Screws and Threads

14 questions

All types14 Multiple choice8 Numeric2 Ordering4

A jackscrew used for lifting heavy loads has a thread pitch of $\frac{1}{8}$ inch. How far will the load be lifted if the screw is turned exactly 4 complete revolutions?

\frac{1}{2}

inch

\frac{1}{8}

inch

4 inches

32 inches

Show answer & explanation

Answer: $\frac{1}{2}$ inch

Answer

The load will be lifted

\frac{1}{2}

inch.

The pitch of a screw indicates how far it will move linearly with one full revolution. To find the total distance the load is lifted, multiply the pitch by the number of complete revolutions. In this case, multiplying

\frac{1}{8}

inch by 4 revolutions equals

\frac{4}{8}

inch, which simplifies to

\frac{1}{2}

inch.

Step-by-Step Solution

Identify the distance the screw travels in one revolution.

The screw travels

\frac{1}{8}

inch per revolution.

The pitch of a screw defines its linear travel distance for exactly one

360

-degree turn.

Calculate the total distance for the given number of revolutions.

Multiply the pitch (

\frac{1}{8}

inch) by the number of revolutions (4).

The total linear distance is the product of the pitch and the total number of revolutions.

Solve the multiplication.

4 \times \frac{1}{8} = \frac{4}{8} = \frac{1}{2}

inch.

Simplifying the fraction gives the final total travel distance.

Key Concept

Screw Pitch and Linear Travel

Question 2Question →

A technician is comparing two threaded machine bolts of the same diameter. Bolt X has 10 threads per inch (TPI) and Bolt Y has 16 TPI. If both bolts are driven into a metal block using the exact same wrench, which of the following statements correctly describes how Bolt Y compares to Bolt X?

Bolt Y provides a greater mechanical advantage but advances a shorter linear distance per revolution.

Bolt X provides a greater mechanical advantage and advances a greater linear distance per revolution.

Bolt Y advances a greater linear distance per revolution because it has a higher thread count.

Both bolts provide the same mechanical advantage, but Bolt X advances faster.

Show answer & explanation

Answer: Bolt Y provides a greater mechanical advantage but advances a shorter linear distance per revolution.

Answer

Bolt Y provides a greater mechanical advantage but advances a shorter linear distance per revolution.

The correct answer accurately reflects the physics of a screw. A higher threads-per-inch (TPI) count (16 TPI for Bolt Y vs. 10 TPI for Bolt X) means the threads are closer together. This smaller pitch results in a shorter linear distance traveled per revolution. Because the effort force is applied over the same rotational distance (using the same wrench) but results in a smaller linear output distance, the mechanical advantage is greater. You trade distance for increased force multiplication.

Step-by-Step Solution

Determine the relationship between threads per inch (TPI) and pitch.

Pitch is the inverse of TPI. Bolt X has a pitch of 1/10 inch, while Bolt Y has a pitch of 1/16 inch.

Pitch defines the linear distance the bolt travels in one complete revolution.

Compare the linear advancement of both bolts.

Since 1/16 inch is less than 1/10 inch, Bolt Y advances a shorter distance per revolution than Bolt X.

A smaller pitch means less linear travel for each rotation.

Evaluate the mechanical advantage based on the pitch.

Bolt Y has a greater mechanical advantage than Bolt X.

A screw is essentially an inclined plane wrapped around a cylinder. A smaller pitch is equivalent to a shallower incline, which requires less effort force to move the load, thereby providing a higher mechanical advantage.

Key Concept

Screws and Threads

Estimated Time:1m 0s

Question 3Question →

A machinist tests two threaded shafts being driven into fixed, stationary bases. Shaft A is equipped with a $14\text{-inch}$ handle and standard right-hand threads at $4$ threads per inch (TPI). Shaft B is equipped with a $7\text{-inch}$ handle and left-hand threads at $8$ TPI. From a top-down view, the machinist turns the handle of both shafts exactly one full revolution clockwise. Assuming no friction, which of the following statements correctly describes the linear movement of the shafts and compares their Ideal Mechanical Advantage (IMA)?

Shaft A moves exactly

0.25

inches downward into the base, Shaft B moves exactly

0.125

inches upward out of the base, and both shafts possess the exact same IMA.

Both shafts move downward into their respective bases, but Shaft B possesses twice the IMA of Shaft A due to its finer thread pitch.

Shaft A moves exactly

0.25

inches upward out of the base, Shaft B moves exactly

0.125

inches downward into the base, and both shafts possess the exact same IMA.

Shaft A moves exactly

0.25

inches downward into the base, Shaft B moves exactly

0.125

inches upward out of the base, and Shaft A possesses four times the IMA of Shaft B.

Show answer & explanation

Answer: Shaft A moves exactly $0.25$ inches downward into the base, Shaft B moves exactly $0.125$ inches upward out of the base, and both shafts possess the exact same IMA.

Answer

Shaft A moves

0.25

inches downward, Shaft B moves

0.125

inches upward, and both shafts have the exact same Ideal Mechanical Advantage.

The correct answer accurately calculates that a clockwise turn drives a right-hand thread downward by its pitch (

1/4 = 0.25

inches) and a left-hand thread upward by its pitch (

1/8 = 0.125

inches). Furthermore, it recognizes that Ideal Mechanical Advantage (IMA) is the effort circumference (

2\pi R

) multiplied by the TPI. The larger

14\text{-inch}

handle on Shaft A exactly compensates for its coarser

4

TPI pitch, resulting in an identical IMA (

112\pi

) for both systems.

Step-by-Step Solution

Determine the direction of linear movement based on thread handedness.

Shaft A moves downward; Shaft B moves upward.

By convention, turning a standard right-hand thread clockwise drives it inward (downward into the base). Turning a left-hand thread clockwise drives it outward (upward out of the base).

Calculate the linear travel distance per revolution (pitch) for each shaft.

Shaft A travels

0.25

inches; Shaft B travels

0.125

inches.

Pitch is the reciprocal of Threads Per Inch (TPI). For Shaft A:

1 / 4 = 0.25

inches. For Shaft B:

1 / 8 = 0.125

inches.

Calculate the Ideal Mechanical Advantage (IMA) for Shaft A.

\text{IMA}_A = 112\pi

The IMA of a screw is the ratio of effort distance to load distance per revolution:

(2 \cdot \pi \cdot R) / \text{Pitch}

. For A:

(2 \cdot \pi \cdot 14) / 0.25 = 28\pi / 0.25 = 112\pi

Calculate the Ideal Mechanical Advantage (IMA) for Shaft B.

\text{IMA}_B = 112\pi

Applying the same formula for B:

(2 \cdot \pi \cdot 7) / 0.125 = 14\pi / 0.125 = 112\pi

. The doubling of the TPI exactly offsets the halving of the handle length, yielding identical IMA.

Key Concept

The IMA of a screw depends on both the length of the lever arm (handle) and the pitch of the threads, and thread handedness determines linear direction relative to rotation.

Question 4Question →

A jackscrew system has a stationary base containing a standard right-hand threaded nut. The screw, which has 4 threads per inch (TPI), supports a platform on its top. A technician uses a 1.25-foot long handle to turn the screw and lift a $720 \text{ lb}$ load exactly $2 \text{ inches}$ . Assuming $\pi \approx 3$ to simplify calculations and $100\%$ mechanical efficiency, which of the following correctly identifies the required rotation direction, effort force, and total work done?

Counterclockwise rotation; 2 lbs effort force; 1440 in-lbs total work

Clockwise rotation; 2 lbs effort force; 1440 in-lbs total work

Counterclockwise rotation; 24 lbs effort force; 1440 in-lbs total work

Counterclockwise rotation; 2 lbs effort force; 4 in-lbs total work

Show answer & explanation

Answer: Counterclockwise rotation; 2 lbs effort force; 1440 in-lbs total work

Answer

Counterclockwise rotation; 2 lbs effort force; 1440 in-lbs total work

Lifting the load requires backing the right-hand screw out of its nut, which means turning it counterclockwise. The IMA is calculated by matching units:

R = 15 \text{ inches}

and Pitch

= 0.25 \text{ inches}

. Using

\text{IMA} = \frac{2\pi R}{Pitch}

, the IMA is

\frac{90}{0.25} = 360

. The required effort force is the load divided by the IMA (

720 / 360 = 2 \text{ lbs}

). Finally, simple machines do not change total work; Work Out = Load

\times

Distance (

720 \text{ lbs} \times 2 \text{ inches} = 1440 \text{ in-lbs}

Step-by-Step Solution

Determine the required rotation direction for the screw.

Counterclockwise rotation.

A standard right-hand thread advances (moves inward/downward) when turned clockwise. To lift a load, the screw must back out of the base, which requires counterclockwise rotation.

Convert the handle length to inches and calculate the Ideal Mechanical Advantage (IMA).

R = 1.25 \text{ ft} = 15 \text{ inches}

. Pitch (

P

) =

\frac{1}{4} = 0.25 \text{ inches}

\text{IMA} = \frac{2\pi R}{P} = \frac{2(3)(15)}{0.25} = 360

Units must match (both in inches) to accurately calculate the mechanical advantage. IMA relates the circumference traveled by the effort to the linear pitch.

Calculate the required effort force.

\text{Effort Force} = \frac{\text{Load}}{\text{IMA}} = \frac{720 \text{ lbs}}{360} = 2 \text{ lbs}

The machine multiplies the effort force by a factor equal to the IMA (assuming

100\%

efficiency).

Calculate the total work done.

\text{Work} = \text{Load} \times \text{Vertical Distance} = 720 \text{ lbs} \times 2 \text{ inches} = 1440 \text{ in-lbs}

In any ideal machine, Work In equals Work Out. The total work performed against gravity depends only on the load weight and the distance it is lifted, regardless of the mechanical advantage.

Key Concept

Mechanics of Screws: Pitch, Mechanical Advantage, and Conservation of Work

Estimated Time:2m 0s

Question 5Question →

A mechanic has four different bolts. Arrange the bolts in order from the LEAST linear distance traveled per full revolution to the GREATEST linear distance traveled per full revolution.

Drag items to arrange them in the correct order

Show answer & explanation

Answer

The correct order from least to greatest linear travel is: 32 TPI, 20 TPI, 16 TPI, and 10 TPI.

The linear distance a screw travels in one full revolution is its pitch, which is calculated as 1 divided by the Threads Per Inch (TPI). A higher TPI means the threads are closer together, so the screw advances a shorter distance per turn. Therefore, to order them from least to greatest distance traveled, you must arrange them from highest TPI to lowest TPI: 32 TPI (1/32 inch), 20 TPI (1/20 inch), 16 TPI (1/16 inch), and 10 TPI (1/10 inch).

Step-by-Step Solution

Understand the relationship between threads per inch (TPI) and linear travel.

Linear travel per revolution, also known as pitch, is equal to 1 divided by the TPI.

Each full turn advances the screw by one thread pitch.

Determine the linear travel for each bolt.

32 TPI = 1/32 inch, 20 TPI = 1/20 inch, 16 TPI = 1/16 inch, and 10 TPI = 1/10 inch.

Applying the relationship pitch = 1 / TPI.

Order the calculated values from least to greatest.

1/32 < 1/20 < 1/16 < 1/10.

The question asks for the order starting with the least linear distance traveled.

Key Concept

The linear distance a screw travels in one revolution is its pitch. For standard screws, pitch is the reciprocal of the threads per inch (TPI). Therefore, a higher TPI results in a smaller linear travel per revolution.

Estimated Time:45s

Question 6Question →

A woodworker is selecting a replacement spindle for a workbench vise. They have four options with identical handle lengths and spindle diameters. Arrange the vise spindles in order from the one that applies the MAXIMUM clamping force for a given amount of effort, to the one that applies the MINIMUM clamping force.

Drag items to arrange them in the correct order

Show answer & explanation

Answer

The correct sequence is: 12 TPI, 8 TPI, 5 TPI, and 3 TPI.

The mechanical advantage of a screw determines how much clamping force is produced from a given effort force. It is inversely proportional to its pitch (the linear distance between adjacent threads). Threads per inch (TPI) is the inverse of pitch, meaning a higher TPI results in a smaller pitch. A smaller pitch creates a shallower thread angle, which maximizes the mechanical advantage and produces the greatest clamping force. Therefore, the spindle with 12 TPI applies the maximum force, while the one with 3 TPI applies the minimum force.

Step-by-Step Solution

Identify the relationship between Threads Per Inch (TPI) and pitch.

Pitch is the inverse of TPI. A higher TPI translates to a smaller pitch (distance between threads).

Understanding pitch is necessary to determine the mechanical advantage of the screw.

Relate pitch to mechanical advantage and clamping force.

A smaller pitch means the screw advances less linear distance per revolution, acting like a shallower inclined plane. This increases mechanical advantage, resulting in greater output clamping force for the same effort.

The question asks to order the spindles by the amount of clamping force applied.

Rank the spindles from maximum to minimum clamping force.

Maximum clamping force corresponds to the highest TPI. The correct order is 12 TPI, 8 TPI, 5 TPI, and 3 TPI.

This establishes the final required arrangement.

Key Concept

Mechanical Advantage of Screws Based on TPI

Question 7Question →

Rank the following jackscrew configurations in order from the highest Ideal Mechanical Advantage (IMA) to the lowest IMA.

Drag items to arrange them in the correct order

Show answer & explanation

Answer

The correct order from highest to lowest Ideal Mechanical Advantage is: the 8-inch handle with 8 TPI, followed by the 10-inch handle with 6 TPI, then the 12-inch handle with 4 TPI, and finally the 15-inch handle with 3 TPI.

The Ideal Mechanical Advantage of a jackscrew is determined by multiplying the circumference of the effort circle (

2 \times \pi \times L

) by the Threads Per Inch (TPI). Because

2\pi

is constant for all options, we can simply compare the product of the handle length (

L

) and the TPI. The 8-inch/8 TPI setup yields the highest proportional factor (

8 \times 8 = 64

), followed by the 10-inch/6 TPI setup (

60

), the 12-inch/4 TPI setup (

48

), and finally the 15-inch/3 TPI setup (

45

Step-by-Step Solution

Identify the formula for the Ideal Mechanical Advantage (IMA) of a jackscrew.

IMA = (2 × π × Handle Length) / Pitch. Since Pitch = 1 / TPI, this simplifies to IMA = 2 × π × Handle Length × TPI.

To find the relative IMA, we need to compare the product of the handle length and TPI for each configuration.

Calculate the proportional IMA factor (Handle Length × TPI) for each jackscrew configuration.

8-inch handle, 8 TPI: 8 × 8 = 64. 10-inch handle, 6 TPI: 10 × 6 = 60. 12-inch handle, 4 TPI: 12 × 4 = 48. 15-inch handle, 3 TPI: 15 × 3 = 45.

This provides a comparative numerical value to rank the mechanical advantages without needing to calculate the exact factor of 2π.

Order the configurations based on the calculated factors.

64 > 60 > 48 > 45.

The prompt requests ranking from the highest IMA to the lowest IMA.

Key Concept

Ideal Mechanical Advantage of a Screw

Question 8Question →

A technician is selecting a bench vise to clamp heavy metal parts securely. They want to use the vise that provides the greatest mechanical advantage, meaning it requires the least amount of effort force on the handle to generate a strong clamping force. If all available vises have the exact same handle length, which of the following thread designs should the technician choose?

A design with a smaller thread pitch (more threads per inch)

A design with a larger thread pitch (fewer threads per inch)

A design that uses left-handed threads instead of right-handed threads

A design with a thicker solid central threaded shaft

Show answer & explanation

Answer: A design with a smaller thread pitch (more threads per inch)

Answer

A design with a smaller thread pitch (more threads per inch)

A screw is essentially an inclined plane wrapped around a central cylinder. The thread pitch is the linear distance between adjacent threads. A smaller thread pitch represents a less steep inclined plane, meaning the vise jaw advances a shorter distance for each full revolution of the handle. Because the jaw moves less distance per turn, the effort force required to turn the handle is reduced, resulting in a higher ideal mechanical advantage and a stronger clamping force.

Step-by-Step Solution

Identify the relationship between a screw's threads and an inclined plane.

A screw is essentially an inclined plane wrapped around a cylinder.

Understanding the underlying simple machine explains how force is multiplied.

Determine how thread pitch affects the steepness of the inclined plane.

A smaller thread pitch (threads are closer together) creates a longer, less steep inclined plane over the same linear distance.

Pitch determines the linear distance the screw travels per revolution.

Relate the steepness to mechanical advantage and effort force.

A less steep inclined plane provides a higher mechanical advantage, meaning less effort force on the handle is required to generate the clamping force.

Mechanical advantage is the ratio of effort distance to load distance; a smaller pitch increases the effort distance per unit of clamping movement.

Key Concept

Mechanical Advantage of Screws

Estimated Time:45s

Question 9Question →

A facility operator needs to open a large industrial gate valve to allow water flow. The valve's stem features a standard right-hand thread with $5$ threads per inch (TPI). The valve is currently fully closed. To allow maximum water flow, the internal gate must be lifted exactly $3\text{ inches}$ . What action must the operator take to fully open the valve?

Turn the handwheel counterclockwise for

15\text{ full revolutions}

Turn the handwheel clockwise for

15\text{ full revolutions}

Turn the handwheel counterclockwise for

0.6\text{ of a revolution}

Turn the handwheel clockwise for

0.6\text{ of a revolution}

Show answer & explanation

Answer: Turn the handwheel counterclockwise for $15\text{ full revolutions}$ .

Answer

Turn the handwheel counterclockwise for

15\text{ full revolutions}

For a standard right-hand thread, counterclockwise rotation is required to withdraw or lift the mechanism. Since the stem has 5 threads per inch, it takes 5 full revolutions to move the gate 1 inch. To move the gate 3 inches, the operator must turn the handwheel

3 \times 5 = 15\text{ full revolutions}

Step-by-Step Solution

Determine the required direction of rotation.

Counterclockwise rotation.

Standard right-hand threads advance (close or move away) when turned clockwise. To lift the gate (open or move toward the operator), the handwheel must be turned counterclockwise.

Determine the linear distance traveled per revolution (pitch).

Pitch =

1 / 5\text{ inch}

per revolution.

TPI (threads per inch) tells us that

5\text{ threads}

fit in

1\text{ inch}

. The distance of a single thread (one revolution) is the inverse of the TPI.

Calculate the total revolutions needed to travel the target distance.

3\text{ inches} \times 5\text{ revolutions/inch} = 15\text{ revolutions}

Multiplying the total required distance by the number of threads per inch gives the total number of revolutions required.

Key Concept

Screw Pitch, TPI, and Thread Direction

Estimated Time:1m 0s

Question 10Question →

A lead screw on a lathe has 8 threads per inch (TPI). How far, in inches, will the carriage move if the screw is turned exactly 12 full revolutions?

Show answer & explanation

Answer: 1.5

Answer

1.5

Because the screw has 8 threads per inch, completing one full revolution advances the screw exactly 1/8 of an inch (0.125 inches). Turning the screw 12 times results in a total linear movement of 12 * 0.125 = 1.5 inches.

Step-by-Step Solution

Determine the pitch of the screw.

Pitch = 1 / 8 = 0.125 inches per revolution.

Pitch is the linear distance a screw travels in one complete revolution, which is the inverse of the TPI (Threads Per Inch).

Calculate the total linear distance traveled.

Distance = 0.125 inches/revolution * 12 revolutions = 1.5 inches.

Total distance is the product of the distance per revolution and the number of full revolutions.

Key Concept

The relationship between Threads Per Inch (TPI), pitch, and linear travel distance of a screw mechanism.

Alternative Method

Set up a proportion based on the definition of TPI: If 8 revolutions move the carriage 1 inch (since there are 8 threads in one inch), then 12 revolutions will move it 12 / 8 = 1.5 inches.

Estimated Time:45s

Question 11Question →

A mechanic is using a C-clamp with a threaded screw that has $16$ threads per inch (TPI). The clamp is currently open to a width of $5.0$ inches. If the mechanic needs to tightly secure two steel plates that have a combined thickness of $1.5$ inches, how many full revolutions of the screw are required to close the clamp to the exact thickness of the plates?

Show answer & explanation

Answer: 56

Answer

The screw must travel a linear distance of

3.5

inches to close the gap from

5.0

inches to

1.5

inches. With

16

threads per inch, each inch of linear travel requires

16

full revolutions. Multiplying the

3.5

inches of travel by

16

revolutions per inch yields exactly

56

revolutions.

Step-by-Step Solution

Calculate the linear distance the clamp's jaw needs to travel.

5.0 - 1.5 = 3.5

inches

The screw only needs to cover the empty space between the current opening and the target thickness of the plates.

Calculate the total number of revolutions based on the travel distance and TPI.

3.5 \times 16 = 56

revolutions

TPI (threads per inch) indicates that one full revolution moves the screw

1/16

of an inch. Therefore, moving it

1

inch requires

16

revolutions.

Key Concept

Linear Travel and Threads Per Inch (TPI)

Question 12Question →

A mechanic needs to lift a heavy engine using a screw jack. They can equip the jack with one of two interchangeable threaded rods: Rod X has a coarse thread with $4$ threads per inch (TPI), and Rod Y has a fine thread with $8$ TPI.

Assuming the jack's handle length is identical for both setups and friction is negligible, which of the following statements accurately describes the required effort force and total work done if the mechanic uses Rod Y instead of Rod X to lift the engine by exactly $10$ inches?

Rod Y requires half the effort force on the handle, but the total work done to lift the engine remains the same.

Rod Y requires half the effort force on the handle, and it reduces the total work done to lift the engine by half.

Rod Y requires twice the effort force on the handle, but the total work done to lift the engine remains the same.

Rod Y requires twice the effort force on the handle, and it doubles the total work done to lift the engine.

Show answer & explanation

Answer: Rod Y requires half the effort force on the handle, but the total work done to lift the engine remains the same.

Answer

Rod Y requires half the effort force on the handle, but the total work done to lift the engine remains the same.

A screw is essentially an inclined plane wrapped around a central cylinder. Increasing the Threads Per Inch from

4

8

halves the pitch of the thread, making the 'incline' less steep. This doubles the mechanical advantage of the jack, cutting the required effort force on the handle in half. However, the fundamental principle of all simple machines is that they do not reduce the total amount of work required to move a load; they merely trade increased input distance (more rotations of the handle) for decreased input force. Because the engine is still being lifted exactly

10

inches, the total output work remains identical.

Step-by-Step Solution

Analyze the relationship between Threads Per Inch (TPI) and pitch.

Rod Y (

8

TPI) has half the pitch of Rod X (

4

TPI), meaning it advances half the linear distance per full rotation.

Pitch is the mathematical inverse of TPI (

1/\text{TPI}

). It determines the steepness of the screw's thread.

Determine the effect of a smaller pitch on Mechanical Advantage and effort force.

Because Rod Y advances half as far per rotation, its Ideal Mechanical Advantage is doubled. Thus, it requires half the effort force to lift the same load.

A screw is an inclined plane wrapped around a cylinder. A finer thread equates to a shallower incline, which trades distance for force.

Evaluate the total work done by the system in both scenarios.

The total work done remains identical regardless of the rod used.

Total output work is calculated as Load Force

\times

Lift Distance. Since the engine's weight and the

10

-inch lift distance do not change, the total work is conserved.

Key Concept

Mechanical Advantage of Screws and Conservation of Work

Estimated Time:1m 0s

Question 13Question →

A technician is analyzing the thread specifications of four different fasteners to determine their linear travel. Assuming all fasteners have single-start threads, arrange them in order from the LEAST to the GREATEST linear distance they will travel into a fixed base for each full $360^\circ$ rotation.

Drag items to arrange them in the correct order

Show answer & explanation

Answer

The correct sequence from least to greatest linear travel per rotation is: the machine screw (20 TPI), the wood screw (1/16 inch pitch), the lag bolt (10 TPI), and finally the power screw (0.125 inch lead).

The sequence correctly calculates and compares the linear travel per rotation for each fastener. By converting all specifications to decimal inches (

0.05

in,

0.0625

in,

0.10

in, and

0.125

in), they can be accurately ordered from least to greatest.

Step-by-Step Solution

Define the relationship between threads per inch (TPI), pitch, lead, and linear travel.

For single-start threads, the linear travel per rotation equals the lead, which is equal to the pitch. Pitch can be calculated as

1 \div \text{TPI}

Establishing the mathematical formulas is necessary to compare different types of thread specifications on a single scale.

Calculate the decimal linear travel for the fasteners specified in TPI.

The machine screw travels

1 \div 20 = 0.05

inches per rotation. The lag bolt travels

1 \div 10 = 0.10

inches per rotation.

Converting TPI into decimal pitch allows for direct numerical comparison.

Convert the fractional pitch of the wood screw to a decimal.

The wood screw travels

1 \div 16 = 0.0625

inches per rotation. The power screw is already given as

0.125

inches.

Decimals provide a consistent format for sequential ordering.

Compare all decimal values and arrange them from least to greatest.

0.05

(machine screw)

< 0.0625

(wood screw)

< 0.10

(lag bolt)

< 0.125

(power screw).

Finalizes the sequence according to the explicit instructions in the stem.

Key Concept

The linear distance a screw travels in one full rotation is determined by its lead. For single-start threads, the lead equals the pitch, and the pitch is the reciprocal of the threads per inch (

P = 1 / \text{TPI}

Question 14Question →

A manufacturer is redesigning a manual screw press used for stamping metal. The press currently uses a single-start threaded spindle turned by a handwheel. To reduce the physical effort required by the operator to apply the necessary stamping force, which of the following design modifications should be made?

Increase the thread pitch of the spindle

Decrease the diameter of the handwheel

Increase the number of threads per inch (TPI) on the spindle

Replace the right-handed threaded spindle with a left-handed one of the same pitch

Show answer & explanation

Answer: Increase the number of threads per inch (TPI) on the spindle

Answer

Increase the number of threads per inch (TPI) on the spindle

A screw is essentially an inclined plane wrapped around a central cylinder. Increasing the number of threads per inch (TPI) decreases the pitch (the distance between adjacent threads). A smaller pitch acts like a shallower inclined plane, which increases the mechanical advantage of the system. With a higher mechanical advantage, the operator needs to apply less effort force to achieve the exact same clamping or stamping pressure.

Step-by-Step Solution

Identify the factors that determine the mechanical advantage of a screw mechanism.

Mechanical advantage depends on the ratio of the effort distance (handwheel circumference) to the load distance (thread pitch).

Understanding this relationship is required to determine how design changes affect the required input effort.

Evaluate the effect of increasing the threads per inch (TPI).

A higher TPI means the threads are closer together, resulting in a smaller thread pitch.

TPI and thread pitch have a direct inverse relationship.

Relate the smaller pitch to mechanical advantage.

A smaller pitch means the screw advances less per revolution, acting like a shallower inclined plane. This increases the overall mechanical advantage.

A higher mechanical advantage dictates that less input effort force is required to achieve the same output stamping force.

Key Concept

Mechanical Advantage of Screws

Estimated Time:45s

Screws and Threads

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