Chapter 7.DRILLING MACHINE

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OUTCOME 7:

OUTCOME 7 DRILLING MACHINE

Introduction:

Introduction In general, a drilling machine consists the following portion. BASE supports the weight of drilling machine WORK TABLE Holds the work piece rigidly in position while drilling. DRILLING HEAD Contains the mechanism used to revolve the cutting tool and advance into the work piece. The use of drilling machine is to produce HOLE in metal.

The structure of Drilling Machine:

The structure of Drilling Machine

Slide 4:

To drill a hole, two forces are required. A torque to provide the tangential cutting force . A direct thrust normal to the work piece to feed in the drill Thus, any drilling machine must provide these two motions to the drill.

Slide 5:

In order to produce accurate holes without damaging the drill, FOUR conditions must be fulfilled The drill must rotate without eccentricity (off center) The drill must cut equally on both cutting edges The feed motion must be along the line of the axis of the drill. The table must normally be at the right angle to the axis of rotation of the drill.

Slide 6:

These conditions are called the basic alignments of the machine and are illustrated in Figure 7.1. They are common to ALL drilling machines.

Figure 7-1 Main Alignments of A Drilling Machine:

Figure 7-1 Main Alignments of A Drilling Machine

Types of Drill:

Types of Drill Straight shank drill Driven by the friction forces between the shank and the chuck . May slip if the torque is greater than the friction grip.

:

Taper Shank Drill Made with a shallow taper of approximately 5/8 inch per foot diameter. Provide both friction drive and positive drive Friction Drive – the drill is pushed into a mating tapered hole and a considerable force is required to loosen it. Positive Drive – The end of the taper bears a tang , fits in a corresponding slot at the end of tapered hole in the spindle.

Taper Shank Drill vs. Straight Shank Drill:

Taper Shank Drill vs. Straight Shank Drill

Taper shank drill fits into Drilling Machine Spindle:

Taper shank drill fits into Drilling Machine Spindle

Taper Shank Drill:

Taper Shank Drill Advantages Positive drive – slip not likely to occur Good accuracy of concentricity Disadvantages Expensive

Drill Chuck:

Drill Chuck Used for holding straight-shank cutting tool. Common type – three jaw self centering . When the outer sleeve is turned, three jaws move simultaneously to hold the straight shank of cutting tool securely.

Drill Chuck:

Drill Chuck

Drill Chuck (Cont.):

Drill Chuck (Cont.) Two main types of Drill Chuck Key-tape Drill Chucks The sleeve is tightened with the key, causing the drill to be held securely and accurately. Keyless Drill Chucks The chuck may be loosened and tightened without a key.

Type of Drill Chuck:

Type of Drill Chuck KEYLESS DRILL CHUCK KEY TYPE DRILL CHUCK

Machine Spindle:

Machine Spindle The function Not only rotate but also provide a linear feed motion with necessary thrust for the feed. Transmit the rotary drive regardless of the movement of the spindle downwards and upwards.

Machine Spindle (Cont.):

Machine Spindle (Cont.) The structure Has ball thrust bearing at top and bottom. Any end play can be taken by adjusting a pair of lock nuts at the top Radial Bearing at both end of spindle sleeve to reduce the frictional force while rotating. Sleeve slides axially in the spindle housing. A gear mounted in the spindle housing engages with a rack cut in the back of the sleeve. A lever turns the gear thus moving the sleeves and the spindle upwards and downwards.

Machine spindle (Cont.):

Machine spindle (Cont.) The spindle drive pulleys or gears drive the spindle by a sliding key or spline . So , the spindle can move axially and still be driven in position. Steering Shaft Spline

Machine Spindle structure:

Machine Spindle structure

Question:

Question 1. Name two forces that have to be provided by drilling machines in order to produce holes in metal. Answer : A torque to provide the tangential cutting force. A direct thrust to feed the drill into the metal. 2. What are the advantages of taper shank drill over straight shank drill ? Answer : Slip not likely to occur. Good accuracy of concentricity. 3. What is the function of drill chuck ? Answer : Used to hold straight shank cutting tool.

Types of Drilling Machine:

Types of Drilling Machine Two Categories Fixed Axis Machine The work is moved into position under a fixed drill axis. Moving Axis machine The work is fixed and the drill axis moved into position over the hole.

Fixed Axis Machine:

Fixed Axis Machine The Sensitive Drilling Machine Small capacity, Maximum size of drill and do not have power feed. The term “sensitive” means the operator, by the hand feeding, can ‘feel’ the drilling cutting , particularly as it breaks through.

The Sensitive Drilling Machine:

The Sensitive Drilling Machine

The Sensitive Drilling Machine:

The Sensitive Drilling Machine Adjustment available Speed Adjustment by changing the belt on the pulley. Table height adjustment to accommodate different work height within spindle feed range. Table position adjustment enables the table to be swung clear to accommodate larger work-pieces. Spindle feed stop to allow holes to be drilled to a set depth.

The Pillar Drilling Machine:

The Pillar Drilling Machine More robust version of the sensitive drill. Floor mounted Provided with power feed usually at three rates. Wide range of spindle speeds provided by a gear box rather than by cone pulleys

The Pillar Drilling Machine:

The Pillar Drilling Machine

Pillar Drilling Machine:

Pillar Drilling Machine The speed range needs to be from 127 to 3714 rev/min and would usually be provided in nine steps The table can be swung clear of the base to allow large castings to be accommodated, as with sensitive drilling machine. Disadvantage – loses rigidity since the table cannot be support from underneath.

Pillar Drilling Machine (Cont.):

Pillar Drilling Machine (Cont.) A similar machine using box column is much more rigid as shown in Figure 7-5. However the table cannot be moved, to position the work under the drill.

Pillar Drilling Machine – Box Column Type:

Pillar Drilling Machine – Box Column Type

Compound-table Drilling Machine:

Compound-table Drilling Machine A table mounted on two sideways to give horizontal motions at 90 o to each other and controlled by lead-screws . The work is clamped to the compound table which can then be accurately adjusted to bring each hole centre under the spindle axis in turn for drilling.

Compound table:

Compound table

The use of compound table:

The use of compound table If the work is located accurately on the table, by locators in the tee slots , once the position of the first hole has been fixed, the remaining holes can be positioned by means of table movements without recourse the marking out. Ideal jobs for this type of machine are plates require large number of holes whose center coordinate specified as in Figure 7.7.

Figure 7-7 Typical Component For Drilling On A Compound Table:

Figure 7-7 Typical Component For Drilling On A Compound Table

Moving Axis Machines:

Moving Axis Machines Radial Drilling Machine The drilling head is mounted to move on slides along a radial arm which itself can be swung about the end column. The base of the machine itself is the worktable and is provided with tee-slots for clamping large work pieces. An auxiliary table is usually provided to which smaller work pieces can be clamped.

Radial Drilling Machine:

Radial Drilling Machine

Question:

Question 1. Name two categories of drilling machine. Answer : Fixed axis machine and moving axis machine. 2. What is the difference between fixed axis drilling machine and moving axis drilling machine ? Answer : Fixed Axis Machine Drilling axis is fixed and the work piece is movable Moving Axis Machine The work piece is fixed while the drilling axis is movable 3. Name three example of fixed axis drilling machine. Answer : Sensitive drilling machine, Pillar drilling machine, Compound table drilling machine.

Question (cont.):

Question (cont.) 4. What is the main features in sensitive drilling machine ? Answer : Hand feed (do not have power feed). Speed adjustment by pulley belts position. Table height adjustment. Table Position adjustment. The table is able to be swung clear. Spindle feed stop. 5. In what occasion, we should use compound table drilling machine ? Answer : When the work piece requires large numbers of holes.

Drilling Operation:

Drilling Operation There are several correct and safe procedure to be followed during the drilling operation. The machine table must be kept clean and in good condition. Dirt or burrs will destroy the machine correct alignment . Never drill into the table surface. Great care must be taken when producing thru holes. The holding of works by hands is dangerous. Work should always be held in the vice or clamped to the table.

How to Drill A Hole To A Set Depth:

How to Drill A Hole To A Set Depth If a blind hole is to be drilled, we cannot “guess” the depth of the hole. There are two ways to set the adjustable stop in order to get the hole with the required depth . Setting Total Depth of Hole By Gauge Blocks Setting Depth of full-diameter hole.

Setting Total Depth of Hole By Gauge Blocks:

Setting Total Depth of Hole By Gauge Blocks The stationary drill is brought down onto pile of a workshop grade gauge blocks of correct height. The feed stop is appropriately adjusted and locked.

Figure 7-10 (a): Setting Total Depth Of Hole By Gauge Blocks:

Figure 7-10 (a): Setting Total Depth Of Hole By Gauge Blocks

Setting Depth Of Full-diameter Hole:

Setting Depth Of Full-diameter Hole Drilling is started until full diameter is just obtained Machine is then stopped The stationary drill is brought down until it contacts the conical depression The feed stop is set so that the drill penetrates only to the depth required.

Setting Depth of Full-diameter Hole:

Setting Depth of Full-diameter Hole

How to Drill A Hole to A Set Depth (Cont.):

How to Drill A Hole to A Set Depth (Cont.) In both cases, the drill should be withdrawn as soon as the stop is reached. If it is allowed to rub , rapid overheating and wear will occur.

Correcting Hole Positions During Drilling:

Correcting Hole Positions During Drilling The technique of “boxing” hole when marking them out for drilling is recommended. However accurately the central punch mark is made, the drill may not position itself quite correctly. The off-centering can be detected by comparing the initial cone cut with the box.

Correcting Hole Positions During Drilling (Cont.):

Correcting Hole Positions During Drilling (Cont.) However, the comparison has to be made before the drill has attained its full diameter. The drill cannot be brought back to cut centrally once the drilled cone has reached full diameter

Figure 7-11 Correcting Hole Centre Position After Initial Error In Starting Drill:

Figure 7-11 Correcting Hole Centre Position After Initial Error In Starting Drill

Types of Drilling Operations:

Types of Drilling Operations There are several types of drilling operations can be done by using drilling machines Spot-Facing Counter-boring Tapping Reaming

Spot-Facing:

Spot-Facing When a bolt’s hole is drilled in a boss on a casting boss surface , the boss surface is rough and does not provide a good seating for bolt. Therefore, the boss surface has to be cleaned up or machined flat, by a spot facing cutter as shown in Figure 7-12(a).

Figure 7-12 Spot Facing With Blade-type Spot Facing Tool:

Figure 7-12 Spot Facing With Blade-type Spot Facing Tool

Spot Facing (Cont.):

Spot Facing (Cont.) The cutter is an interchangeable blade fitted in a cutter bar whose nose diameter is slightly less than that of drilled hole. The Nose act as the pilot for the cutter. The blade can also be fitted in the reverse position and used to spot-face an inside face.

Counter-boring:

Counter-boring The operation of enlarging the top of a previously drill hole to a given depth to provide a square shoulder for the head of a bolt or cap screw. The operation is performed with an end-cutting tool similar to a end mill but with a pilot to guide the tool and keep it concentric with the hole.

Counter-boring:

Counter-boring

Counter-boring & Spot-Facing Tool:

Counter-boring & Spot-Facing Tool

Tapping:

Tapping The operation of cutting internal threads in a hole with a cutting tool called a tap. Before we do tapping, a drill hole has to be produced. The size of the drill hole is equal to the minor diameter of the tap.

Tapping (Cont.):

Tapping (Cont.) The tapping of screw thread is usually a hand operation but machine alignments are used to ensure that the tap is correctly aligned with the hole. Tapping using drilling machine The tap is entered into the hole. The spindle is fed down until the centre engages with the center hole in the shank of the tap. The tap is turned by band in normal way to produce the thread.

Tapping:

Tapping Using Drilling Machine Free Hand by Tap Handle

Tapping Tool:

Tapping Tool

Reaming:

Reaming The operation of sizing and producing a smooth , round and precise hole from a previously drilled or bored hole with the use of a cutting tool called reamer . A very low speed must be used. A plentiful supply of cutting fluid is needed in order to wash away the swarf . Note : Swarf is shaving and chipping of metal

Reaming:

Reaming For the blind ream hole, the reaming should not be done to the full length of the drilled hole because clearance of chips is needed at the bottom of ream hole.

Reamer:

Reamer

Reamer:

Reamer

Question:

Question 1. If the thickness of work piece is 20 mm and the depth of blind hole that needs to be produce is 12 mm. What is the thickness of gauge blocks to set the drill ? Answer : 20-12=8 mm 2. Why we need to draw box around the hole marking before drilling ? Answer : So that any offset from the drilling can be easily identified before the drill attained its full diameter. 3. What is the common features of counter boring and spot facing tool ? Answer : Both of them have pilot nose whose diameter is slightly less than the drilled hole.

Question (Cont.):

Question (Cont.) Name the drilling operation needs to be carried out for the purposes below. a. Produces internal thread of the drilled hole Answer : Tapping b. Produces precision holes for dowel pins, bushes or shafts. Answer : Reaming c. Produces hole for screw head to sink inside especially cap head socket screw. Answer : Counter boring d. Produces flat surface for seating of nut or bolt head. Answer : Spot-facing