Workshop Practice

Module 6. Lathe machine, drilling machine etc

Lesson 11
INTRODUCTION TO DRILLING MACHINE

11.1 Introduction

The drilling machine is one of the most important machine tools in a workshop. As regards its importance, it is second only to the lathe. In a drilling machine holes can be drilled quickly and at low cost. The hole is generated by the rotating edges of a cutting tool known as the drill which exerts large force on the work clamped on the table. As the machine tool exerts a vertical pressure to originate a hole it is loosely called a drill press. Drilling machines are made in many types and sizes, each is designed to handle a class of work or specific jobs to the best advantage.

Types of drilling machines :

1. Portable drilling machine
2. Sensitive drilling machine
3. Upright drilling machine
4. Radial drilling machine
5. Gang drilling machine
6. Multiple spindle drilling machine
7. Automatic drilling machine
8. Deep hole drilling machine

11.2 Sensitive Drilling Machine

It is a small machine designed for drilling small holes at high speeds in light jobs. It may be bench or floor mounted. It consists of a base, a vertical column, horizontal table, a head supporting the motor and driving mechanism and a vertical spindle for driving and rotating the drill.Total drilling operation is manually controlled. The machine is capable of drilling holes from 1.5 to 15mm diameter.

Fig. 11.1 Sensitive drilling machine

11.3 Upright Drilling Machine

The upright drilling machine is designed for handling medium sized workpieces. In an upright drilling machine a large number of spindle speeds and feeds may be available for drilling different types of work. The table of machine also has different types of adjustments. There are two general classes of upright drilling machine:

(1) Round column section or pillar drilling machine

(2) Box column section

11.3.1 Round column section or pillar drilling machine

The round column section upright drilling machine or pillar drilling machine consists of a round column that rises from the base which rests on the floor,an arm and a round table assembly, and a drill head assembly.

The arm and the table have three adjustments for locating work pieces under the spindle. The arm and the table may be moved up and down on the column for accommodating work pieces of different heights. The table and the arm may be moved in an arc up to 180⁰ around the column and may be champed at any position. This permits setting of the work below the spindle.

This is particularly intended for lighter work. The maximum size of hole that the machine can drill is not more than 50 mm.

11.3.2 Box column section upright drilling machine:

The upright drilling machine with box column section has the square table fitted on the slides at the front face of the machine column. Heavy box column gives the machine strength and rigidity. The table is raised or lowered by an elevating screw that gives additional support to the table. These special features permit the machine to work with heavier work pieces, and holes more than 50 mm in diameter can be drilled through this machine.

11.4 Radial Drilling Machine

The radial drilling machine is intended for drilling medium to large and heavy workpieces. The machine consists of a heavy, round, vertical column mounted on a large base. The column supports a radial arm which can be raised and lowered to accommodate work pieces of different heights.

The arm may be swung around to any position over the work bed. The drill head containing mechanism for rotating and feeding the drill is mounted in a radial arm and can be moved horizontally on the guide-ways and clamped at any desired position.

These three movements in a radial drilling machine when combined together permit the drill to be located at any desired point on a large work piece for drilling the hole. (Fig. 11.2)

11.4.1 Plain radial drilling machine

Ina plain radial drilling machine provisions are made for vertical adjustment of the arm, horizontal movement of the drill head along the arm, and circular movement of the arm in horizontal plane about the vertical column.

11.4.2 Semi universal machine

Ina semi universal machine, in addition to the above three movements, the drill head can be swung about a horizontal axis perpendicular to the arm. This fourth movement of the drill head permits drilling hole at an angle to the horizontal plane other than the normal position.

11.4.3 Universal machine

Ina universal machine, in addition to the above four movements, the arm holding the drill head may be rotated on a horizontal axis. All these five movements in a universal machine enable it to drill on a work piece at any angle.

11.5 Gang Drilling Machine

When a number of single spindle drilling machine columns are placed side by side on a common base and have a common work-table, the machine is known as the gang drilling machine.

In this machine four to six spindles may be mounted side by side. This type of machine is specially adapted for production work. A series of operations may be performed on the work by simply shifting the work from one position to the other on the work-table. Each spindle may be set up properly with different tools for different operations.

11.6 Multiple – Spindle Drilling Machine

The function of a multiple-spindle drilling machine is to drill a number of holes in a piece of work simultaneously and to reproduce the same pattern of holes in a number of identical pieces in a mass production work. Such machines have several spindles driven by a single motor and all the spindles holding drill are fed into the work simultaneously. Feeding motion is usually obtained by raising the work-table.

11.7 Drilling Operations (Fig. 11.3)

The operations that are commonly performed on drilling machines are

1. Drilling,

2. Reaming ,

3. Boring,

4. Counter-boring,

5. Counter-sinking,

6. Spot-facing

1. Drilling: This is the operation of making a circular hole by removing a volume of metal from the work piece by a cutting tool called drill.
   
2. Reaming: This is the operation of sizing and finishing a hole already made by a drill. Reaming is performed by means of a cutting tool called reamer having several cutting edges. Reaming serves to make the hole smoother, straighter and more accurate in diameter. Reamer may be classified as solid reamer and adjustable reamer.
   
3. Boring: This is the operation of enlarging a hole by means of adjustable cutting tools with only one cutting edge. A boring tool is employed for this purpose.
   
4. Counter-boring : This is the operation of enlarging the end of a hole, as for the recess for a counter-sunk rivet. The tool used is known as counter-bore.
   
5. Counter-sinking : This is the operation of making a cone-shaped enlargement of the end of a hole, as for the recess for a flat head screw.
6. Spot – facing: This is the operation of removing enough material to provide a flat surface around a hole to accommodate the head of a bolt or a nut. A spot-facing tool is very nearly similar to the counter-bore.

Boring machine

The boring machine is one of the most versatile machine tools used to bore holes in large and heavy parts such as engine frames, steam engine cylinders, machine housing etc. which are practically impossible to hold and rotate in as engine lathe or a drilling machine.