Machine Design Databook Episode 2 part 4 pdf

18-3GThe loading efficiency of a differential screw, not including the collar friction Compound screws The loading efficiency of a compound screw, not including collar friction The number of

The total frictional torque for V-thread, including

collar friction torque

The mean diameter of collar

Substituting the value of dcin Eq (18-30a) and after

simplifying

The torque factor

The efficiency of square thread neglecting collar

friction

The efficiency formula for an angular-type thread

with half apex angle  and an allowance for nut or

end friction on a radius rc

The efficiency formula for square thread

LOADING

Lowering the load

The tangential force at mean or pitch radius r2 ¼ rm

The frictional torque at mean or pitch radius r2 ¼ rm

The condition for overhauling for square threads

Mt¼ W d2

2

tan  þ  cos 

1
 tan  cos 

0 B

1 C

A þ c dc2

2 6

tan  þ  cos 

1
 tan  cos 

0 B

1 C

A þ c  0:625 ð18-30dÞ

where d2 ¼ dm Refer to Table 18-5b for K

 ¼ tan  tan ð þ Þ ¼

Differential screws (Fig 18-3G)

The loading efficiency of a differential screw, not

including the collar friction

Compound screws

The loading efficiency of a compound screw, not

including collar friction

The number of threads necessary in the nut

The length of nut

Metric mechanical-property classes for steel bolts, screws, and studsa

TABLE 18-5d

Grade identification marks and mechanical properties of bolts and screws

ASTM A449

The required length of engagement for adequate shear

strength (assuming that the load is distributed over

the threads in contact)

Neglecting the radial clearance between threads, or

allowance at the major and minor diameters and

con-sidering the threads as a series of collars the equation

for thread engagement

The normal length of thread engagement as per

Indian standard

Note:

If leN has to be between the limits, the length of the

thread is said to be normal ðNÞ

If leN has to be below the minimum level, length of

thread is said to be short ðSÞ

If leN has to be above the maximum level, length of

thread is said to be long ðLÞ

Eccentric loading

The load on bolt 1, Fig 18-5 (panel a)

The general expression for the load carried by ith bolt,

Fi

The maximum load on the bolt, Fig 18-5(b)

The maximum load on the bolt, Fig 18-5(c)



180 8 i



Fastening of a bracket

Bracket with no preload

Tensile load taken by the bolts, Fig 18-6(a)

Shear stresses

(i) If shear load is taken completely by the lug, shear

load on lug is given by

(ii) If shear load is taken completely by the bolt shear

load on each bolt is given by

(iii) If shear load is shared equally between the bolt

and the lug

Shear load due to the eccentricity e, Fig 18-6(b), in

each bolt is given by

Resultant shear load

ð18-58Þ where xi¼ distance between the center of bolts and the center of the particular bolt

Fr ¼ Fbðor F0

bÞ þ P Fexi

x2 i

ð18-59Þ

FIGURE 18-5 Fastening of a flanged bearing

Preloaded bracket

Compression stress in contact area between the

bracket base and the wall, Fig 18-6(c)

Bending stress due to eccentric load, Fig 18-6(d)

Resultant compressive stress in the contact area

Tensile stress in any individual bolt is given by

Condition to avoid separation of the base and wall

With a 25% margin on the preload to account for

overloads, condition to avoid separation of the base

and wall

Bolt load taking into consideration 25% margin on

the preload to account for overloads

With an additional horizontal load Fh, the preload Fi

Shear load due to the eccentricity e in each of the bolts

with no horizontal load

Shear load due to eccentricity e in each of the bolts

with a horizontal load, Fh

Vertical applied load due to the friction component of

ð18-70Þ where

M1 ¼ Fe

 Mbc1 16Ic

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi

a2þ b2p

0 :25Mb

P

x0ic1A2bIcAc



ð88-70aÞ

where x0i¼ distance of the center of a particular bolt to the center of the base of the bracket

F
i ¼ M1xi P

x2 i

ð18-71Þ where

M1 ¼ Fe

"

 4



0 :25Mbc1

Ic Fh Ac

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi

a2þ b2

AbAc



0 :25Mbc1

Ic FhAc



ð18-73Þ

See Tables 18-6 to 18-22 and Figs 18-7 to 18-16 for

further particulars on threaded fasteners and screws

for power transmission.

For British Standard ISO metric precision hexagon

bolts, screws and nuts, and machine screws and

machine screw nuts.

For hexagon bolts, finished hexagon bolts, regular

square nuts, hexagon and hexagon jam nuts, finished

hexagon slotted nuts, regular hexagon and hexagon

jam nuts, carriage bolts, countersunk, buttonhead

and step bolts, machine screw heads, pan, truss and

100 8 flat heads, slotted head cap screws, square head

setscrews, slotted headless setscrews, etc.

For bolts, screws and nuts metric series—American

National Standards hexagon cap screws, formed hex

screws, heavy hex screws, recommended diameter–

length combinations for screws, hexagon bolts,

heavy hex bolts, heavy hex structural bolts, hexagon

nuts, slotted hex nuts, etc.

Refer to Tables 18-23 and 18-24.

Refer to Tables from 18-25 to 18-42.

All dimensions in inches.

Refer to Tables from 18-43 to 18-52.

Designation: A pitch diameter combination of thread size 8 mm and pitch 1 mm shall be designated as M8  1 M8 shall designate pitch diameter combina- tion of thread size 8 mm and pitch 1.25 mm.

FIGURE 18-7 Basic profile ISO metric screw threads

FIGURE 18-8 ISO metric screw thread design profiles of

external and internal threads

TABLE 18-7

Basic dimensions for design profiles of ISO metric screw threads

Minor diameter, mm Lead angle at basic

TABLE 18-7

Basic dimensions for design profiles of ISO metric screw threads (Cont.)

Minor diameter, mm Lead angle at basic

TABLE 18-7

Basic dimensions for design profiles of ISO metric screw threads (Cont.)

Minor diameter, mm Lead angle at basic

Source: IS: 4218-1967 (Part III)

FIGURE 18-9 Basic profile of square threads

TABLE 18-8

Basis dimensions (in mm) for square threads

TABLE 18-8

Basis dimensions (in mm) for square threads (Cont.)

Designation: A sawtooth thread of nominal diameter 48 mm and pitch 3 mm shall be designated as ST 48 3.

FIGURE 18-10 Basic profile of sawtooth threads (Source: IS 4696, 1968.)

TABLE 18-9

Basic dimensions (in mm) for sawtooth threads

TABLE 18-9

Basic dimensions (in mm) for sawtooth threads (Cont.)

Designation: A knuckle thread of nominal diameter 10 mm and pitch of 2.54 mm shall be designated as K10  2:54

FIGURE 18-11 Basic profile of knuckle threads (Source: IS 4695: 1968.)

TABLE 18-10

Basic dimensions (in mm) for knuckle threads

Pitch-diameter combinations for ISO metric threads

Pitch diameter of bolt threads 3 4 5 6 7 8 9

TABLE 18-16

Coarse-threaded series—UNC and NC (dimensions in inches)

Minor diameter internalthread classes 1B, 2B,

For complete manufacturing information and tolerances, see ASA Standard B1.1, 1949

TABLE 18-17

Fine-thread series UNF and NF (dimensions in inches)

Minor diameter internalthread classes 1B, 2B,

For complete manufacturing information and tolerances, see ASA Standard B1.1, 1949

TABLE 18-18

Extra-fine thread series—NEF

Minor diameter internalthread classes 1B, 2B,

For complete manufacturing information and tolerances, see ASA Standard B1.1, 1949

TABLE 18-19

8-pitch thread series—8N (dimensions in inches)

Sizeaalso Basic minor classes 1B, 2B, and 3B for Sizeaalso Basic minor classes 1B, 2B, and 3B for

Unified diameter-pitch relationships are marked UN

For complete manufacturing information and tolerances, see ASA Standard B1.1, 1949

FIGURE 18-13 608 unified and American Standard

screw-thread forms

FIGURE 18-14 American Standard screw thread

FIGURE 18-15 Whitworth screw thread

FIGURE 18-16 British Association screw thread

TABLE 18-20

12-pitch thread series—12N (dimensions in inches)

Sizeaalso Basic minor classes 1B, 2B, and 3B for Sizeaalso Basic minor classes 1B, 2B, and 3B for

aUnified diameter-pitch relationships are marked UN

For complete manufacturing information and tolerances, see ASA Standard B1.1, 1949

TABLE 18-21

16-pitch thread series—16N (dimensions in inches)

Sizeaalso Basic minor classes 1B, 2B, and 3B for Sizeaalso Basic minor classes 1B, 2B, and 3B for

Unified diameter-pitch relationships are marked UN

For complete manufacturing information and tolerances, see ASA Standard B1.1, 1949

TABLE 18-22

Proportions of power threads (dimensions in inches)

Size in Threads per inch Minor diameter Threads per inch Regular minor diameter Stub minor diameter

TABLE 18-23

British Standard ISO Metric Precision Hexagon Bolts, Screws and Nuts (BS 3692: 1967)

For general dimensions see Tables 2, 3, 4 and 5

Source: Courtesy British Standards Institution, 2 Park Street, London W1A 2BS, 1986

TABLE 18-24

British standard machine screws and machine screw nuts—metric series

For dimensions, see Tables 1 through 5

Source: Courtesy British Standards Institution, 2 Park Street, London W1A 2BS, 1986

TABLE 18-26

Regular unfinished square bolts21

Note: Bolt is not finished on any surface

Minimum thread length shall be twice the diameter plus1in for length up to and including 6 in and twice the diameter plus1in for lengths over 6 in.Thread shall be coarse thread series class 2A

TABLE 18-27

Finished hexagon bolts21

or basic major equal to

32 0.163 0.150 0.023 0.0095

TABLE 18-28

Regular square nuts21

TABLE 18-29

Hexagon and hexagon jam nuts21

Finished and regular Finished and regular

TABLE 18-30

Finished hexagon slotted nuts21

TABLE 18-32

Carriage bolts

TABLE 18-33

Countersunk, Buttonhead, and Step bolts

TABLE 18-34

Machine-screw heads (Cont.)

Note: Edges of head on flat- and oval-head machine screws may be rounded

Radius of fillet at base of flat- and oval-head machine screws shall not exceed twice the pitch of the screw thread

Radius of fillet at base of round- and fillister-head machine screws shall not exceed one-half the pitch of the screw thread

All four types of screws in this table may be furnished with cross-recessed heads

Fillister-head machine screws in sizes No 2 to3in, inclusive, may be furnished with a drilled hole through the head along a diameter at right angles

to the slot but not breaking through the slot