BORING MACHINES: Classification of Boring Machines, Horizontal Boring Machine, Floor type Horizontal Boring Machine, Planer type Horizontal Boring Machine, Multiple Head type Horizontal Boring Machine

BORING MACHINES:

The operation of a boring is enlargement of an already existing hole. This hole can be due to previous drilling, or produced in casting or forging. Small holes, particularly in small jobs the boring operation can easily done on centre lathe or capstan and turrets of medium size. For large and heavy jobs special boring machines are used, which make the operation easy and efficient. These machines are production machines for boring on a large scale.

Classification of Boring Machines:

Boring machines are manufactured in various different designs & sizes. They can be broadly classified in to the following three types.

1. Horizontal Boring Machines.

2. Vertical Boring Machine.

3. Jig Boring Machine.

The first two types are production machines used in general production work, the last one is a precision machine, used for precision boring operations, such as Jig Boring.

Horizontal Boring Machine:

Horizontal boring machines are of various types such as Table type, Planer type, Floor type, and Multiple head type etc each of these suitable for a certain range of operations, but of all these the table type or universal type is most versatile and commonly used. The spindle of this machine is capable of holding drills, and milling cutters as well to perform the operations of drilling and milling hence this machine is called horizontal boring, drilling and milling machine.

The principal parts of this type of machine are:

1. Two vertical columns, one on each end of the table.

2. A head stock which can be moved vertically, along the main column.

3. A horizontal spindle, suitably housed in the head stock, which can be rotated and fed forward and backward according to requirement.

4. A load bearing end support, for supporting the end of a long boring bar, which can be adjusted vertically along the end support column.

5. A horizontal table, mounted on a saddle that can be moved horizontally forward and backward and sideways by moving the saddle.

6. A heavy and strong bed, which carries the entire load of different parts, work piece and tooling over it.

Floor type Horizontal Boring Machine:

This machine is comparatively heavier type of horizontal boring machine. The operating and spindle supporting units are not mounted on a bed, as in the table type machine, but are carried on separate run ways, which facilitates the movement of these units, together with the spindle past the work. 

The work does not move at all, but is kept stationary at a platform floor plate. It is this relative movement of work with respect to the other units of the machine in which it differs from the table type machine. This type of the machine is very suitable for long and heavy jobs.

Planer type Horizontal Boring Machine:

This machine resembles in construction with the table type. The only difference in the construction and operation of the work supporting mechanism. In this a heavy cross-bed is incorporated between the spindle column and the end support column. This bed is mounted across the axis of the spindle and carries a table over it. On its two sides it carries two columns.

The main column carrying the head stock, is rigidly fixed, whereas the end-support column can move towards or away from this bed along the horizontal ways provided on the top of the cross bed, at right angles to the former bed.

The job is mounted on the table. In operation, it resembles a planner in that the tool is held between the two columns or mounted on the head stock only and the work, mounted on the table, moves past the tool. This type of machine is very suitable for long jobs.




Multiple Head type Horizontal Boring Machine:

It consists of two vertical columns mounted on the sides of a stationary bed. The columns are bridged by means of a cross-rail. As a maximum four head stock can be mounted on the machine, one each on the two vertical columns and two on the cross-rail. The head stock on the columns will have horizontal spindles and those on the cross-rail vertical spindles. In this way maximum four tools can be mounted simultaneously on this machine.

The work is mounted on the table, which is supported and moved on the bed. This machine resembles a planer type milling machine. The head stocks can be swiveled to desired angles if angular cuts are required to be taken. Machining on more than one surface on a job is possible simultaneously as up to four tools can operate simultaneously on the job from different angles and at different locations.




Vertical Precision Boring Machine:

It is a production machine basically designed for boring holes in cylinder blocks and liners of automobile engines, fine boring of parts in Ferrous and non ferrous metals etc.

Constructional Features:

Column and Base: 

The vertical column is a cast Iron box type casting with stiffening ribs inside. The base is another massive cast Iron structure and carries guide ways at its top face, along which table traverse column and base are fastened together rigidly. Prismatic guide ways are provided on the front face of the column along which the spindle head moves up and down. Lead screw of the spindle head is located between the two vertical ways at the front face of the column.

Spindle Head: 

It traverses in vertical direction along the column ways. The spindle head housing carries inside it the v- belt drive for spindle and hand traverse mechanisms.

According to the size of the hole to be bored, one of the three inter changeable spindles, provided with the machine is mounted on the spindle head. A screw is provided with the machine is mounted on the spindle head. A screw is provided on the tool holder face for adjustment of overhang of the boring tool. A special dial is provided to show precision adjustment of the tool up to 0.02mm.

Speed and feed gear box: 

It is mounted inside the column on the machine base. It transmits the motion from the electric motor to the shaft of the spindle drive and to the lead screw of the indle head. The gear box provides 6 spindle speeds and 4 feeds and also rapid traverse to the spindle.

Table: 

It is made in two parts. The lower part moves in cross direction along ways provided on the base and the upper one in longitudinal direction along the ways provided on the top of the lower part. During the operation the table can be locked by means of stops to prevent its movement in either direction.

Salient Features:

1. The machine is highly rigid and vibration proof, maintains its initial accuracy of performance over a long period of time.

2. The control of speed and feed gear box is conveniently grouped in an easy to reach place and is performed by means of three levers.

3. Most of the machine units are assembled in independent housings which facilitates easy repair.

4. The table being movable in two directions permits to bore several holes in a work piece at one setting.

5. The upper limit of the spindle speed, ample power of motor and rigidity of the machine permit the use of carbide cutting tools.

6. Precision antifriction spindle bearing ensure machine durability, accuracy and surface finish.

Vertical Boring Machines:

In this the work is held on a rotary table, rotates about a vertical axis, while the tool remains stationery, except for feeding. The table together with the work rotates in a horizontal plane.

Thus if the table is considered to have replaced the chuck or face plate of a centre lathe, this machine can be considered as a vertical lathe with its bed working as a head stock mainly the

following three types of boring machines in this category.

1. Standard Vertical boring mills.

2. Vertical Turret Lathes.

3. Vertical Precision Boring Machines.

Standard Vertical Boring Mills: 

It consists of a heavy Cast iron bed, which carries a circular table over it. On the sides of the bed are two vertical columns which are bridged together by means of a cross-rail. As a maximum four tool heads can be mounted on the machine one each on the two columns and two on the cross-rail. This number can also be reduced according to the requirements. Usually the tool heads carry the provision for being swiveled to a certain angle for taking angular cuts. The work is mounted on the table which rotates about its vertical axis. the rotating work is thus, fed against fixed tools, which results in circular cuts being taken on the job. The table is provided with T-slots for clamping the work.

Usually large symmetrical work pieces, such as cylindrical objects are bored on these machines. A few examples are the casings for steam turbines, tables for machine tools and pressure vessels. Vertical housing on the two sides of the table limits the size of the work.

The maximum size of the work would be equal to dia. of the table and same will represent the size of the machine.

Vertical Turret Lathe: 

It has a special advantage that many tools can be simultaneously mounted on the turret head, and therefore, a large number of different operations can be performed in addition to boring a single setting of work. The table of the machine is of rotary type and carries adjustable jaws for clamping the work.

The rotary table rotates over the bed, about a vertical axis. The work piece is held over this table. Maximum two side tool posts can be mounted, one each on each column.

These tool posts can be adjusted vertically and they can also move forward and backward.

One or two vertical tool heads can be mounted on the cross-rail, which can be adjusted horizontally along the cross-rail. Each vertical tool head will carry a turret head enabling to mount a number of tools in sequence on it to enable different operations to be performed in a single setting of tools. The turret head can be indexed after each operation, to bring the proper tool in position for the next operation. The vertical tool head can also be moved, upwards anddown wards, according to requirement.

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