Lathe Specifications, Parts & Operations

Lathe Specifications, Lathe Parts & Lathe Operations

Engine Lathe or Centre Lathe:

The main parts of the centre lathe are:

(i) Bed, (ii) Headstock, (iii) Tailstock, (iv) Carriage, (v) Feed mechanism

Headstock:

           Headstock is secured permanently to the inner ways at the left-end on the bed and it provides mechanical means of rotating the work at different speeds. It comprises of the power source, power transmission gear box and a hollow spindle. Live centre, face plate, collet or chuck can be fitted to the spindle nose to hold and drive the work. Headstock spindle is driven through a stepped pulley and a belt or by transmission gears in the headstock. The main gear box provides the necessary spindle speeds, considering the range of materials to be turned and sizes. It also houses the feed gear box to provide the various feed rates for thread cutting ranges and normal turning.

Tailstock:

           The tailstock is located on the innerways at the right-end on the bed. Tailstock has two main uses,

(i) It is used for supporting the right end of the workpiece. (ii) It is also used for holding and feeding the tools such as drills, reamers, taps etc. Tailstock is a non rotating support but can be moved left or right along the inner guideways to adjust to the length of the workpiece. When supporting heavy jobs, live centre is used which rotates along with the job.

Carriage:

The carriage of a lathe controls and supports the cutting tool. It consists of the following parts;

(i) Saddle:

It is an H-shaped casting that fits over the bed and slides along the bed ways. It carries the cross slide and tool post.

(ii) Cross-slide:

Cross slide is mounted on the carriage. It carries the compound rest and the tool post. It gives cross feed to the cutting tool in a direction perpendicular to the axis of rotation thus varying the depth of cut or facing the end surface.

(iii) Compound rest:

Compound rest is fitted on the top of the cross-slide and is used to support the cutting tool. It can be swivelled to any angle for taper turning operations and is moved manually.

(iv) Tool post:

The tool post is mounted on the compound rest and the tool is clamped to it. It can _be rotated so that the cutter is held at the correct position required for the job.

(v) Apron:

Apron mechanism:

            This mechanism is used to convert the rotary motion of the feed rod and lead screw into feed motion of the carriage. There are various designs of this mechanism made by different makers. Power is transmitted from feed rod to the worm wheel through gears A,B,C,D and worm. The splined shaft attached to the worm wheel is always engaged with the gears F and G. A knob E is fitted with the feed check shaft. This can be placed in three positions such as neutral, push-in and pull-out. When the knob E is in neutral position, power is not transmitted either to cross feed screw or to the carriage. When the knob E is in push-in position, rotating gear G will be engaged to H. Then the power will be transmitted to pinion I and automatic longitudinal feed takes place. When the knob E is in pull-out position, rotating gear F will be engaged to K. So the power is transmitted to cross feed screws through L. This leads to automatic cross feed. For thread cutting, half nut is engaged by half nut lever after putting knob E in neutral position. Both longitudinal and cross feed can be reversed by operating the tumbler gear mechanism.

Feed rod:

            Feed rod is a long shaft that has a keyway. The power is transmitted from the lathe spindle to the apron gears through a feed-rod via a large number of gears. The feed-rod is used to move the carriage or cross slide for turning, boring and facing.

Lathe Specification:

The size of a lathe is specified as follows;

•The height of the centre measured over the lathe bed

•Swing or maximum diameter: That can be rotated over the bed ways.

•Swing or diameter over carriage is the largest diameter of work that will revolve over the lathe saddle.

•Maximum job length in mm that may be held between the centres [headstock and tail-stock centres].

•Bed length in metres which may include the headstock length also.

•Diameter of the hole through lathe spindle for turning bar material.

In addition to the above, the following specifications are necessary while ordering a lathe:

•The length, width and depth of bed.

•The depth and width of the gap, if it is a gap lathe

•The swing over gap.

•The number and range of spindle speeds.

•The number of feeds.

•The lead screw diameter.

•The number and range of metric threads that can be cut.

Chucks:

            Chucks are used to hold workpieces of short length and large diameters or irregular shapes. This is attached to the lathe spindle and the work is held between the jaws of the chuck. Some of the commonly used chucks are,

(i) Three jaw universal chuck for circular objects

(ii) Four jaw independent chuck.

(m) Magnetic chuck.

(iv) Collet chuck.

•Three jaw universal chuck:

            This chuck has three jaws. When chuck key is turned, all the jaws will move equal distance in radial direction and work is centered automatically.

•Four jaw independent chuck:

            This chuck has four jaws and each jaw can be moved independently. These jaws have rotating screw which meshes with the teeth cut on the underside of the jaw. Concentric circles are inscribed on the face of the chuck for quick centering of work pieces. It can be used for non-circular object like turning of shank on a hexagonal headed bolt.

Rests:

            Provide additional support for long work pieces. It helps to prevent deflection of work piece under the action of cutting force of tool. The use of rest is recommended where the length of work piece is 10 to 12 times the diameter.

Types of rests:

(i) Steady Rest

(ii) Follower Rest

•Steady rest:

            Steady rest is clamped on the bed ways in the required position between head stock and tail stock. Used when a long piece is machined or drilled at its end by holding the job in a chuck. It avoids the chances of deflection of job at the other end.

•Follower rest:

            It is mounted on lathe saddle and moves together with the carriage. It performs the same function as the steady rest but it has two jaws which support the work opposite to the tool.

Lathe operations:

•Facing:

Facing is an operation which produces flat surfaces. In this operation the too] is fed at right angles to the axis of the work piece.

•Turning:

Turning is the machining operation in which excess material is removed by rotating the work piece against a cutting tool.

•Grooving:

It is the process of reducing the diameter of the workpiece over a very narrow surface.

•Drilling:

It is the process of making hole on work piece. The drill is fed slowly into the work piece which is revolving in a chuck. The drill is held stationary in the tail stock spindle.

•Reaming:

Reaming is the process of making hole smoothly and accurately to the size. The work with drilled hole is held in a chuck and reamer is inserted in tail stock spindle and rotated.

•Boring:

Boring is the operation of enlarging the previously drilled hole with the aid of single point cutting tool called boring tool. If the hole is enlarged only through a certain length then it is referred as counter boring. If the tool is fed at an angle to the axis of rotation it is called internal taper turning.

•Parting – Off:

Parting-off is the operation of separating the finished work piece from a bar stock. The operation involves feeding the cutting tool into the rotating work piece .

•Threading:

Cutting helical groove over a cylindrical or conical workpiece is called thread cutting.

END