DRILL AND CUTTING SPEED & FEED

May 30, 2020

INTRODUCTION:-

i)- Everyday in a workshop to do holes is required so for that cutting tool is used known as drill.

ii)- Tool used to make hole is called drill.

iii)- It is made by high carbon steel or alloy steel.

iv)- The drill bit is rotated with a downward pressure causing the tool to penetrate into the material. The process for making hole in a job is called drilling operation.

v)- There are three types of drills:- a)- Flat drill, b)- Straight fluted drill, c)- Twist fluted drill.

a)- Flat drill:-

i)- It is made on high carbon steel and can be any size as per required.

ii)- Its cutting angle is 90degree. and clearance angle is 30degree.

iii)- It is mostly used in carpentry work.

b)- Straight fluted drill:-

i)- It is made on high carbon steel(HCS) and high speed steel(HSS).

ii)- It is used for Rough drilling.

iii)- The body of drill has two straight parallel flutes cut.

c)- Twist fluted drill:-

i)- It is modern type of drill bit is mostly used in every engineering workshop.

ii)- It is made by high carbon steel, high speed steel & alloy steel.

iii)- Its one end has cutting edge and spril flutes cut on its body.

iv)- This looks like a twist so it is called twist drill bit.

v)- The main advantage of these flutes are cutting of chips come out easily and coolant reaches to cutting point also easily.

vi)- Its cutting point angle is 118 degree.

vii)- According to Indian standards, three types of drills are used for drilling various materials.

a)- Type N - For normal low carbon steel.

b)- Type H - For hard and tenacious materials.

c)- Types S - For soft and tough materials.

viii)- Twist drills are designated by the a)- Diameter, b)- Tool type, c)- Material.

for Example:- Twist drill 9.50 - H - IS5101 - HS

where H = tool type, IS5101 = IS Number, HS = tool material, 9.5 = diameter of the drill.

NOTE:- If the tool type is not indicated in the designation, it should be taken as type ‘N’ tool.

Parts of a Drill:-

a)- Point, Shank, b)-Tang, Body, c)- Flutes, d)- Land/Margin, e)- Body clearance, f)- web.

a)- Point:- i)- The cone shaped end which does the cutting is called the point.
ii)- It consists of a dead center, lips or cutting edges, and a heel.
b)- Shank:-i) This is the driving end of the drill which is fitted on to the machine.
ii)- Shanks are of two types:- a)- Taper shank used for larger diameter drills, b)- Straight shank used for smaller diameter drill.
c)- Tang:- i)- This is a part of the taper shank drill which fits into the slot of the drilling machine spindle.
d)- Body:- i)-The portion between the point and the shank is called the body of a drill. ii)- The parts of the body are flute, land/margin, body clearance and web.
e)- Flutes:- i)- Flutes are the spiral grooves which run to the length of the drill.
ii)- The flutes help To a)- form the cutting edges , b)- To curl the chips and allow these to come out , c)- The coolant to flow to the cutting edge.
f)- land/margin:-i)- The land/margin is the narrow strip which extends to the entire length of the flutes.
ii)- The diameter of the drill is measured across the land/ margin.
g)- Body clearance:- i)- Body clearance is the part of the body which is reduced in diameter to cut down the friction between the drill and the hole being drilled.
h)- Web:- i)- Web is the metal column which separates the flutes.
ii)- It gradually increases in thickness towards the shank.
Drill angles:-
They are different angles for different purposes. They are listed below.Point angle, helix angle, rake angle, clearance angle and chisel edge angle.
Drill-holding devices:-
i)- The common drill-holding devices are a)- drill chucks, b)- sleeves, c)-sockets
Drill chucks:- i)- Straight shank drills are held in drill chucks. For fixing and removing drills, the chucks are provided either with a pinion and key or a knurled ring.
ii)- The drill chucks are held on the machine spindle by means of an arbor (Fig 1B) fitted on the drill chuck.
iii)- Drill chucks are made from special alloy steel .
Taper sleeves and sockets:- i)- Taper shank drills have a Morse taper.
ii)- Due to this reason Morse tapers are called self-holding tapers.
iii)- The drills are provided with five different sizes of Morse tapers, and are numbered from MT 1 to MT 5.
iv)- When the drill taper shank is bigger than the machine spindle, taper sockets are used.
v)- Use a drift to remove drills and sockets from the machine spindle.
vi)- Drill sleeves are made from case hardened steel.
Cutting speed:-
i)- Cutting speed is the speed at which the cutting edge passes over the material while cutting, and is expressed in metres per minute.
ii)- The selection of cutting speed for drilling depends on the materials to be drilled,and the tool material.
iii)- Cutting speed formula is πdn/1000 (n = r.p.m. , v = Cutting speed in m/min. , d = diameter of the drill in mm. π = 3.14)
Feed in drilling:-
i)- Feed is the distance (X) a drill advances into the work in one complete rotation. (Example - 0.040 mm/ rev).
ii)- Feed is expressed in hundredths of a millimetre.
iii)- The rate of feed is dependent up on a number of factors.
a)- The finish required, b)- Type of drill (drill material), c)- Material to be drilled