Drilling MCQ Quiz - Objective Question with Answer for Drilling - Download Free PDF

Explanation:

Drill Chuck in Drilling Machines

Definition: A drill chuck is an essential component of a drilling machine, designed to securely hold the drill bit in place during the drilling operation. It is a mechanical device that clamps onto the shank of the drill bit, ensuring it remains stable and aligned while the machine operates. The drill chuck is typically mounted on the spindle of the drilling machine and can accommodate various sizes of drill bits, making it a versatile tool in both industrial and home workshops.

Working Principle: The drill chuck operates by tightening around the shank of the drill bit using a key or a hand-tightening mechanism. When the drilling machine is activated, the spindle rotates, and the chuck transmits this rotary motion to the drill bit. This motion allows the drill bit to cut into the material being worked on, creating holes of various sizes and depths. The chuck's design ensures that the drill bit remains firmly in place, preventing slippage and ensuring precise and accurate drilling.

Types of Drill Chucks:

• Keyed Chucks: These chucks use a key to tighten and loosen the grip on the drill bit. The key engages with teeth on the chuck, allowing for a secure and tight grip on the drill bit.
• Keyless Chucks: These chucks do not require a key for operation. They can be tightened and loosened by hand, making them more convenient for quick bit changes. However, they may not provide as secure a grip as keyed chucks.
• Jacobs Chucks: A common type of keyed chuck, known for its reliability and durability. Jacobs chucks are widely used in various drilling machines and are available in different sizes to accommodate a range of drill bits.

Advantages:

• Versatility in holding different sizes and types of drill bits.
• Secure grip on the drill bit, preventing slippage during operation.
• Ease of use, especially with keyless chucks for quick bit changes.
• Durability and reliability, particularly with high-quality chucks like Jacobs chucks.

Disadvantages:

• Keyed chucks require a key, which can be inconvenient and may be misplaced.
• Keyless chucks may not provide as tight a grip as keyed chucks, leading to potential slippage in heavy-duty applications.
• Regular maintenance is required to keep the chuck in good working condition, such as cleaning and lubrication.

Applications: Drill chucks are used in a wide range of applications, including metalworking, woodworking, construction, and DIY projects. They are essential in tasks that require precise and accurate drilling, such as creating holes for fasteners, dowels, and electrical wiring. Drill chucks are also used in specialized drilling machines, such as bench drills, pillar drills, and CNC drilling machines, to accommodate different drilling needs.

Correct Option Analysis:

The correct option is:

Option 3: holds the drill bit.

This option correctly identifies the primary function of a drill chuck, which is to hold the drill bit securely in place during the drilling operation. The drill chuck ensures that the drill bit remains stable and aligned, allowing for precise and accurate drilling. Without a proper chuck, the drill bit would not be able to perform its task effectively, leading to poor quality holes and potential damage to the workpiece and the machine.

Additional Information

To further understand the analysis, let’s evaluate the other options:

Option 1: transmits rotary motion to the drill spindle at a number of speeds.

This option is incorrect because the drill chuck itself does not transmit rotary motion to the drill spindle. Instead, the spindle of the drilling machine transmits rotary motion to the chuck, which then transmits this motion to the drill bit. The spindle is responsible for the variable speeds and rotary motion, not the chuck.

Option 2: rests on the base and supports the head and the table.

This option is incorrect because the drill chuck does not rest on the base or support the head and the table of the drilling machine. These functions are typically performed by other components, such as the column, base, and table of the drilling machine. The chuck's primary role is to hold the drill bit, not to provide structural support.

Option 4: holds electric motor, V-pulleys, and V-belt.

This option is incorrect because the drill chuck does not hold the electric motor, V-pulleys, or V-belt. These components are part of the power transmission system of the drilling machine, responsible for driving the spindle and providing the necessary rotary motion. The chuck's role is to secure the drill bit, not to hold these power transmission components.

Conclusion:

Understanding the role and function of a drill chuck is essential for correctly identifying its importance in a drilling machine. The drill chuck is designed to hold the drill bit securely, ensuring precise and accurate drilling. While the chuck does not transmit rotary motion or provide structural support, its ability to clamp onto the drill bit is crucial for effective drilling operations. By evaluating the other options, it is clear that option 3 accurately describes the primary function of the drill chuck, making it the correct choice.

Rake Angle in Twist Drill:

• The rake angle in a twist drill is the angle formed between the leading edge of the drill bit and a perpendicular plane to the cutting surface. This angle is crucial for determining the cutting efficiency and the ease with which the drill bit penetrates the material.
• The rake angle in a twist drill is not constant; it changes along the cutting edge due to the drill's geometry.
• Near the dead center (chisel edge): The rake angle is minimum or even negative because the cutting velocity is low, and the material is pushed rather than sheared.
• Toward the periphery: The rake angle increases to a maximum as the cutting velocity becomes higher, improving cutting efficiency.

Explanation:

In this problem, we are tasked with determining the time taken to drill a 10 mm diameter hole through a 20 mm thick mild steel (M-S) plate using a drill bit running at 300 rpm with a feed rate of 0.25 mm/rev.

To find the time required for drilling, we need to understand the relationship between the feed rate, the thickness of the plate, and the rotational speed of the drill bit.

Step-by-Step Solution:

1. Understand the given parameters:

• Diameter of the hole (D) = 10 mm
• Thickness of the plate (T) = 20 mm
• Rotational speed (N) = 300 rpm
• Feed rate (f) = 0.25 mm/rev

2. Determine the total feed per minute:

The feed rate is given in mm per revolution (mm/rev), and the rotational speed is given in revolutions per minute (rpm). To find the total feed per minute, multiply the feed rate by the rotational speed.

Total feed per minute (F) = Feed rate (f) × Rotational speed (N)

F = 0.25 mm/rev × 300 rev/min = 75 mm/min

3. Calculate the total time required to drill through the plate:

The thickness of the plate is 20 mm. To find the time taken, divide the thickness of the plate by the total feed per minute.

Time (t) = Thickness of the plate (T) / Total feed per minute (F)

t = 20 mm / 75 mm/min ≈ 0.2667 min

Convert the time from minutes to seconds (since there are 60 seconds in a minute):

t = 0.2667 min × 60 sec/min = 16 seconds

Therefore, the time taken to drill the hole is 16 seconds.

Important Information:

When analyzing other options, we can see that:

• Option 1: 8 seconds - This would imply a feed rate or rotational speed that is significantly higher than what is given. Since the feed rate is already set at 0.25 mm/rev and the rotational speed is 300 rpm, an 8-second drilling time is not feasible with the given parameters.
• Option 3: 24 seconds - This would imply a feed rate or rotational speed that is significantly lower than what is given. With the provided feed rate and rotational speed, the drilling time would not extend to 24 seconds.
• Option 4: 32 seconds - Similar to option 3, this would suggest a much slower feed rate or rotational speed than what is provided. The calculated time based on the given parameters is 16 seconds, making 32 seconds an incorrect option.

Hence, based on the calculations and understanding of the feed rate, rotational speed, and thickness of the plate, the correct answer is indeed Option 2: 16 seconds.

Explanation:

Correct Option Analysis:

The correct answer to the statement "A bench mounted drilling machine is of the same type as a _____." is Option 1: sensitive drilling machine. Let's explore why this is the case.

Bench Mounted Drilling Machine:

A bench mounted drilling machine, also known as a bench drill, is a type of drill press that is mounted on a workbench or table. It is designed for precision drilling operations and is commonly used in workshops, laboratories, and small-scale manufacturing environments. The primary features of a bench mounted drilling machine include its compact size, ease of use, and ability to perform accurate drilling tasks on small to medium-sized workpieces.

Similarities to Sensitive Drilling Machine:

A sensitive drilling machine is a type of drilling machine that allows the operator to "feel" the cutting action of the drill bit as it penetrates the material. This sensitivity is achieved through a hand-fed mechanism that provides greater control over the drilling process. Sensitive drilling machines are typically used for drilling small holes in delicate or thin materials where precision is crucial.

The bench mounted drilling machine shares several characteristics with the sensitive drilling machine:

• Precision: Both machines are designed for high precision drilling operations. The bench mounted drilling machine's stable base and adjustable settings allow for accurate hole placement, similar to the control provided by a sensitive drilling machine.
• Size and Application: Both machines are suitable for small to medium-sized workpieces and are commonly used in workshops, laboratories, and small-scale manufacturing settings.
• Ease of Use: Both types of machines are user-friendly, making them suitable for operators who require precise control over the drilling process.
• Hand-Fed Mechanism: While not all bench mounted drilling machines have a hand-fed mechanism, many do, allowing the operator to manually control the feed rate and pressure, similar to a sensitive drilling machine.

Based on these similarities, it is clear that a bench mounted drilling machine is of the same type as a sensitive drilling machine, making Option 1 the correct answer.

Analysis of Other Options:

Let's analyze why the other options are not the correct answer:

• Option 2: Deep Hole Drilling Machine

A deep hole drilling machine is specifically designed for drilling deep holes with a high depth-to-diameter ratio. These machines are equipped with specialized tools and techniques to handle the challenges of deep hole drilling, such as ensuring straightness, managing heat, and evacuating chips. Deep hole drilling machines are used in applications such as the manufacturing of gun barrels, oil and gas drilling equipment, and aerospace components. They are significantly different in design and application compared to bench mounted drilling machines, which are not intended for deep hole drilling.

• Option 3: Radial Drilling Machine

A radial drilling machine is a large, versatile drilling machine characterized by its radial arm, which can be swung around to position the drill head over the workpiece without moving the workpiece itself. This machine is designed for drilling large workpieces and allows for easy adjustment of the drill head position. Radial drilling machines are commonly used in heavy industries for drilling large and heavy components. The design and functionality of a radial drilling machine are quite different from those of a bench mounted drilling machine, making this option incorrect.

• Option 4: Gang Drilling Machine

A gang drilling machine consists of multiple drill heads arranged in a line or a group, allowing multiple drilling operations to be performed simultaneously on a single workpiece. This type of machine is used for high-volume production where multiple holes need to be drilled in a specific pattern. Gang drilling machines are commonly used in automotive and manufacturing industries for repetitive drilling tasks. The setup and purpose of a gang drilling machine differ significantly from those of a bench mounted drilling machine, which is designed for single-hole precision drilling.

In conclusion, a bench mounted drilling machine shares the most characteristics with a sensitive drilling machine, making Option 1 the correct answer. The other options represent different types of drilling machines with distinct designs and applications, which are not directly comparable to a bench mounted drilling machine.

Explanation:

Drilling Operations and Coolants

Definition: In drilling operations, a coolant, also known as cutting fluid, is a fluid used to reduce the heat generated by the friction between the drill bit and the material being drilled. This ensures that the drill bit and workpiece remain at manageable temperatures, which is crucial for both the efficiency of the drilling process and the longevity of the equipment.

Working Principle: When a drill bit penetrates a material, it generates a significant amount of heat due to friction and the energy required to remove material. This heat can cause the drill bit to wear out quickly, distort, or even break if not properly managed. A coolant is applied to the drill bit and workpiece to absorb and dissipate this heat. The coolant flows over the drill bit and the cutting area, carrying away the heat and maintaining a stable temperature. This prevents overheating and allows for continuous, efficient drilling.

Advantages:

• Reduces the operating temperature of the drill bit, preventing overheating and extending its lifespan.
• Improves the quality of the drilled holes by maintaining optimal cutting conditions and reducing thermal expansion of the material.
• Decreases the amount of wear on the drill bit, reducing the frequency of tool replacement and maintenance.
• Enhances the overall efficiency of the drilling process by enabling higher cutting speeds and feed rates.

Disadvantages:

• Requires proper disposal and management as some coolants can be hazardous to the environment.
• Can add to the operational costs due to the need for coolant supply systems and regular maintenance.

Applications: Coolants are widely used in various drilling operations across different industries. They are essential in manufacturing processes, including automotive, aerospace, and construction, where precision and efficiency are crucial. Coolants are also used in smaller-scale operations such as DIY projects and hobbyist metalworking.

Analysis of Other Options:

Option 1: Clean the Drill Bit

While coolants do have some cleaning properties and can help in removing chips and debris from the drill bit and work area, their primary function is not to clean. Cleaning is more of an ancillary benefit rather than the main purpose. The main function of a coolant is to manage the temperature by cooling down the drill bit.

Option 3: Reduce Durability of Drill Bit

This option is incorrect as the purpose of a coolant is the exact opposite – to increase the durability of the drill bit. By cooling the drill bit and reducing wear, coolants help extend the life of the tool, ensuring it remains functional for a longer period.

Option 4: Heat the Drill Bit

This option is also incorrect. Heating the drill bit would be counterproductive as it would lead to faster wear and potential failure of the drill bit. The goal of using a coolant is to prevent the drill bit from overheating by cooling it down, thus maintaining its integrity and performance.

Explanation:

The helix angle is the angle between the leading edge of the land and the axis of the drill. Sometimes it is also called a spiral angle.

1. The helix results in a positive cutting rake. This angle is equivalent to the back rake angle of a single-point cutting tool.
2. The usual range of helix angle used in the drill is 20° to 35°.
3. Large helix angle 45° to 60° suitable for deep holes and softer work materials.
4. The small helix angle of less than 45° is suitable for harder and stronger materials.
5. Zero helix angles are used in spade drills for high production drilling, micro‐drilling, and hard work materials.

Important Points

1. An increase in helix angle is given for more quick removal of chips but a decrease in helix angle will give greater strength of cutting edges.
2. The larger the value of helix angle lesser will be the power required in drilling.

Explanation:

Centre Lathe → Knurling

Milling → Slotting

Grinding → Dressing

Drilling → Counter-boring

Knurling

Knurling is the operation of producing a straight-lined, diamond-shaped pattern or cross lined pattern on a cylindrical external surface by pressing a tool called knurling tool. Knurling is not a cutting operation but it is a forming operation.

A lathe is used for many operations such as turning, threading, facing, grooving, Knurling, Chamfering, centre drilling

Counter - boring

Counter - boring is an operation of enlarging a hole to a given depth, to house heads of socket heads or cap screws with the help of a counterbore tool.

Dressing:

When the sharpness of grinding wheel becomes dull because of glazing and loading, dulled grains and chips are removed (crushed or fallen) with a proper dressing tool to make sharp cutting edges.

The dressing is the operation of cleaning and restoring the sharpness of the wheel face that has become dull or has lost some of its cutting ability because of loading and glazing.

Slot Milling:

Slot milling is an operation of producing slots like T - slots, plain slots, dovetail slots etc.

Concept:

Drilling time can be calculated by;

\(T = \frac{L}{{f ~×~ N}}\)

where T = Machining time in min, L = (Approach Length + Thickness of plate) in mm, f = Feed (mm/rev), N = Speed in rpm (revolution per min)

\(Approach\ Length= \frac{D}{2\ tanθ}\)

Where θ = Half drill bit angle, D = diameter of the hole

∵ The angle of a drill bit is not given in the question hence we will take approach length zero.

∴ L = Thickness of the plate

Calculation:

Given:

Thickness of plate (L) = 30 mm, Feed (f) = 1 mm/rev, Speed (N) = 60 rpm, Hole diameter (d) = 25 mm

\(T = \frac{30}{{1 × 60}}\)

T = 0.5 min

T = 0.5 × 60 sec

T = 30 sec

Hence drilling time will be 30 sec.

Important Points

If in the ques it is given that "Neglect approach and over travel" OR "Drill bit angle is not given" then effective length equal thickness of the workpiece.

Explanation:

Drilling:

• Drilling is a cutting process in which a hole is originated by means of a multi-point, fluted, end cutting tool.
• As the drill is rotated and advanced into the work-piece, the material is removed in the form of chips that move along the fluted shank of the twist drill.
• The point angle is the angle between the cutting edges (lips).

• The point angle varies according to the hardness of the material to be drilled.

• The point angle is located at the head of the twist drill.
• For hard materials such as stainless steel, the point angle should be large and e.g. 130° or 135°.
• For soft materials, point angles of 60° are used i.e. for drilling wood and fibre.
• With a large point angle, more of the cutting edge engages in the workpiece when drilling.

Concept:

Advantages of radial drilling machine

• Drill head can be moved up and down.
• Drill head can be moved along the radial arm
• Radial drilling machines are used for heavy job which cannot moved around easily
• Radial drilling machines used for drilling number of holes in the job
• Radial drilling machine is powerful machine used for drilling large diameter hole.

Explanation :

Helix angle

• It is the angle formed by the leading edge of the land with a plane having the axis of the drill.
• Its usual value is 30°.
• The low-helix drill was developed primarily to drill brass and other thin materials like plastics. Because of its design, the low-helix drill can remove the larger volume of chips formed by high rates of penetration.
• High helix-drills are designed for drilling deep holes in aluminium, copper, die-cast material, and other metals where the chips have a tendency to jam in a hole. The angles vary between (35° - 45°).

Concept:

The depth of cut is the thickness that is removed as a workpiece is being machined.

The value of the depth of cut in the drilling operation is equal to half of the diameter of the drill.

\(Depth~of~cut=\frac{{Diameter~of~drill}}{{2}}\)

Calculation:

Given:

Depth of cut = 40 mm, Diameter of drill =?

\(Depth~of~cut=\frac{{Diameter~of~drill}}{{2}}\)

\(40 =\frac{D}{2}, D = 80~mm\)

Explanation:

Sensitive drill machine:

• This type of drilling machine is used to drill small holes at high speeds in lighter jobs or workpieces.
• The machine may be mounted on the bench or floor & the drilling work is started with the drill fed into the workpiece by purely hand control.
• Hand-feed permits the operator to sense the progress of the drill into the workpiece, so that if there is any drill worn out or jams it may be released immediately to prevent the drill bit from breaking.
• Since the operator senses the cutting action at any instant it is called the sensitive drilling machine.
• These machines are capable of drilling small holes of diameter as small as 0.35 mm to 15 mm. These machines run at a higher speed as high as 2000 rpm.

​Diagram of drilling tool:

here, we can see the shank is holding part of the drill which is held by the spindle.

​

Explanation:

Cutting Forces in Drilling:

The removal of material in conventional drilling is accomplished by the two main sharp cutting edges and small chisel edge connecting them. In a conventional twist drill, the following forces and their components act on the drill at its cutting edges.

1. A pair of tangential forces P_T1 and P_T2 are equivalent to cutting velocity (V) in turning.
2. A pair of axial force P_x1 and P_x2 on the main cutting edges.
3. A pair of radial force P_y1 and P_y2 acts in opposite directions and nullify each other.
4. One additional large feed (axial) force P_xe at the chisel edge.

The tangential component P_T1 and P_T2 produce the drilling torque T and result in power consumption P_c.

\(T =P_{T}\;\times\;\frac{D}{2}\)

P_c = 2πNT.

The total axial force: P_xT = P_x1 + P_x2 + P_xe.

In drilling, P_xT becomes very large mainly due to the force P_xe acting at the chisel edge. However, any radial or transverse force does not appear in drilling unless the drill loses its geometry.

Due to the large negative rake angle and negligible small cutting velocity, the chisel edge removes material more by extrusion or indentation rather than ideal machining i.e. shearing. The pair of tangential force P_T1 and P_T2 removes material ideally i.e. shearing.

∴ overall material removal in drilling is said to be done by shearing and extrusion both.

Concept:

Machining time for drilling:

\({T_m} = \frac{L}{{f \times N}}\)

D = diameter, N = speed in rpm of the drill, L = Length of axial travel in mm, f = feed