Cnc

1. CNC
DRILLING&MILLING
1
OPERATIONS

2. Agenda
 Tools Nomenclature
 Drilling Operations
 Drilling materials
 Drilling definition & machining calculation.
 Milling Operations
 Types of Mills
 Milling Operations
 Parameters
 Milling Calculations
2

3. Tool Nomenclature 3

4. Types of Operations:
 Pilot (Center) Drill
 Drilling
 Boring
 Counter Boring
 Reaming
 Counter Sinking
 Tapping
4

5. CENTER DRILLS
Purpose: To center drill stock on the lathe, and to
accurately start holes on the mill.
Available drill sizes
5/64, 7/64
#s 1-4, 5, 8
5

6. Drilling 6
 Creates a round hole in a
work part.
 Contrasts with boring
which can only enlarge an
existing hole is called a drill
or drill bit.
 Customarily performed on
a drill press, but can be
done on a vertical mill and
on a lathe
 Drill holes from 1.5 to
15mm
 Drill holes up to 50mm Figure : Drilling

7. Through Holes vs. Blind
Holes
7
Through-holes - drill exits the opposite side of work
Blind-holes – drill does not exit work on opposite side
Figure - Two hole types: (a) through-hole, and (b) blind hole

8. Boring 8
Provides a
stepped hole, in
which a larger
diameter follows a
smaller diameter
partially into the
hole
Figure : counter-boring

9. Counter Boring 9
A counter-bore hole is
usually used when the
head of a fastener, such
as a hex head, socket
head caps.
It is required to be flush
with or below the level
of a workpiece's
surface.

10. Reaming 10
Used to slightly
enlarge a hole,
provide better
tolerance on
diameter, and
improve surface
finish
Figure : Reaming

11. Countersinking 11
Enlarge and bevel
the rim of (a drilled
hole)
so that a screw, nail,
or bolt can be
inserted flush with
the surface.
Figure : countersinking

12. Tapping 12
Used to provide
internal screw
threads on an
existing hole
The tool is
called a tap
Figure Tapping

13. 13
Drilling And Drills
Types of drills
– Twist drill: most
common drill
– Step drill:
produces holes
of two or more
different
diameters
– Core drill: used
to make an
existing hole
bigger

14. 14Drilling Materials:
The two most common types are
1. HSS drill
- Low cost
2. Carbide- tipped drills
- high production and in CNC machines
Other types :
• Solid Carbide drill
• TiN coated drills
• carbide coated masonry drills
• parabolic drills, split point drill.

15. 15
Cutting Speed (v):-
It’s the peripheral speed of the drill
v = *D*N where
D = diameter of the drill in m
N = Speed of rotation in rpm
Feed Rate (f):-
It’s the movement of drill along the axis (rpm)
Depth of cut(d):-
The distance from the machined surface to the drill axis
d = D / 2
Material Removal Rate:-
It’s the volume of material removed by the drill per unit time
MRR = ( D2 / 4) * f * N mm3 / min
Machining Time (T) :-
It depends upon the length (l) of the hole to be drilled , to the
Speed (N) and feed (f) of the drill
t = L / f N min
Definitions

16. Machining Calculations:
Drilling
 Spindle Speed - N (rpm)
 v = cutting speed
 D = tool diameter
 Feed Rate - fr (mm/min -or- in/min)
 f = feed per rev
 Machining Time - Tm (min)
 Through Hole :
 t = thickness
  = tip angle
 Blind Hole :
 d = depth
 Mat’l Removal Rate - MRR (mm3/min -or- in3/min)
16
Dπ
v
N 
r
m
f
d
T 
Nffr 
4
2
fD
MRR
π

  
r
2
θ
2
1
m
f
-90tanDt
T



17. Milling
 Machining operation in which work is feed past a
rotating tool with multiple cutting edges
 Axis of tool rotation is perpendicular to feed direction
 Usually creates a planar surface; other geometries possible
either by cutter path or cutter shape
 Other considerations and terms:
 Milling is an interrupted cutting operation
 Cutting tool called a milling cutter, cutting edges called "teeth"
 Machine tool called a milling machine
17

18. 18TYPES OF MILLING OPERATIONS
 Face Milling
 Slab Milling
 Profile Milling
 End Milling
 Slotting
 Pocket Milling
 Surface Milling

19. Vertical Mill
Vertical knee and column milling machine

20. CNC Vertical Mill 19
Spindle Speed
Saddle Table
Knee
ColumnHead

21. CNC Vertical Mill: Axes &
Tools
21
Spindle
+ Z-axis
+ X-axis
– Y-axis
Tool Holder
Cutter
Alternate
Tools
(in quick-
change
magazine)
Air Vise

22. Conventional Face Milling 22
Cutter overhangs work on
both sides
Figure : conventional face
milling

23. Slab Milling 23
The basic form
of peripheral
milling in which
the cutter width
extends beyond
the work-piece
on both sides
Figure : slab milling

24. Slotting 24
Width of cutter is
less than work-
piece width,
creating a slot in
the work
Figure : slotting

25. End Milling 25
Cutter diameter is less
than work width, so a
slot is cut into part
Figure : End milling

26. Profile Milling 26
A form of end
milling in which
the outside
periphery of a flat
part is cut
Figure : profile milling

27. Pocket Milling 27
Another form
of end milling
used to mill
shallow
pockets into
flat parts
Figure : pocket milling

28. Surface Contouring 28
Ball-nose cutter is
fed back and forth
across the work
along a curvilinear
path at close
intervals to create a
three dimensional
surface form
Figure : surface contouring

29. Milling Parameters
Illustrated
29
Figure :- Two forms of milling: (a) peripheral milling, and (b) face milling

30. Machining Calculations:
Milling
 Spindle Speed - N (rpm)
 v = cutting speed
 D = cutter diameter
 Feed Rate - fr (mm/min -or- in/min)
 f = feed per tooth
 nt = number of teeth
 Machining Time - Tm (min)
 Slab Milling:
 L = length of cut
 d = depth of cut
 Face Milling:
 w = width of cut
 2nd form is multi-pass
 Mat’l Removal Rate - MRR (mm3/min -or- in3/min)
30
r
m
f
DL
T


Dπ
v
N 
fnNf tr 
 
r
m
f
dDdL
T
-

 
r
m
f
wDw2L
T
-
-or-
r
w d fMRR 