Drilling, Milling and Reciprocating Machine Tools

• Drilling machine consists of a spindle which imparts rotary motion to the drilling tool, a mechanism for feeding the tool into the work, a table on which the work rests and a frame.

• It is considered as a single purpose machine tool since its chief function is to make holes.

Drilling machine

Classification of Drilling Machines:

• Drilling machines are classified according to the construction and the work performed as follows:

I. Portable drilling machineII. Sensitive drilling machineIII.Upright or column drilling machineIV. Radial drilling machineV. Gang drilling machineVI.Multi-spindle drilling machineVII.Vertical turret type drilling machineVIII.Automatic drilling machineIX.Deep-hole drilling machine etc.

Specification of a Drilling Machine:

a. Portable drilling machine is specified by the maximum diameter of drill which can be held.

b. Sensitive and upright drilling machines are specified by the diameter of the largest work piece that can be drilled.

c. The radial drilling machine is specified by the length of the arm and column diameter.

d. Multiple spindle drilling machine is specified by the drilling area, the size and the number of holes a machine can drill.

Drilling machine operation:

• Drilling • Reaming• Boring• Counter boring• Counter sinking• Spot facing• Tapping

Reaming :

• It is a process of smoothing the surface of drilled holes with a tool.• Tool is called as reamer.• Initially a hole is drilled slightly smaller in size.• Drill is replaced by reamer.• Speed is reduced to half that of the drilling.

Boring:

• It is process carried on a drilling machine to increase the size of an already drilled hole.

• Initially a hole is drilled to the nearest size and using a boring tool the size of the hole is increased.

Counter boring:

• This process involves increasing the size of a hole at only one end.

• Cutting tool will have a small cylindrical portion called pilot.• Cutting speed = two-thirds of the drilling speed for the same

hole.

Counter sinking:

• This is an operation of making the end of a hole into a conical shape.

• Cutting speed = half of the cutting speed of drilling for same hole.

Spot facing:

• It is a finishing operation to produce flat round surface usually around a drilled hole, for proper seating of bolt head or nut.

• It is done using a special spot facing tool.

Tapping :

• Process of cutting internal threads with a thread tool called as tap.

• Tap is a fluted threaded tool used for cutting internal thread• Cutting speed is very slow.

Drilling:

• Drilling is a process of making hole in an object by forcing a rotating tool called Drill.

• The cutting tool used in drilling is commonly known as a twist drill.

Elements of a Twist Drill:

• Body: it is the part of the drill that is fluted and relieved.• Shank: it is the part held in the holding device.• Dead centre: the dead centre or chisel edge of the drill is

the sharp edge at the extreme tip end of the drill.• Lip: lip or cutting edge formed by the intersection of the

flank and face. Both the lips of the drill should be equal length and should be at the same angle of inclination with the drill.

• Flank: flank is the surface on a drill point which extends behind the lip to the flowing flute.

• Chisel edge corner: the corner formed by the intersection of a lip and the chisel edge is called chisel edge corner.

• Flutes: the grooves in the body of the drill which provides lips.

Milling Machine• Milling is a process in which a rotating multi-tooth cutter removes

material while traveling along various axes with respect to the workpiece.

MILLING MACHINE OPERATIONS:Following different operations can be performed on a milling machine :• Plain milling operation• Face milling operation• Side milling operation• Straddle milling operation• Angular milling operation• Gang milling operation• Form milling operation• Profile milling operation• End milling operation• Saw milling operation• Slot milling operation• Gear cutting operation• Helical milling operation• Cam milling operation• Thread milling operation

Principal Parts:

Base: It provides rest for all parts of milling machine including column. It is made of grey iron by casting.Column: It is a type of rigid vertical long box. It houses driving mechanism of spindle, table, knee is also fixed to the guide ways of column.Knee: Knee can be adjusted at a height on the column. It houses the feed mechanism of the table and other controls.Saddle: Saddle is placed at the top of the knee. Saddle provides guide ways for the movement of the table.Table: Table rests on the saddle. It consists of „T‟ shaped slots for clamping the workpiece. Movements of the table (feed motions) are given in very controlled manner be lead screw.

Overhanging Arm: Overhanging arm is mounted on the column and serves a bearing support for the arbor. This arm is adjustable so that the bearing support may be provided near to the milling cutter. There can be more than one bearing supports to the arbor.Arbor: It holds rotating milling cutters rigidly and mounted on the spindle. Sometimes arbor is supported at maximum distance from support of overhanging arm like a cantilever, it is called stub arbor. Locking provisions are provided in the arbor assembly to ensure its reliability.Front Brace: Front base is used to adjust the relative position of knee and overhanging arm. It is also an extra support fixed between the knee and overhanging arm for rigidity.Spindle: Spindle is projected from the column face and provided with a tapered hole to accommodate the arbor. Performance of a milling machine depends on the accuracy, strength and rigidity of the spindle. Spindle also transfer the motive power to arbor through belt or gear from column.

Types of Milling Machines:

The varieties of milling machines available are:I. Knee and Column Type

a. Horizontalb. Verticalc. Universald. Turret type

II. Production (Bed) typea. Simplexb. Duplexc. Triplex

III. Plano millersIV. Special type

a. Rotary tableb. Drum typec. Copy millingd. Key way milling machinese. Spline shaft milling machines

Universal Milling Machine:

• A universal milling machine is named so as it is used to do a large variety of operations.

• The distinguishing feature of this milling machine is it table which is mounted on a circular swiveling base which has degree graduations.

• The table can be swiveled to any angle on either side of normal position.

• Helical milling operation is possible on universal milling machine as its table can be fed to cutter at an angle.

• Provision of large number of auxiliaries like dividing head, vertical milling attachments, rotary table, etc. make it suitable for wide variety of operations.

Indexing:

• The operation of rotating the job through a required angle between two successive cuts is termed as indexing.

• This is accomplished with the help of a milling attachment known as dividing head, which is an accessory to the milling machine.

• It helps to divide the job periphery into a number of equal division.

Indexing or dividing head:

• To rotate a job through required angle , one needs (a) a device to rotate the job and (b) a source which can ensure that the job has been rotated through the desired angle.

• In dividing head, the first requirement is met by an index-crank and second by index plate.

• The index-plate has a number of holes arranged concentrically, so that each circle has a number of holes equally spaced.

• The rotation of crank is transmitted through a gear to the job .

• The ratio of the crank and the shaft on which job is mounted is 40 : 1, i.e., when the index plate makes 40 revolutions, the job makes one revolution.

Common methods of indexing:

There are five methods of indexing:

1.Direct indexing2.Simple or plain indexing3.Compound indexing4.Differential indexing5.Angular indexing

DIRECT INDEXING:

• The dividing head has an index plate , fitted directly on the spindle.

• The intermediate use of worm and worm-wheel is avoided.• The index plate has 24 holes.• Numbers that can be divided into 24 can be indexed in this

manner.• To find the number of holes to move the index plate, divide 24

by the number of divisions required.• Number of holes to move = 24/ N

Where,N = required number of divisionsExample: Indexing for a hexagon head bolt:

because a hexagon head has six flats,

Simple or plane indexing:

• Indexing plate with varying number of holes are used to increase the range of indexing.

• The index plate is fixed in position by a pin called lock pin.• The spindle is then rotated by rotating the handle (index crank)

which is keyed to the worm-shaft.• The following relation is used for simple indexing : T= 40/N ;

where N is the required number of division on the job periphery.• For example, to index for the machining of a hexagon (N = 6):

Thus it required 6 full turns with 10 holes in a 15-hole circleor,12 holes in a 18-hole circle

Compound indexing:

• The principle of operation of compound indexing is the same as that of the simple indexing.

• The only difference is that compound indexing uses two different circles of one plate.

• The principle of compound indexing is to obtain the required division in two stages:

i. By rotating the crank or handle in usual way keeping the index plate fixed with lock pin.

ii. By releasing the back pin (lock pin) and then rotating the index plate with the handle.

• For example, if a 27 teeth gear is to cut, then T= 40/27; the rotation required for one tooth spacing is 40/27 which may be written as 2/3+22/27 or 12/18+22/27.

• So for each tooth, the worm will be rotated by 12 holes of 18 hole circle with the help of the crank and then the index plate is rotated by 22 holes of the 27 hole circle.

Angular indexing:

• Instead of rotating the job through certain division on its periphery, sometimes it may be needed to rotate the job through certain angle.

• Angular indexing is used for this purpose.• Since the crank and spindle ratio is 40:1 so when the crank moves

1 revolution, the spindle or job moves through 1/40 of revolution.• This means the job will revolve through an angular movement of 9

degree.• If it is desired to index a job by 35 degree, then the indexing head

movement required to perform the operation will be = 35/9=3+8/9=3+24/27

• That is the crank must turned three complete revolutions plus 24 holes in the 27 holes circle.

Differential Indexing:

• The term differential is used because the needed division is obtained by a combination of two movements:

1. The simple indexing movement of the index crank, and2. The movement of the index plate itself,

• These two movements happen at the same time with a differential in their movement relationship.

• The index-head spindle and the index plate are connected by a train of gears so that the index plate will turn either in the same direction as the movement of the crank or in the opposite direction.

• For making the necessary calculations and to find the change of gears to be placed between the spindle and the worm shaft, use the following relation:

Driver/Driven = (n-N) *40/ᴫCrank movement = T = 40 / n

Where, n is a number slightly greater or less than N• The difference of N and n causes the index plate to rotate itself in a proper

direction relative to crank.• If (n – N) is positive, the index plate will rotate in the direction in which crank is

rotated.• If (n – N) is negative, the index plate will rotate in opposite direction to that of

crank.

Shaper Machine