Practice English Speaking&Listening with: Lecture - 18 General Purpose Machine Tool Drills

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Good morning to all of you. Now let us come to our subject Manufacturing Processes - II.

We are continuing Module - 4 which deals with General Purpose Machine Tools and today our

lecture will be dealing with Kinematic system and operations of Drilling machines. It is

a very common machine tool.

Now the Specific Instructional objectives of lecture today: This lecture after completion

will enable the students to identify the basic purposes of use of drilling machines. What

are the main and other purposes of using drilling machines, then classify the different types

of drilling machines available and used. Illustrate the Kinematic system of drilling machine and

explain its working principle. State and visualize the common and other possible operations of

various types of drilling machines.

Now let us start with General purposes of using drilling machines. What are those? Main

purpose of drilling machines is to originate through or blind straight, cylindrical holes

in solid bodies or enlarge existing or pre machined holes. Now let me emphasize to originate

through or blind holes the originate hole that means there is no hole at all in a solid

body. For example, say here is a solid body plate and there is no hole at all, we want

to make a hole like this. Now this hole can be through or this can be part like this,

it is called blind hole and this holes are generally straight straight cylindrical hole

in solid bodies.

Sometimes there may be a small hole existing we want to enlarge the hole that is also done

in drilling machine. So the main purpose of drilling machine is to originate through or

blind holes which will be straight cylindrical in solid bodies and sometime enlarge some

existing holes or some pre machined holes of different diameter. So this can do drilling

on different diameters of varying length or depth in different work materials in different

metals and nonmetals also but expecting very hard and very soft materials like rubber,

polythene etcetera. Now there are many other purposes of using these drilling machines

which are boring, reaming, tapping treads and many others which will be discussed later

on. Now the classification of drilling machines:

The drilling machines normally produce holes through holes and the single straight holes

but even then there are lot of types, different types of drilling machines for different purposes

for different size and shape and all these things. Now let us have a glance on the different

types of drilling machines and then we shall see subsequently the applications of those

drilling machines. Now, the general purpose drilling machines

of common use: Here you see that we are talking about general purpose drilling machines of

common use and why they use? That is first, then we shall discuss on the drilling machines

which are general purpose but used for some specific applications. Now let us have a look

into the common and wide use of general purpose drilling machines. Here you see this one is

a table top small table top small drilling machine.

Now this drilling machine here you see the diagram this is a small drilling machine of

size around say 1 feet 2,3 feet and these are mounted on the table either mounted or

clamped or bolted on the table for rigidity and this spindle. This is the drill which

is mounted on the spindle and the spindle is rotated by belt pulley system and the speed

can be change from say one. There can be 3 speeds low, medium and high speed and the

feed motion of the drill that is the downward motion is imparted manually by operating this

lever either this direction or that direction. So this feeding and withdrawal of the drill

is done manually without any control of the feet rate and this is used normally for small

diameter holes say up to 10 millimeter diameter and power obviously is less because it is

manually operated, maximum half kilowatt or 0.55 kilowatt or may be maximum 1horse power

in case of HP. These are used for repair work or one or two piece job order product and

all these things and small pieces and simple jobs of say softer grades, very hard metals

or odd shapes are not machined in this process and it is not a lot production batch mass

production machine. It is very ordinary piece production general purpose drilling machine.

Next is pillar drilling machine:

Now this looks a pillar drilling machine, it looks like a pillar. Here you see this

is the pillar. This is pillar which has got a circular section that is a tubular section.

So this is not very strong nor very rigid. So this a basically and extension of the table

top machine. It is taller and fitted on the ground mounted on the ground or the floor

or some foundation may be okay. So these are light working machine. The difference between

table top machine and this machine is the wide gap between the drilling machine and

the table also the table can be moved up and down to accommodate larger of different types

of jobs and this table can be swiveled also around this tubular column to accommodate

different types of jobs of different length.

So this is slightly bigger or larger in size, then the table top machine and is obviously

not a mass production lot production type of drilling machine is a very ordinary drilling

machine for one or two pieces of light work. Diameter may vary from 3 to say 20 millimeter,

not beyond that. Power may be say up to 1 point 1 kilowatt and since a long tubular

column job this is not very rigid. So accuracy is not excepted and there may be chances of

vibration and the table is moveable as I told you already. Now what is the next type?

Here is a type called Column drilling machines. This is column drilling machine shown over

here. This is very rigid, ragged machine and quite big size and now lot of work can be

done in this drilling machine and of different diameter of drill, different depth of drill,

and we can machine different job of material, but it is a general purpose drilling machine

with a very low production rate very ordinary production rate. It is not a mass production

or best production machine. The characteristics of this machine is strong, because that the

structure you see is very strong structure. Very powerful machine to allow high speed

drilling by larger diameter drills in say moderately or medium strong materials. It

is rigid for high accuracy and this kind of drill is most common.

We will find in industries these drills are most common. These drills have speed gear

box and feed gear box. The speed gear box and feed gear box are confined with the drilling

head. To enable selection of speed, you can vary the spindle speed and you can also vary

the feed depending upon the requirement and the speed and feed can be changed, quick change

of speed and feed with the help of this speed gear box and feed gear box is possible and

this feed gear box also enables automatic change of feed which is not possible in the

previous drilling machines I discussed wide range of speed and feed are available in the

speed gear box and feed gear box and the blanks, the blanks here is a rigid and large table

the bed on which there may be may not be a table but large bed very strong rigid were

but a simple to very odd and heavy type jobs can also be mounted and comfortably machined.

So this is very common type. What is next type?

It is a radial drilling machine. The radial drilling machine here you see that, this is

the tubular column. This is the tubular column this one but here the tube is very thick and

large diameter and valve thickness is also quite large, this is very rigid okay. This

on that this is the arm here is an arm radial arm which moves up and down manually or it

can powered movement then the drilling head the drilling head here this is called drilling

head which holds the drill spindle here in which the drill is mounted and is subjected

to rotation. The entire head is mounted on the radial arm and this can move inward and

outward from the drill axis. Not only that, as this along with this radial arm the drilling

head moves upward and downward to have large gap between the to drill and job or there

is a stoke length. Not only that further this radial arm can be rotated about the column

rotated about the column, say about 300 degree. Theoretically 360 degree but it can be rotated

300 easily.

Now you understand because of ability of the drilling head to move over up and down over

a long distance inward and outward radially and then swinging around the column. This

allows very large work volume, a large work space were the position were the drill spindle

can be position for doing the work can work on odd shape and size jobs. Even if the job

is very large and odd shape and cannot be mounted on the bed itself it is outside. Suppose

it is so large that some work has to be done elsewhere then the drills the drilling head

will be shifted either upward downward or radially or say swinging and you can do the

work. Again, this spindle this spindle may be actually the versatility of this machine

can be enhanced further by looking into the spindle by having different types of spindle.

The spindle may be vertical and fixed. Only vertical okay and this can be swiveling type

that means this spindle can be rotated. It can be rotated this can be rotated like this

to get some inclined hole.

If one we want to make and tilting is also there. Now this is called swiveling and tilting

is this direction. So the drill can be straight the spindle it can be swiveling type and it

can tilted type that enhances the versatility of the drilling machine. So this drills is

radial drilling machine so used mainly for batch production or piece production of large

jobs or shape jobs. Now CNC drilling machine:

What is CNC? Computer numerical control: It is very modern machine machine tool concept

that since 1970 and 75 onwards, this concept of computer numerical control in machine tools

have come up. You now to cope up with the demand for batch production or what is called

flexible automation. The present trend is batch production which needs flexible automation

that means the automatic system should be capable to change quickly, easily, quickly

and inexpensively to meet the requirement of a new product okay. Normally in fixed automation,

this is very difficult. Now the CNC drill machines different types of machine tools

can be CNC control say lathe CNC lathe, CNC milling machines, CNC drilling machines, CNC

grinding machine, CNC broaching machine. Now drilling machines are also can be CNC. What

are the characteristics of this flexible automation that is speed, feed and movements.

All the movements can be programmed and controlled very easily quickly as simple by simple program

unlike say other kind of conventional machine tools, these machine tools are very rigid

and strong made a strong structure. So the process capability is high. This kind of drills

produces very high accuracy and less vibration. It is programmable, so that you can easily

change from one product to another. This machine tool is really very modern. Came only recently

or very sophisticated and obviously expensive. Now these machines are very much suitable

for piece production and batch production which is the trend of the present and future.

So CNC drilling machines are coming up in that way the very useful machines. Now so

far we talked about the drilling machines which are of very common use of wide application.

Now we shall the drilling machine general purpose but those are used for little more

specific applications. It is not regularly done but sometime and as and when required

it is done and for specific application as and when required. For example, say hand drill

hand drill that means the drill is held in hand. Now this is a portable drilling device.

Now here we see, we cannot call it a drill machine it is actually a small device okay

which can do drilling work and the entire set up shown over here, this is the drilling.

This is drill bit okay. Suppose we want to make a hole in a switch board some holes here.

Now it cannot be taken to the drilling machine nor drilling machine can be taken to this

spot. So into the hole has to be made as a few holes and then this drilling device called

hand drill you know held in a hand normally it is a brought in position and then the hole

is made okay by pressure the feed is given by pressure now what the characteristics.

These are portable number one, these are small so small, it should not be called machine

tool but it can be a device. Now this is high speed. Here the rotation should be high speed

so that the force that come on to the spindle is much less, high speed now this high speed

can be accomplished by high speed electric motor or where there is a chance of you know

hazards or some chemical gases which can burn because of some electrical spark inside if

there are any then, this spindle is rotated by aerator system. Aerator is simply just

like a turbine operated rotated high speed by pressurized air. This is called aerator

and this cannot give high torque but it is at high speed it can rotate and make holes

and this is very necessary for hazardous environment because there is no electric spark or electricity

anywhere okay.

Now the gang drilling machine: now the gang drilling machine from the name itself you

understand that a number of drills, a number of drills are used simultaneously. So this

is little more productive than the conventional machine tools, general purpose drilling machine

I already discussed. The gang drilling machine is a little more productive. It can do work

faster. Now look the principle here instead of one spindle, there are 3 spindles 1, 2and

3. So there are more than 1 2 3 even it can go up to 6 spindles and they will be generally

in a row in a general row and a work is suppose a plate, you place under here and then all

these spindles will move simultaneously okay will move simultaneously and this spindles

can be used in 2 ways progressively and parallel. Parallel means suppose you want to make some

holes of same diameter and it is a long bar. So you place the bar first here under the

drill and you move the drill simultaneously. So you get 3 holes. After that you shift the

bar or the job, so that 3 more holes can be made that means productivity is made 3 times.

Now this can be used in another way that is called progressive. How? Suppose you want

to make a bigger hole of diameter like this. So if this is so big you should you may be

say 40 millimeter or 30 millimeter. So ideally, we should make a small hole, then enlarge

the hole and then finally enlarge the hole in 3 or 4 stages. So this drill will be very

small and this will be little larger and this is the largest final. So you take its bar

to be drilled and then push bring it here. Make the small hole then you push it here.

This will make this hole will come over here that will be enlarged and this will make another

new small hole then, you shift it here then this will make the final larger size and this

small size will be bigger and this one will make another fresh, small hole. So the productivity

will be here also 3 times. But here, we have to remember that for this kind of job one

one jig has to be yet on the job. There should be a plate like called jig has to be used

to keep the location same and the tool guidance and all these things accuracy. So what are

the characteristics? Progressive or parallel drilling is a faster production because 3

drills works simultaneously. Use of a jig is necessity and suitable for batch production

and lot production that is productivity is higher.

Now this is another little high productive drilling machines is called Turret type Drilling

machine. You know turret lathe. Now turret lathes can be horizontal normally some but

sometime the turret lathes are made vertical to save space and particularly when the job

is very large diameter or the chuckle very large diameter, the turret lathes are the

boring mills are made vertical. Here also this shows a drilling machine. Drilling machines

are as such vertical. So this is also vertical axis and there is a turret and the turret

has got number of holes may be 6, 5, 6 up to 10 holes and in to the holes in the holes,

the cutting tools like drills are mounted. Not necessarily there are all drills. There

can be drill some similar tools like a boring tool or a say ream cutter or say counter sinking

tool can be mounted and a job will be mounted on this table. This table will move either

in x direction or in y direction and the entire turret will move vertically up and down along

will the drill.

Now after one tool is used say small drill, then it will go back, then this will rotate

little bit and called indexing and next tool will come in position and do the subsequent

operations. In this way if in any job say 4 or 5 operations are needed say small drill,

then secondary enlargement, thrust enlargement, then boring, then reaming and then finishing

further. So many tools will be used consecutively, so this kind of turret is best suitable for

that purpose. Now the table moment can be you know mechanical or hydraulic or electrohydraulic

or now a days these are driven by numerical control and the entire machine is controlled

by computer. So the whole thing becomes computer numerical control or CNC drilling machine.

So this turret type drilling machine in short is a vertical axis, it possess a turret which

moves up and down along with the cutting tools and it is time to time indexed to bring the

tools in position sequentially and it can be ordinary type or it can be CNC type.

Now Multi-spindle Drilling machine: This is really a special purpose drilling machine,

not exactly special purpose. This is single purpose and combination of single purpose

that is the only drilling and may be slightly different than drilling slightly boring or

counter sinking kind of operation and this is used for large lot production. So this

is in between say batch production and mass production and this is single purpose to special

purpose machine tool. Here multi spindle that is large number of spindles may be you say

up to 10 or 12 spindles all are vertical you know and they are working. Suppose you want

to make number of this is a plate, this is a top view, you want to make number of holes

of different size okay different size at different location say 8holes. It can be of different

shape also circular shape. Now this plate so this will require large number of holes

of different diameter, a different location may be a different depth all right and this

is a large number of pieces have to be produced repeatedly. The same job has to be produced

repeatedly and this is called mass production and this plate has to be mounted first on


First has to be mounted on this table and then there should be a jig. This will be covered

by a jig having some holes already all right according which will be primate. According

to the job to be made for each job type of job there should be a separate jig to be made

which is also resembles the same job. Now if this jig has got number of holes and bushes

through which all the drills you know, they come inside and do the necessary drilling

operation. Now here you see how it is accomplished? There is a central gear. Now this is the motor

which rotates a central gear here. This is a central gear and there some planetary gears

which rotate which are shifted around this circle and this can be rotated about the axis

and this is one those spindles and these spindles again transmit rotation to this spindles through

another set of pair of gears.

So the location the circular angular rotation, position and radial position of the spindles

can be varied by moving this axis and all these are done according to the job to be

done for the location of the holes and this has to be decided and depending upon the diameter

of the hole to be made, different size of drills are mounted on the different spindles

and depending upon the depth of the hole to be made, these drills are used at different

height because the entirely moves simultaneously downward and this will be at different height

so that, the holes of different size different depth can be made and entirely moves up downward

the powered. But sometime, you know this machine is so big that moving the entire head upward

downward may be little difficult and not economy. In that case, the job that is mounted on the

blank along with the fixed jig is moved upward for the feed motion for the cutting action

and after cutting action it is moved down and the spindle head remains in one place

which is quite heavy and large. So this is machine tool, multi spindle machine tool,

were the number of spindles may vary from say 4 to 12 even more and this is used for

mass production or large lot production.

Now Micro drilling machine: now micro drilling machine it is not really micron or micro size.

Micro here means very small drill, very small may be say about maximum 1 feet height or

even say 6 inches 6 inches 1 feet height and this looks like this. Here you can see that,

this is the base. On this is the base okay heavy base which can be directly placed on

the table or it can be grounded on the table to make it is a fixed and then there is a

rod like column and this is a drilling head. This drilling head can be moved up and down

moved up and down with a help of a lever that is necessary for the feed motion. Now here

is the motion is transmitted belt pulley system and normally one or two speeds are available

one high speed, one low speed accomplished by this motor comes through the belt pulley

which has got two pulleys of two groups to give two different speeds but this rotates

at high speed normally because if the speed is increased, then the force on the drill

comes down the thrust force comes down torque and thrust

so speed should be high because it is operated manually and the small jobs of this kinds

of job can be mounted here with the help of small vice and you can do the drilling of

the manually operation. It is just like a table top drilling machine but comes much

smaller size and this is used for very very fine work thus very small work say one or

two pieces have to be make or one hole has to be made. So this is related to repair work

or electrical work, electro fitting work like that.

Now the Deep hole drilling machine: now making deep hole is a problem it is not easy. Now

when we call it a hole a deep. Now the hole has got two dimensions. One is the diameter

and other one is a length length and diameter. So if the length is too large compared to

the diameter, then it is called deep hole say L by d, L is a length and d is a diameter

if L by d ratio exceeds say 10 even 8 we call it deep hole and the lot of problems arise.

Now when we require such kind of deep hole were we need? We deep holes in case of say

barrel of guns, barrel of rifles, sorry and the oil holes in crank shafts oil holes in

bearing housing, then we need very long holes length is very long and high and diameter

is very small. This is called large LYD ratio. Now the main problems in deep hole drilling

as I have already told that, main problem is chip clogging.

Now when we make a deep hole inside a body say this is a drill bit it comes up to this

much then the chips that form here that may be clogged here may be jammed and if the chips

are jammed in the flute, then there will be no cutting action and then the cutting will

be action will be very defective and the cutting flute that is normal used for pulling and

lubrication that may not reach the cutting zone. If the chip gets clogged, so the poor

cutting flute action that hampers cutting action and as a result finally because of

the clogging of the chip and absence of cooling and lubrication and the drill as such is very

slender, very weak slender drill may easily break. So this is very frequent phenomena

or regular phenomena in deep hole drilling. The main problem that chip breaks due to chip

clogging and poor cutting fluid action.

Now these machines are normally so this problem has to be solved okay. How? By chip clogging,

this drills will have to be with a large helix angle large helix angle and the drilling as

to be done intermittently first you just proceed little bit say 1 centimeter you withdraw the

drill, clean all the chips and all these things then you again push it again lift it then

you again push it again lift it. So you keep on cleaning the chips do not allow the chips

to clog. Secondly the cutting flute as to be applied profusely all right and not only

that under pressure and sometime to reach the cutting fluid at the end drill tip. This

has to go through the drill is made hollow through the hole pressurized flute is pass

through to reach the cutting zone. So then this problem will be overcome.

Anyway these drilling machines are normally horizontal; horizontal axis because the hole

is weak, the drill is big and the whole spindle is big. So if it is vertical, then it will

be too slender the whole machine will be too slender and that means the lack of rigidity.

So accuracy analysis will be lost. So these are made horizontal. High speed spindle to

reduce the cutting force because if the force is large, this slender drill may buckle or

break. High rigidity so that is no chance of any vibration or buckling tool guide since

the guide tool is very long and slender some the tool has to be guided the tool has to

be guided through the guide the tool will move so that, this lateral movement is prevented.

Pressurized cutting fluid through the drill one or two holes are made through the drill

through that the hole is the while is passed and both ordinary and CNC machines are visible.

But nowadays, these deep hole drill are converted or made in with CNC control for accuracy and


So in defense, they use lot of say CNC deep hole drilling machines for boring and drilling

the guns barrels or antiaircraft, gun rifles and so on. Now let us come to very important

aspect of lecture today that is Kinematic system. Just now you have heard, so many types

of drilling machines, very small to very large. Manual to automatic control and up to CNC

control, very resilient to very rigid okay horizontal vertical drilling with the different

types of drills and diameter but the Kinematic diagram is more or less say in say where there

is feed gear box and speed gear box. Here you can see, this is the speed gear box and

feed gear box that means the

speed and feed or can be changed frequently depending upon the requirement and feed can

be changed or adopted automatically like radial drilling machine, column drilling machine

and automatic drilling machine turret head and so on. So this is the Kinematic structure

of very common type of drilling machines, basically column type drilling machine and

to some extent radial drilling machine. Now what are there inside? Now the Kinematic system,

the Kinematic system as i told you earlier also in our previous lectures that is, this

arrangement the Kinematic system of when a machine or machine tool deals with only motions.

Transfer of motion and transformation of motion like say from rotation to rotation, rotation

to translation, translation to rotation, rotation to oscillation and so on and transfer of motion

from one point to another point from the source to the drill cutting point. So this is called

Kinematic system. Now let us go into this Kinematic system.

Now this is the drilling machine okay. This is column drilling machine. What is the main

part? This is a power source say motor only motor. We are excluding at this moment, we

are not discussing at this moment this lubrication or other kind of drive only power drive that

is the single motor. This is the cutting tool drill. Here is only machine tool where both

the cutting motion and feed motion are given to the tool. So the drill bit here that is

made to rotate and same drill is made to move down. The work piece the work piece remains

completely stationary in such kind of drill now. So this drill is mounted in a drill socket

the drill is mounted in a drill socket here. The drill socket is fitted into this spindle,

this is called the drilling machine spindle which has got a long bar at the tail end which

is plain, I am coming to that why now this spindle is partially hollow here? So the drill

is or the drill socket is fitted into this taper hole.

Now the drill spindle has to be rotated to rotate the drill where from the drill spindle

achieves or attains the motion? The drill spindle is connected to the motor through

a gear box called speed gear box. This is a speed gear box okay, where the speed is

not only transferred or transmitted transmitted to the drill. It is also splitted, motor rotates

are the constant RPM. But drill may require different RPM very slow, very large, or very

high depending upon the work material, tool material, tool material, tool diameter, machine

tool condition. So there is a provision that is called speed gear box which enables splitting

or reducing or increase the motor speed to a high or low value and with the help of some

cluster gears. So this is how the spindle is made to rotate. Now this is the enlarged

view of the speed gear box. So the power comes from the motor, this is a reversal mechanism

which really converts say the rotating motion from clockwise to anticlockwise or may be

anticlockwise to clockwise.

So when we need clockwise motion, so the clutch will be operating in this direction. When

we need say anticlockwise when say for producing threads by tapping, we need this anticlockwise

rotation. So, the clutch will be moved and we can get clockwise and anticlockwise motion.

Now the speed comes to first shaft. Now through these gears with split to tube, two then again

it is splitted into two. Now again finally splitted into three: So how many speeds we

get. So 2 into 2 into 3. So this is a 12 speed gear box and the power comes from the final

shift through the pair of gears through the gears this spindle goes. Now the spindle is

plane why because this spindle will move up and down.

So this will move up and down along while it is rotating, so this spine shaft will allow

the movement of the spindle up and down through the gear without hampering the transmission

of rotation. So transmission of rotation will continue, but the drill spindle can be moved

up and down through this gear with the help of this plane then the feed motion, the drill

has to be moved up and down. This is actually done this spindle is mounted in a quill or

barrel. These are box type which moves up and down okay and this has got a rack on its

wall and on the rack, there is a pinion when the pinion is mounted on the shaft. When the

shaft is rotated the pin is rotated clockwise or anticlockwise along accordingly this quill

along with this spindle will move up or down okay. So this shaft is rotated by another

worm wheel that is rotated by one worm and that can be rotated a wheel manually.

So by operating this wheel manually, you can rotate this pinion and make this spindle move

up and down. So manual drilling is possible. Now if you want it to automatic, then the

speed comes from you have to use this feed gear box. This is the feed gear box. This

is the feed gear box okay. Now explaining; the power is coming from this spindle final

a spindle shaft through a reduction because feed motion is very slow. It is brought to

the shaft through a feed reduction mechanism. So that is called this can enable the movement

upward or movement downward that means the pinion has to be rotated upward sorry clockwise

or anticlockwise to move this spindle downward and upward. So to change this direction of

rotation of this pinion, this clutch is operated, this system is operated, this clutch is operated.

This clutch can be moved either this way or that way that will make this spindle rotate

either clockwise or anticlockwise.

Now that will be transmitted to this shaft in this two that will be again splitted into

three. So this shaft can be rotated at any one of the 6 speeds and that will convert

into feeds. Now if you engage this clutch, now this rotation reduce rotation will be

transmitted to this pinion through this worm wheel and this worm okay and this will be

done then defined. Now you can change this feed by operating the cluster shift in the

cluster gears. So you can have any one of the 6 different feeds okay and this is a bed

on which the job is clamped either in a vice or directly by clamping and rigidly mounted

and this is a column which is very rigid and this is base of the drilling machine and the

base is fitted, clamped on the foundation concrete foundation. So this is the Kinematic

structure of drilling machines. Now it varies machine to machine or manufacture to manufacture.

Here we have shown 12 speed gear 12 speed gear box that means the spindle can rotate

at 12 different speeds, but they are drilling machines if wanted it can be 18 speed it can

be 24 speed. Similarly the feeds can be increased from 6 to 8 to 12 and so on by having different

cluster gears.

Now the application of drilling machines applications or operations the various kinds of operations

or applications possible in drilling machine. Now this is very important because those who

will use the drilling machine they should know about it. Now the drilling through the

primary is drilling through or blind holes. Now what is I am reminding you that, if you

want to make a hole suppose this is a rod, it is plate or say block, you want to make

a hole up to this much by a drill okay. Then this is called blind hole. If you want to

make full length up to bottom then this is called through hole. So drilling machines

are mainly used for drilling holes all right which can be through which can be blind and

this is the most common application of drilling machines and this whole again this whole as

I have shown this is straight hole okay.

Now this can be taper, this can be taper hole but taper hole is very rare very occasional;

now by it has done it as to be done by special drill but straight hole is most common and

sometime stepped hole is also made. Stepped hole means say this is the work surface, we

make a one diameter hole then another diameter, then another diameter final. So the diameters

are varying at different position of the portion of the hole okay. This is called stepped hole

and sometime I already told this hole is made very deep okay of the small diameter but very

large depth. So this is a various kind of holes. Now in addition to making holes what

else can be done? Centering- that is done for making small holes and the job to be turn

in the lathe. Boring- for enlargement of holes, then counterboring and countersinking. This

will be discussed more detail, then Reaming- for finishing by reamer and tapping for cutting

threads, internal threads in nuts and so on. So all these things will be discussed now:

Classification of drills and drilling operations: For different drilling operations, different

types of drills are obviously required. Now the drills have to be classified, different

types you know few dozen types of drills are available. How do you classify? This can be

this classification can be made in different aspects according to size according to length

according to aspect ratio according to material and so on. Now let us go in systematically.

According to the classification of drills according to material now the drills can be

made of different material. High speed steel okay. You know the high speed steel was introduced

in 1905 by F.W.Taylor which contains about 18 percent tungsten and 4 percent chromium

vanadium. Sometimes little bit cobalt is also is added and later on as high speed steel

and these are very tough and strong. Since drills are very slender tool and geometry

is very complex.

So high speed steel with its toughness, formability and strength tensile strength and transverse

obturator strength are mostly appropriate. So most of the drills or the tools those are

used in drilling machines are made of high speed steel. Even today, through the cutting

speed is not that high possible then comes cemented carbides which are produced powder

metallurgically this carbides can be uncoated can be coated tools. The diamond-sometime

for making very small holes in exotic materials diamond is used where other tools cannot do

work, because of hardness of the material or special to the material and size of the

hole etcetera. So diamond is very occasional very rarely used only for very special application

like very find holes or for very exotic material. But diamonds again I remind you that, diamond

tools are never used for machining steels like material then the diamond will be graphitized.

Now we can classify the drills according to size. Not very clear cut demarcation is available

or used but anyway there is a generally people call it micro micro drill. What is the micro

drill or micro drilling? When the size of the driller size of the hole will be around

25 five micron to 500 micron 500 micron means I remind you the half of millimeter. Now you

can imagine what is the size 25 micron to that small size drilling is possible and is

called micro drilling for that special drills called micro drills are available made available.

Moderate-that is 3 to 25 millimeter really most of the drilling work we do in industries,

they are within 3 to 25 millimeter. So this is the most widely used region and with this

size of drills are used in plenty in the work shop and market Large - Occasionally we drill

large holes. Normally if the hole is too large say bearing or something or bearing housing

have to be made then hole is made by drilling originated then it is enlarged by boring operation.

So drilling if to be done to a large extent then maximum 40 millimeter occasionally may

be 45 millimeter some manufacturers or some users may be using but normally 25 to 40 millimeter.

We call it large diameter and this means that there will large force large torque some machine

tool that is very powerful rigid all right.

So this is not a mass production machine. Now the classification according to number

of flutes. Now this is you know the drill has got fluted the drill this is a drill this

is actual view, this is one flute and this is another flute and this flute continuous

along this flute continuous along this flute continuous helically sorry and then how many

flutes are there. The flutes actually provided for removal of the chip or because this cutting

edge will produce a chip how this will be removed from the hole through this cavity

or flute. These chips will pass out and secondly the flute angle the helix angle the flute

angle that governs the rake angle of cutting tool. Now according to number of flutes two

fluted most common very ideal and most common single flute very rare this is used to make

the drill bit very strong and rigid. For example; gun drill, deep hole drill, crank shaft hole

drill etcetera. Sometimes 3 or 4 flutes are also used. These are called slot drill okay.

Slot drills to reduce the load path tooth sometime this slot drills are make or use

for making holes will flat end like this normal drills make a tip or a cone type but this

makes a flat. Sometimes this slot drills are also used to make some slots this slot drills

look like sometime to some extent end mill cutter.

According to helix angle of the flutes, normally it varies from 20 degree to 35 degree. I already

told that this helix angle really represents also governs the rake angle. You know for

cutting ductile material with a long chip large rake angle is necessary. So the helix

angle should also very large. So this will not only enable very good removal of the chip,

but also help reduce the cutting force by virtue of large large helix angle. The usual

helix angle up to 35 degree. What is the large helix angle 45 degree up to 60 degrees. These

are used suitable for long drills for deep hole drilling in soft materials or yes or

for making holes in very soft material like aluminium, copper other alloys. So the helix

angle, large helix angle means lesser force. But if we increase the helix angle, the rake

angle will increase. Chip disposal will be better but the strength of the drill will

decrease. So this will be used for long drills and soft materials small helix where large

helix is prohibited for harder material. When you make hard machine harder materials, so

the core of the drill as to be made harder strong and that means this small helix will

be there zero helix. Yes when the work piece is really very very hard or we want to do

spade drilling. Spade drilling means you know this is the rod and then this is the drill

bit is a plate like is a plate like okay.

This is the spade drill. Now the spade drills are used for large production and harder materials.

Sometimes micro drill for very small drills also; this helix angle is avoided because

the micro drills are such very small in diameter and weak. So they have to be retained strong

by zero helix. Next is according to length of diameter. length to diameter ratio, L by

d ratio okay general normally L by d ratio should be within 5 to 10 that is maintained

okay, neither very small nor very large. If the L by d ratio is too large, the drill becomes

weak. If it is too small, the chip removal will be difficult. Long drills as I told you

that this L by d ratio for deep holes. There the ratio should be more than 10. It can go

up to 25 the ratio, short drills where the L by d ratio will be very small say about

say centre drills like centre drills 2 or 3. According to the shank type, that straight

shank and taper shank, sometime the shank of the drill is tapered to or sometime it

is straight. When it is straight shank, then it is held in the chuck. Otherwise it is socket

or directly into the spindle.

Now the classification of drills: again according to specific use this one shows a specific

use this is a centered drill. This is called center drill very short drill and this makes

this hole this makes the hole necessary they provide it at the end of the job to be turned

and this hole is used to support this center which has to be mounted into the headstock

or tailstock. This is called centered drill and one taper has to be made here, then comes

you know step drill. So if you want to make step drill say one diameter, the hole has

to be diameter has to be changed say up to this much. The diameter is this much and then

diameter is reduced we can use as the step drill or subland drill. This is the drill

which makes you know in one stroke to two type.

Then half round drill; half round this is half round drill. This is called half round

drill this one half round drill, then gun drill. This is a gun drill and crank shaft

drill this one. These are basically long drills where L by d ratio is very large and only

one cutting edge is there, one flute is there and there may be two flutes. But the base

is very strong and this is called half round various types of drills. Now this is a trepanning

tool. Now what is trepanning tool? is a pipe like cutting tool is a pipe like cutting tool.

Suppose you want to remove this material. This is hole has to be made. So what you do?

You take a cutter pipe like okay. A pipe like cutter and then just gone cutting edges here.

So when this will rotate this will remove material only from this region only from this

material remove and this central material remains un-machined. So you can get an extra

core. So this is one way of removal of making large hole by removing small material but

this is feasible for softer material. So this is one piratical type of machine of such the

cutter called trepanning tool.

Now further use of drilling machines other than general purpose. So this is called slot

drilling and slotting as I told you already, the boring after drilling enlargement of hole

by putting a boring tool in the drill spindle instead of a drill, you can do boring. You

can change the diameter of the both boring tool. Counter boring, this is the example

of counter boring. So you made a hole then you enlarge the diameter at that top end to

accommodate say then bolt head or some nut. Sometime it is tapered to put some screw and

is called countersinking. Now spot facing; here is a surface at the top of the hole which

as to be flattened. So this is called you know spot facing operation.

Then comes Reaming: Reaming means finishing. There are various reamers which looks like

into some extent drills but there this has got a taper cone. These are just like long

milling cutters and they are fitted into the drill after drilling because drilling does

not give very good high accuracy and a finish. So this has to finished sometime. Even after

boring you do not get good enough say surface finish an accuracy. Then the finishing work

directly after drilling or drilling and then subsequently boring finished by this cutters

called reamers a rod like and they have got edges or ribs which are nothing but cutting

edges. This is a small one. There are different types straight fluted rose reamers, this one.

Straight fluted chucking reamer held in chucks slightly bigger straight fluted taper reamers

is a slightly taper to finish the taper holes for taper gibs and all these things and this

straight fluted hand reamer operated manually in a lathe sometime and expansion reamers

where this diameter can be slightly adjusted within few microns. Shell reamer- this is

a basic tool on which the reamer part can be removed and fitted. So this is engaged

and this is engaged of different diameter.

You can choose it and fix it and the last one is adjustable insert blade. The blades

there are separate blades available in the strips which are fitted into the groves provided

into the slot on to the body and this can help, enable, change in the diameter or replacement

of the worn-out cutting tools. Now next is tapping. The tapping means cutting internal

thread say nuts, the small nuts have got say the internal threads. How this thread will

be made? You can make it in a lathe all right you make in drilling machine. If you want

to make it in large lot production or mass production, then this has to be done in a

drilling machine of course with the help of some drilling the tapping attachment. The

tapping attachment is fitted first into the drill spindle and then the tap tool is fitted

at the end.

Now here we need two motions during cutting motion the rotation and translation and during

internal motion it should rotate in the opposite direction and gradually come up, the tapping

attachment enables all this moments. So this tapping is accomplished in a drilling machine

but with of an attachment. Similarly by using different types of attachments you can produce

different types of jobs. There are a lot of examples. If there is real need or if there

is a challenge then various kinds of job can be done even in ordinary drilling machines.

But you have to use appropriate jig fixture, then some attachment like tapping attachment

and different types of tools and so on. So these drilling machines are really quire versatile.

It can do many many types of work from very job order production to mass production, to

very less precision to very precision for small diameter to large diameter for very

soft material tool hard material, for very short length to high length. Next day we shall

discuss on milling machine. Thank you.

The Description of Lecture - 18 General Purpose Machine Tool Drills