DRILLING Drilling is a metal cutting process carried out by a rotating cutting tool to make circular holes in solid materials. Tool which makes hole is called as drill bit or twist drill.

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

A power operated machine tool which holds the drill in its spindle rotating at high speeds and when actuated move linearly against the work piece produces a hole.

Classification of Drilling Machines Based on construction: Portable, Sensitive, Radial, Up right, Gang, b)Based on Feed: Hand and Power driven

Sensitive Drilling Machine Drill holes from 1.5 to 15mm

Up-Right Drilling Machine Drill holes upto 50mm Table can move vertically and radially

Radial Drilling Machine It the largest and most versatile used fro drilling medium to large and heavy work pieces.

Gang Drilling Machine In this almost single purpose and more productive machine a number (2 to 6) of spindles with drills (of same or different size) in a row are made to produce number of holes progressively or simultaneously

Operations on Drilling Machine

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. Used to enlarge a hole

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. Special angled cone shaped enlargement at the end of the hole Cutting edges at the end of conical surface. Cone angles of 60°, 82°, 90°, 100°, 110°, 120

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 For cutting internal thread Multi cutting edge tool. Tapping is performed either by hand or by machine. Minor dia of the thread is drilled and then tapping is done.

Accurate Hole-making Pilot (Center) Drill Drilling Boring Reaming Sequence of Operations: Pilot (Center) Drill Drilling Boring Reaming

DRILL MATERIALS The two most common types are 1. HSS drill - Low cost 2. Carbide- tipped drills - high production and in CNC machines Other types are Solid Carbide drill, TiN coated drills, carbide coated masonry drills,

Tool Nomenclature

MILLING Machining operation in which work is fed 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

Figure 22.23 (b) vertical knee‑and‑column milling machine Vertical Mill Figure 22.23 (b) vertical knee‑and‑column milling machine

CNC Vertical Mill Column Head Table Saddle Knee Spindle Speed

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

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

Horizontal and Vertical Spindle Column and Knee type Milling Machines Fig : Schematic illustration of a horizontal-spindle column-and-knee type milling machine. Fig : Schematic illustration of a vertical-spindle column-and-knee type milling machine.

Arbors Fig : Mounting a milling cutter on an arbor for use on a horizontal milling machine.

Slab Milling The basic form of peripheral milling in which the cutter width extends beyond the workpiece on both sides

Slab Milling Slab milling also called as peripheral milling Cutters have straight or helical teeth resulting in orthogonal or oblique cutting action Fig : (a) Conventional milling and climb milling (b) Slab milling operation, showing depth of cut , d, feed per tooth, f, chip depth of cut, tc, and workpiece speed, v. (c) cutter travel distance lc to reach full depth of cut.

Slotting Width of cutter is less than workpiece width, creating a slot in the work

End Milling Cutter diameter is less than work width, so a slot is cut into part

Fig:Some of the basic type milling cutters and milling operations. Highly versatile machining operation Multitooth tool that produces a number of chips in one revolution Fig:Some of the basic type milling cutters and milling operations.

MILLING Addition to producing various external or internal round profiles,cutting operations can produce many other parts with more complex shapes Fig:Typical parts and shapes produced with the machining process

Milling parameters

Cutters for different types of Milling Fig : Cutters for (a) Straddle Milling, (b) form milling, (c) slotting, and (d) slitting with a milling cutter.

Other Milling Operations and Cutters Fig : (a) T-slot cutting with a milling cutter. (b) A shell mill.

Shaping Machine