Question & Answer

The yield strength of a certain metal = 50,000 lb/in2 and its modulus of elasticity = 22 x 106 lb/in2. It

is to be used for the outer ring of a press-fit assembly with a mating shaft made of the same metal.

The nominal inside diameter of the ring is 1.000 in and its outside diameter = 2.500 in. Using a

safety factor = 2.0, determine the maximum interference that should be used with this assembly.

A steel collar is press fitted onto a steel shaft. The modulus of elasticity of steel is 30 x 10⁶ lb/in².

The collar has an internal diameter of 2.498 in and the shaft has an outside diameter = 2.500 in. The

outside diameter of the collar is 4.000 in. Determine the radial (interference) pressure on the

assembly, and (b) the maximum effective stress in the collar at its inside diameter

A gear made of aluminum (modulus of elasticity = 69,000 MPa) is press fitted onto an aluminum

shaft. The gear has a diameter of 55 mm at the base of its teeth. The nominal internal diameter of

the gear = 30 mm and the interference = 0.10 mm. Compute: (a) the radial pressure between the

shaft and the gear, and (b) the maximum effective stress in the gear at its inside diameter.

A pin made of alloy steel is press-fitted into a hole machined in the base of a large machine. The

hole has a diameter of 2.497 in. The pin has a diameter of 2.500 in. The base of the machine is 4 ft x

8 ft. The base and pin have a modulus of elasticity of 30 x 106 lb/in2, a yield strength of 85,000

lb/in², and a tensile strength of 120,000 lb/in2. Determine (a) the radial pressure between the pin and

the base and (b) the maximum effective stress in the interface

A dowel pin made of steel (elastic modulus = 209,000 MPa) is to be press fitted into a steel collar.

The pin has a nominal diameter of 16.0 mm, and the collar has an outside diameter of 27.0 mm. (a)

Compute the radial pressure and the maximum effective stress if the interference between the shaft

OD and the collar ID is 0.03 mm. (b) Determine the effect of increasing the outside diameter of the

collar to 39.0 mm on the radial pressure and the maximum effective stress.

A 1-8 UNC low carbon steel bolt (diameter = 1.0 in, 8 threads/in) is currently planned for a certain

application. It is to be preloaded to 75% of its proof strength, which is 33,000 lb/in² (Table 32.2).

However, this bolt is too large for the size of the components involved, and a higher strength but

smaller bolt would be preferable. Determine (a) the smallest nominal size of an alloy steel bolt

(proof strength = 120,000 lb/in2) that could be used to achieve the same preload from the following

standard UNC sizes used by the company: 1/4-20, 5/16-18, 3/8-16, 1/2-13, 5/8-11, or 3/4-10; and

(b) compare the torque required to obtain the preload for the original 1-in bolt and the alloy steel

bolt selected in part (a) if the torque coefficient in both cases = 0.20.

A 300-mm-long wrench is used to tighten a Metric 20x2.5 bolt. The proof strength of the bolt for

the particular alloy is 380 MPa. The torque coefficient is 0.21. Determine the maximum force that

can be applied to the end of the wrench so that the bolt does not permanently deform.

The designer has specified that a 3/8-16 UNC low-carbon bolt (3/8 in nominal diameter, 16

threads/in) in a certain application should be stressed to its proof stress of 33,000 lb/in² (see Table

32.2). Determine the maximum torque that should be used if C = 0.25.

A torque wrench is used on a 3/4-10 UNC bolt in an automobile final assembly plant. A torque of

70 ft-lb is generated by the wrench. If the torque coefficient = 0.17, determine the tensile stress in

the bolt.

Threaded metric fasteners are available in several systems, two of which are coarse and fine (Table

32.1). Finer threads are not cut as deep and as a result have a larger tensile stress area for the same

nominal diameter. (a) Determine the maximum preload that can be safely achieved for coarse pitch

and fine pitch threads for a 12 mm bolt. (b) Determine the percent increase in preload of fine

threads compared to course threads. Coarse pitch = 1.75 mm and fine pitch = 1.25 mm. Assume the

proof strength for both bolts is 600 MPa.

A 1/2-13 screw is to be preloaded to a tension force = 1000 lb. Torque coefficient = 0.22.

Determine the torque that should be used to tighten the bolt.

A Metric 16x2 bolt (16 mm diameter, 2 mm pitch) is subjected to a torque of 15 N-m during

tightening. If the torque coefficient is 0.24, determine the tensile stress on the bolt.

An alloy steel Metric 10x1.5 screw (10 mm diameter, pitch p = 1.5 mm) is to be turned into a

threaded hole and tightened to one/half of its proof strength. According to Table 32.2, the proof

strength = 830 MPa. Determine the maximum torque that should be used if the torque coefficient =

0.18.

A 3/8-24 UNF nut and bolt (3/8 in nominal diameter, 24 threads/in) are inserted through a hole in

two stacked steel plates. They are tightened so the plates are clamped together with a force of 1000

lb. The torque coefficient is 0.20. (a) What is the torque required to tighten them? (b) What is the

resulting stress in the bolt?

A 5-mm-diameter bolt is to be tightened to produce a preload = 250 N. If the torque coefficient =

0.23, determine the torque that should be applied.

There are 16 correct answers in the following multiple choice questions (some questions have multiple

answers that are correct). To attain a perfect score on the quiz, all correct answers must be given. Each

correct answer is worth 1 point. Each omitted answer or wrong answer reduces the score by 1 point, and

each additional answer beyond the correct number of answers reduces the score by 1 point. Percentage

on the quiz is based on the total number of correct answers.

32.1 Which of the following are reasons why mechanical assembly is often preferred over other forming

processes (two best answers): (a) ease of assembly, (b) ease of disassembly, (c) economies of scale,

(d) involves melting of the base parts, (e) no heat affected zone in the base parts, and (f)

specialization of labor?

32.2 Most externally threaded fasteners are produced by which one of the following processes: (a) cutting

the threads, (b) milling the threads, (c) tapping, (d) thread rolling, or (e) turning the threads?

32.3 Which of the following methods and tools are used for applying the required torque to achieve a

desired preload of a threaded fastener (three best answers): (a) arbor press, (b) preload method, (c)

sense of feel by a human operator, (d) snap fit, (e) stall-motor wrenches, (f) torque wrench, and (g)

use of lockwashers?

32.4 Which of the following are the common ways in which threaded fasteners fail during tightening (two

best answers): (a) excessive compressive stresses on the head of the fastener due to force applied by

the tightening tool, (b) excessive compressive stresses on the shank of the fastener, (c) excessive

shear stresses on the shank of the fastener, (d) excessive tensile stresses on the head of the fastener

due to force applied by the tightening tool, (e) excessive tensile stresses on the shank of the fastener,

and (f) stripping of the internal or external threads?

32.5 The difference between a shrink fit and an expansion fit is that in a shrink fit the internal part is

cooled to a sufficiently low temperature to reduce its size for assembly, whereas in an expansion fit,

the external part is heated sufficiently to increase its size for assembly: (a) true or (b) false?

32.6 Advantages of snap fit assembly include which of the following (three best answers): (a) components

can be designed with features to facilitate part mating, (b) ease of disassembly, (c) no heat affected

zone, (d) no special tools are required, (e) parts can be assembled quickly, and (f) stronger joint than

with most other assembly methods?

32.7 The difference between industrial stitching and stapling is that the U-shaped fasteners are formed

during the stitching process while in stapling the fasteners are preformed: (a) true or (b) false?

32.8 From the standpoint of assembly cost, it is more desirable to use many small threaded fasteners rather

than few large ones in order to distribute the stresses more uniformly: (a) true or (b) false?

32.9 Which of the following are considered good product design rules for automated assembly (two best

answers): (a) design the assembly with the fewest number of components possible, (b) design the

product using bolts and nuts to allow for disassembly, (c) design with many different fastener types to

maximize design flexibility, (d) design parts with asymmetric features to mate with other parts having

corresponding (but reverse) features, and (e) limit the required directions of access when adding

components to a base part?

Identify some of the general principles and guidelines that apply specifically to automated

assembly.

Identify some of the general principles and guidelines for design for assembly.

What are integral fasteners?

What is the difference between industrial stitching and stapling?

What are the advantages of snap fitting?

What is the difference between a shrink fit and expansion fit in assembly?

What is a rivet?

What are the three ways in which a threaded fastener can fail during tightening?

Define proof strength as the term applies in threaded fasteners.