Me146 (Chapter 6)

Front 1

Used to hold the removable heads of cylinders, machine members that must be readily disassembled, and parts of large machines that must be built in small units for ease in manufacturing , assembling or shipping.

Back 1

Threaded bolts and screws

Front 2

Used for the transmission of power.

Sometimes used for adjusting or obtaining accurate movement in measuring instruments such as micrometers.

Back 2

Screws

Front 3

Type of thread that tends to weaken the screw, especially when it is subjected to shock and repeated stresses.

Back 3

V thread

Front 4

The tops and bottoms are flattened to increase strength and to make it easier to keep the threading tool sharp.

Back 4

American National thread

Front 5

Is the outside, or largest, diameter of the threads and is the nominal diameter.

Back 5

Major diameter

Front 6

Is the smallest diameter of the threads and is commonly called the root diameter.

Back 6

Minor diameter

Front 7

Is the mean of the major and minor diameters.

Back 7

Pitch diameter

Front 8

Is the area of an imaginary circle whose diameter is the mean of the pitch and minor diameters. The area is used for the purpose of computing the tensile strength.

Back 8

Stress area

Front 9

The thread that has the highest efficiency but is comparatively costly to make and adjustment for wear is difficult.

Back 9

Square thread

Front 10

Not so costly and adjustment for wear can be accomplished by using nuts split lengthwise, hence is used for power drives where there must be little or no backlash, such as feed screws and lead screws of machine tools. Efficiency isless than that of the square thread.

Back 10

Acme thread

Front 11

It is used when the power transmission is in one direction. The flat driving side retaining the efficiency of the square thread and the sloping side permitting adjustment bymeans of a split nut.

Back 11

Buttress thread

Front 12

Are used where both the head and nut can be made accessible by the use of flange connections and are the most satisfactory for of screw fastenings, since they can be easily renewed when broken or when the threads strips.

Back 12

Through bolts

Front 13

Have rough bodies and either rough or finished heads and nuts. Since it is not finished, the hole should be drilled 1/16 in. larger than the bolt.

Back 13

Machine bolts

Front 14

Are through bolts having finished bodies and are used with reamed holes. It is the proper construction when the bolt is subjected to shear loads.

Back 14

Coupling bolts

Front 15

Have no nuts, the screw passing through a clearance hole in one member and threadinginto the mating member. Are threaded for a length of 2 diameters plus ¼ in. and should enter the tapped hole at least one diameter in steel, 1.5 diameters for cast iron and 3 diameters for aluminum.

Back 15

Cap screws

Front 16

Are small screws, in the American Coarse and Fine Thread Series, designated by size numbers up to No. 12 (0.216 in.)

Back 16

Machine screws

Front 17

Obtainable in sizes up to 3/8 in. and are used with flat, round, oval fillister, binding and truss heads.

Back 17

Phillips cross-slot head machine screws

Front 18

Available on standard machine, wood and thread-forming screws. Available in sizes up to 3/8 in. and are used with flat, round, oval fillister, binding and truss heads.

Back 18

Clutch head

Front 19

Are threaded on both ends and are used where through bolts are undesirable.Preferable to cap screws since they need not to be removed when the joints are disassembled.

Back 19

Studs

Front 20

May be determined by measuring the stretch of the bolt during tightening.

Back 20

Bolt Tightening Load

Front 21

It is the arrangement wherein the threads are of the same "hand" and of different pitch the driven screw moves slowly.

Back 21

Differential screw

Front 22

It is the arrangement wherein the threads are of the opposite hand, driven screw moves rapidly.

Back 22

Compound screw

Front 23

Slow movement is obtained using a small helix angle and hence a small pitch, which gives a weak thread.

Back 23

Single screw

Front 24

If it is subjected to an axial load and to a turning moment, which induce in the screw direct tension or compression, torsional shear, shear across the root of the threads and compression between the thread surfaces, and if the axial load is compressive and the unsupported length is more than 6 or 8 times the thrust collar, it is treated as a column.

Back 24

Power screws