Processes are distinguished in terms of the types of grinding machine and application such as:

General hand grinding process by floor stand grinder or pedestal grinder.
Surface grinding process by surface grinding machine
Cylindrical grinding process by cylindrical grinding machine
Tools and cutters grinding process by Universal Tool and Cutter Grinder

On board the ships, the general hand grinding process is a common practice.

General Hand Grinding Process

Floor stand grinders are used for general hand grinding operations hand tools. These machines are fitted with rests for supporting the work whilst it is being ground.

Safety Rules for Grinding

Inspect wheel for cracks before mounting. The wheel is suspended through the spindle hole and lightly tapped with a mallet. The tone must be clear and ringing, without clatter or other sounds.
Test wheel for concentricity.

3.Make a test run before initial use.

4. Do not exceed the permissible circumferential speed.

5. Wear safety goggles all the time during grinding is in progress.

6. When grinding with pedestal grinder, the tool rest must be distant only 3 mm from the grinding wheel. Otherwise, the work piece may go between tool rest and wheel and break the wheel.

7. If grinding is performed without using coolant, chips must be removed by suction.

8. Do not remove the protecting wheel cover or flip up while grinding.

9.Do not touch the rotating grinding wheel.

Drill Machine

The Drilling Machine The drilling machine commonly used in general workshops is column type vertical spindle drilling machine, consists of a driving motor mounted on the vertical column. The driving motor is coupled to gear mechanism to provide variable speeds for spindle on which the twist drill is attached into the spindle bore or by means of a drill chuck. A drilling table is attached to the vertical column.

The Drilling Technique

To perform a drilling operation professionally, the correct procedure should be followed as:

Draw centre lines clearly to define the point of intersection on the work to be drilled.
Mark the point of intersection with a centre punch to provide a good work check.
Clamp the work piece in the machine vice or on the drilling table appropriately.
Select the drill of correct type and size for the job desired.
Hold the drill by appropriate means with respect to the type of shank.
Set the spindle speed.
Align the drill point with the centre punched mark.
To ensure the alignment, press the drill point against the centre punch mark and turn the spindle by hand slowly till a circle has been scribed. If the circle is concentric with the centre punch mark, the alignment is correct. Otherwise, re-align until a concentric circle is scribed.
When correct alignment is ascertained, continue drilling till the desire hole is produced.
For the holes with diameter larger than 10 mm, a pilot hole should be drilled first using a smaller drill.

Lathe Machine

Basic Machining Process

Machining is material removal process made by the use of a machine tool, which is a stationary power-driven machine that is used to shape parts made of metal or other materials. The machining processes performed on board ships are:

Turning
Drilling
Grinding

1. Turning

Turning is a metal cutting process by making the work piece to rotate about their own axis and moved against the cutting edge of the turning tool to remove the chips by the lathe. Turning process can be basically distinguished as external turning and internal turning. In detail, turning processes are distinguished not only whether external or internal but also by the shape of turned part. Therefore, there are various turning processes performed on a lathe as:

Longitudinal Turning

The turning process, in which the tool is fed along the axis of rotation of the work piece and cut the material to produce cylindrical work pieces is called longitudinal turning. Longitudinal turning operation is performed to produce cylindrical work pieces.

Transversal Turning

The turning process in which the tool is fed perpendicular to the axis of rotation of the work piece to cut the material is called transversal turning. Transversal turning is performed for two purposes as facing and side cutting.

Facing: a transverse turning process that cut the end face of the workpiece which is perpendicular to the periphery

Side Cutting: a transverse turning process to remove the slope surface and form a square shoulder

Angular Turning

Angular turning is also known as taper turning in which the tool is fed at angle to the axis of the rotation of the work piece and cut to form a taper shape.

Profile Turning

Profile turning is performed to produce various shapes or forms on the periphery of the work piece.

Thread Cutting

Thread cutting is the turning process performed to cut screw threads on the work piece by a single pointed threading tool.

Grooving

Grooving is a turning process which performed for cutting grooves on the work piece.

Major Components of a Lathe

Lathe is the machine tool that performs turning operations as employed by the lathe operator. The major components of a lathe are:

Lathe bed

Lathe Bed is the main framework of a lathe and supports the headstock, saddle, and tailstock. The surface of a lathe bed is formed as guide ways and bearing surface so that the alignment between the moving saddle and tailstock can be maintained.

Headstock

Headstock is a fully enclosed casting component and situated on the ways of the lathe bed at the left of the operator. Headstock supports the spindle and accommodates the necessary driving arrangements.

Tailstock

Tailstock is the counterpart of the Headstock. It is situated on the other end of the bed opposite the headstock. Tailstock supports the centre inside the sleeve for turning work piece between centres, and supports drills, reamers etc. for the respective operations.

Carriage Assembly Carriage Assembly is a compounded movable part which slides over the ways between the headstock and Tailstock. A carriage assembly mainly consists of the saddle and cross slide, and apron.

Saddle has a form of H and bridged across the lathe bed to carry the cross slide and to accommodate feed mechanism.

Cross Slide situated on top of the saddle provides movement of the tool at right angles to the centre line (axis) of the lathe; it also supports the compound rest, on which the tool post is attached.

Apron is fastened to the saddle, contains the gears and clutches for transmitting motions from the feed rod to the carriage so as to move the carriage or cross-slide automatically.

Compound Rest and Tool Post

Compound Rest, also called compound slide or top slide, is situated on top of the cross slide. It consists of a swivel base with a graduated scale that allows the tool clamping at an angular direction to the axis of the lathe to produce tapers.

Tool Post supports and hold lathe tools in position as required by the process. It is situated on top of the compound slide. Tool post may be distinguished as standard tool post, four-way tool post (turret tool post) and quick-change tool post.

Lead Screw, Feed Shaft, Control Shaft

Lead Screw is a long and square-threaded shaft which is running along the front of the bed. It is used for cutting screw threads in a lathe. The lead screw of a lathe is proportionately geared up to the main spindle so as to turn at speeds equal to, faster than or slower than the work piece that enables the lathe to cut the threads of varying pitches.

Feed Shaft

Feed Shaft also is a long shaft, but it is plain and formed with a key way. It runs along the front of the bed too. Feed shaft transmits feed motion to the carriage and cross slide by the mechanism installed in the apron. Feed shaft is driven by the gearing from the main spindle, and means are provided for changing the different rates of feed.

Control Shaft

Control Shaft is also known as control rod. It is a plain circular or hexagonal shaft, which runs along with lead screw, and feed shaft. Control shaft controls the operation of lathe such as switching on and off the lathe and to changing the direction of the work spindle. Control shaft is operated manually by the lathe operator.

Thread Chasing Dial

The threading dial, attached to the saddle, enables the tool to follow the same thread each time when the tool has been taken along the thread and brought back to its starting position. The dial is connected to the lead-screw by means of a worm wheel.

Chucks

Chucks used on a lathe extensively employed for holding work pieces to be turned on the lathes. Chucks are generally of two types as three-jaw self-centering chuck and four-jaw independent chuck. Size of a chuck is determined by the diameter of the chuck body.

Three-jaw chucks

Three-jaw chucks are so named because they consist of three jaws which are actuated by the scroll and move simultaneously when adjusted by the chuck wrench so that concentricity is ascertained spontaneously.

Three-jaw chucks are mainly used for holding round, triangular and hexagonal work pieces, and are available in various sizes from 4 to 16 inches (100 to 400 mm).

Four-jaw chucks

Four-jaw chucks are also so named because they have four jaws to hold the work piece. In contrast to the three-jaw chuck, the jaws are separately actuated by the square threaded screws. Therefore, the concentricity of the work is only ascertained by adjusting the jaws individually.

The jaws of a four-jaw chuck are reversible to hold the work piece from outside or from inside depending on the need of the process. Four-jaw chuck is used for holding round, square, hexagonal or irregularly shaped work piece.

Centres

Centres are work supporting devices. A lathe centre has a conical point with a Morse taper shank. Lathe centres are used to support the work piece if it cannot be held in the chuck due to its shape or surface. Varieties of lathe centres are used to suit the various operations or work piece.

The most commonly used lathe centres are made of high speed steel or high grade machine steel with carbide inserts or tips. Conical point of centres is usually 60°. Centres are generally of two kinds as dead centre and live centre.

Dead Centre

Dead Centre is the centre that does not revolve when the work piece revolves. It is supported and held in the tailstock barrel which has an internal Morse taper. Because it does not revolve as the work piece it should be lubricated from time to time during the operation. To avoid excessive friction and wear, the dead centre of a lathe should be readjusted to the work after the work piece has been revolving a short while.

Live Centre

Live Centre is a revolving centre. It is commonly used to support the work held in the chuck or when working between centres. It contains anti-friction bearings which enable the centre to revolve with the work piece. No lubrication is required between the centre and the work piece.

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