User:Pratik93/sandbox


 * INTRODUCTION:-

Drilling is the operation of producing circular hole in the work-piece by using a rotating cutter called drill. A drilling machine comes in many shapes and sizes, from small hand-held power drills to bench mounted and finally floor-mounted models. They can perform operations other than drilling, such as countersinking, counter boring, reaming, and tapping large or small holes .Because the drilling machines can perform all of these operations, this chapter will also cover the types of drill bits, took, and shop formulas for setting up each operation. Safety plays a critical part in any operation involving power equipment. This chapter will cover procedures for servicing, maintaining, and setting up the work, proper methods of selecting tools, and work holding devices to get the job done safely without causing damage to the equipment, yourself, or someone nearby.


 * Characteristics & Uses:-

All drilling machines have the following construction Characteristics a spindle. sleeve or quill. column, head, worktable, and base. The spindle holds the drill or                                                                                             cutting tools and revolves in a fixed position in a sleeve. In most drilling machines, the spindle is vertical and the work is supported on a horizontal table. The sleeve or quill assembly does not revolve but may slide in its bearing in a direction parallel to its axis. When the sleeve carrying the spindle with a cutting tool is lowered, the cutting tool is fed into the work: and when it is moved upward, the cutting tool is withdrawn from the work. Feed pressure applied to the sleeve by hand or power causes the revolving drill to cut its way into the work a few thousandths of an inch per revolution. The column of most drill presses is circular and built rugged and solid. The column supports the head and the sleeve or quill assembly. The head of the drill press is composed of the sleeve, spindle, electric motor, and feed mechanism. The head is bolted to the column. The worktable is supported on an arm mounted to the column. The worktable can be adjusted vertically to the moving parts and lubricate the machines more often. Under extreme cold conditions, start the machines at a slow speed and allow the parts and lubricants to warm up before increasing the speeds. Metal becomes very brittle in extreme cold. so do not strike the machines with hard tools. Extreme heat may cause the motor to overheat. so use intermittent. or on and off, operations to keep the motor running cool.


 * USES:-

A drilling machine, called a drill press, is used to cut holes largest hole that can be drilled, the distance between the spindle and column, and the vertical distance between the worktable and spindle. into or through metal, wood, or other materials (Figure 4-1). Drilling machines use a drilling tool that has cutting edges at its point. This cutting tool is held in the drill press by a chuck or Morse taper and is rotated and fed into the work at variable speeds. Drilling machines may be used to perform other operations. They can perform countersinking, boring, counter boring, spot facing, reaming, and tapping (Figure 4-2). Drill press operators must know how to set up the work, set speed and feed, and provide for coolant to get an acceptable finished product. The size or capacity of the drilling machine is usually determined by the largest piece of stock that can be center-drilled (Figure 4-3). For instance, a 15-inch drilling machine can center-drill a 30-inch-diameter piece of stock. Other ways to determine the size of the drill press are by the accommodate different heights of work. or it may be swung completely out of the way. It may be tilted up to 90° in either direction, to allow for long pieces to be end or angled drilled. The base of the drilling machine supports the entire machine and when bolted to the floor, provides for vibration-free operation and best machining accuracy. The top of the base is similar to a worktable and maybe equipped with T-slots for mounting work too large for the table. A. Based on construction: a] Portable, Sensitive, Radial, up-right, Gang, Multi-spindle
 * Types of drilling machine:-

B. Based on Feed: B] Hand and Power driven

A. Bench mounting, B. Flour mounting,
 * Sensitive Drilling Machine:-

1] Drill holes from 1.5 to 15mm 2]Operator senses the cutting action so sensitive drilling machine •	3]It is designed for drilling small holes at high speed in light jobs. •	4]Drill holes from 1.5 to 15mm. •	5]It is designed to drill holes as small as 0.35mm in diameter. •	6] The machine is rotated at a high speed of 20,000 r.p.m. or above •	7] Operator senses the cutting action so sensitive drilling machine. •	8]High speed and hand feed are necessary for drilling small hole

9] High speeds are necessary to attain required cutting speed by            small diameter drill.

A. Round column section, B. Box column section
 * Up-Right Drilling Machine:-

* Drill holes up to 50mm * Table can move vertically and radically

It the largest and most versatile used fro drilling medium to large and heavy work pieces. (a) Plain radial drilling machine:
 * Radial Drilling Machine:-

In a plain radial drilling machine provisions are made for vertical adjustment of the arm, horizontal movement of the drill head along the arm, and circular movement of the arm in horizontal plane about the vertical column.

(b) Semi universal machine:- In a Semi universal machine, in addition to the above three movements, the drill head can be swung about a horizontal axis perpendicular to the arm.

(c) Universal machine:- In a universal machine, in addition to the above four movements, the arm holding the drill head may be rotated on a horizontal axis. The hand-feed drilling machines are the simplest and most common type of drilling machines in use today. These are light duty machines that are hand-fed by the operator, using a feed handle. so that the operator is able to “feel” the action of the cutting tool as it cuts through the workpiece. These drilling machines can be bench or floormounted. They are driven by an electric motor that turns a drive belt on a motor pulley that connects to the spindle pulley. Hand-feed machines are essentially high-speed machines and are used on small workplaces that require holes 1/2 inch or smaller. Normally, the head can be moved up and down on the column by loosening the locking bolts. wrenching it free of its holding device. Due to the high speed which allows the drilling machine to drill different heights of of these machines, operations that require drilling speeds less work. than 450 revolutions per minute cannot be performed. The power-feed drilling machines (Figure 4-6) are usually larger and heavier than the hand-feed. They are equipped with the ability to feed the cutting tool into the work automatically, at a preset depth of cut per revolution of the spindle, usually in thousandths of an inch per revolution. These machines are used in maintenance shops for medium duty work, or work that uses large drills that require power feeds. The power-feed capability is needed for drills or cutting took that are over 1/2 inch in diameter, because they require more force to cut than that which can be provided by using hand pressure. The speeds available on power-feed machines can vary from about 50 RPM to about 1,800 RPM. The slower speeds allow for special operations, such as counter boring, countersinking, and reaming. The sizes of these machines generally range from 17-inch to a 22-inch center-drilling capacity, and are usually floor mounted. They can handle drills up to 2 inches in diameter, which mount into tapered Morse sockets. Larger workplaces are usually clamped directly to the table or base using T-bolts and clamps, while small workplaces are held in a vise. A depth-stop mechanism is located on the head, near the spindle, to aid in drilling to a precise depth.
 * Hand-Feed:-
 * Power-Feed:-

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

Types of drills:
 * Drilling & Drill:-

1. Twist drill: Most common drill.

2. Step drill:Produces holes of two or more different diameter 3. Core drill: Used to make an existing hole bigger.

Special drills are needed for some applications that a normal high-speed industrial operations. Other types of special drills general purpose drill cannot accomplish quickly or accurately. are: left hand drill, Silver and Deming, spotting, slow spiral, Special drills can be twist drill type, straight fluted type, or fast spiral, half round, die, flat, and core drills. The general special fluted. Special drills can be known by the job that they purpose high-speed drill, which is the common twist drill used are designed for, such as aircraft length drills, which have an for most field and maintenance shops, can be reground and extended shank. Special drills are usually used in. adapted for most special drilling needs.
 * SPECIAL DRILLS*


 * Tool nomenclature:-

Operations that can be performed in a drilling machine are
 * Drilling operation:-

*Drilling *Reaming *Boring *Counter boring *Countersinking *Tapping

After the drill has been aligned and the hole started, then insert the proper size drill and continue drilling into the workpiece, while applying cutting fluid. The cutting fluid to use will depend on what material is being machined Use the cutting fluids freely.
 * DRILLING

Reaming Operations:- Reamer cutting edges should be sharp and smooth. For accurate sizes, check each reamer with a micrometer prior to use. Never start a reamer on an uneven or rough surface, and never rotate a reamer backwards. Continue to rotate the reamer clockwise, even while withdrawing from the hole. Use just enough feed pressure to keep the reamer feeding into the work. Excessive feed may cause the reamer to dig in and break or grab the work piece and wrench it from the vise.

BORING:- Occasionally a straight and smooth hole is needed which is too large or odd sized for drills or reamers. A boring tool can be inserted into the drilling machine and bore any size hole into which the tool holder will fit. A boring bar with a tool bit installed is used for boring on the larger drilling machines. To bore accurately, the setup must be rigid, machine must be sturdy, and power feed must be used. Boring is not recommended for hand-feed drilling machines. Hand feed is not smooth enough for boring and can be dangerous. The tool bit could catch the workpiece and throw it back at the operator. First, secure the work and drill a hole for the boring bar. Then, insert the boring bar without changing the setup. Use a dial indicator to set the size of bored hole desired by adjusting the tool bit in the boring tool holder; then, set the machine speed and feed. The speed is set at the speed recommended for drilling a hole of the same size. Feed should be light, such as 0.005 to 0.010 inch per revolution. Start the machine and take a light cut. Check the size of the hole and make necessary adjustments. Continue boring with a more rough cut, followed by a smoother finishing cut. When finished, check the hole with an internal measuring device before changing the setup in case any additional cuts are required. clean holes if used properly. Procedures for Countersinking:- Good countersinking procedures require that the countersink be run at a speed approximately one-half of the speed for the same size drill. Feed should be light, but not too light to cause chatter. A proper cutting fluid should be used to produce a smooth finish. Rough countersinking is caused by too much speed, dull tools, failure to securely hold the work, or inaccurate feed. The depth stop mechanism should be used when countersinking to ensure the recess will allow the flathead screw to be flush with the surface. Cutting Speed (v):- It’s the peripheral speed of the drill v = *D*N where D = dia 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
 * Definitions:-

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

Lubrication is important to remove heat and friction. Machines should be cleaned after use Chips should be removed using brush. T-slots, grooves, spindles sleeves, belts, pulley should be cleaned. Machines should be lightly oiled to prevent from rusting Special Care Operations under adverse conditions require special care. If Machines are operated under extremely dusty conditions. Operate at the slowest speeds to avoid rapid abrasive wear on the moving parts and lubricate the machines more often. Under extreme cold conditions, start the machines at a slow speed and allow the parts and lubricants to warm up before increasing the speeds. Metal becomes very brittle in extreme cold. so do not strike the machines with hard tools. Extreme heat may cause the motor to overheat. so use intermittent. or on and off, operations to keep the motor running cool. Lubrication:- Lubrication is important because of the heat and friction generated by the moving parts. Follow the manufacturer’s manual for proper lubrication methods. Clean each machine After use. Clean T-slots. grooves. and dirt from belts and pulleys. Remove chips to avoid damage to moving parts. Wipe all spindles and sleeves free of grit to avoid damaging the precision fit. Put a light coat of oil on all unpainted surfaces to prevent rust. Operate all machines with care to avoid overworking the electric motor.
 * Precautions for Drilling machine:-

Do not support the work piece by hand – use work holding device. Use brush to clean the chip No adjustments while the machine is operating Ensure for the cutting tools running straight before starting the operation. Never place tools on the drilling table Avoid loose clothing and protect the eyes. Ease the feed if drill breaks inside the work piece.
 * Safety Precautions:-