LOCK NUTS and LOCKING DEVICES

Many different locking devices are used to prevent nuts from working loose. The following figure (p.525 Fig 37) illustrates various locking devices. A screw thread holds securely unless the parts are subject to impact and vibration (e.g. as in a car engine).

 

Various locking devices

 

A common device is the jam nut (A). Slotted nuts (L) and castle nuts (M), to be held with a cotter or wire, are commonly used in automotive industry.

Round nut locked by means of setscrew is shown at B. A brass plug is placed under the setscrew to prevent damage to the thread. This is a common type of adjusting nut used in machine-tool practice.

C is a locknut, in which the threads are deformed after cutting.

D, E and F are spring washers, also commonly used for locking.

In J a special tab is bent to secure the nut. At K, L and M, a particular pin known as a cotter pin is inserted through both nut and bolt, an then spread. (Refer to Appendix 28, p.700, for standard cotter pins)

Appendix 28 : Cotter Pins

 

WASHERS

Plain washers are commonly used in the assembly of nuts and bolts to provide a smooth surface for the nut or bolt to turn against.

Specifications are given by inside dia. , outside dia. , thickness , type.

For example, 1.375 x 2.500 x 165 type A suitable for use with 1 1/4 in. fastener (Refer App.27)

type "A" is a plain washer serie. Common sizes existed in two series; N (narrow) and W(wide)

 

Lock washers prevent a fastener from loosening due to vibration or stress.

In the above figure,spring washers D, E, F sometimes called tooth lock washers.

G, H are thicker and known as helical-spring lock washers.

Refer to Appendix 27, p.698, for plain and lock washers, for comparable nominal screw or bolt sizes.

Appendix 27A: Plain Washers

Appendix 27B: Lock Washers

 

KEYS

Key fasteners are used to prevent the rotation of wheels, gears etc. on their shafts.

 

Key nomenclature

Key is placed so that part of it lies in a groove cut on the shaft, called "key seat", and part of it fits into a groove cut in a hub, called "key way". Therefore, after the assembly locked together by the key, the shaft and hub will rotate together.

 

KEY TYPES

The simplest key is the square key, placed half in the shaft (H/2) and half in the hub (H/2). A flat key is rectangular in cross section, used similarly as square key. (Refer Appendix 25A, p.693)

Square (or Flat) key

The gib-head key is tapered on its upper surface and is driven in to form a very secure fastening. The head shape provides removal. (Refer Appendix 25B, p.693)

Gib-head key

The Pratt & Whitney key is rectangular in cross section and has rounded ends.It is placed two-thirds in the shaft (2/3*H) one-third in the hub (H/3). Key numbers are assigned to specify these keys.(Refer Appendix 25E, p.696)

Pratt&Whitney key

The most common key is the Woodruff key. This key is flat segmental disk with a flat (A) or round (B) bottom. Key numbers are assigned to specify these keys.(Refer Appendix 25C&D, p.694-695)

Woodruff keys, cutter and key seat

For very heavy duty, when keys are not sufficiently strong, splined shafts and hubs are used, arranged so that they fit one within other.

 

DIMENSIONING OF KEYS

For unit production nominal dimensions may be given (Fig. 45 p. 528)

For quantity production, the limits of width (and depth if necessary)

 

 

 

SPRINGS

 

A spring can be defined as an elastic body designed to store energy when deflected. Springs are classified according to their geometric form: helical or flat

 

HELICAL SPRINGS

Helical springs are further classified as: (1) Compression , (2) Extension , and (3) Torsion , according to the intended action.

On working drawings, helical springs are drawn as single-line convention.

 

For representation and dimensioning, the diameter (D) and pitch (P) of coils are laid. Refer Figures 50 - 51 - 52

 

Compression springs are wound with the coils separated so that the spring can be compressed, and the ends may be open or closed and may be left plain or ground. Refer Figure 50.

The information that must be given for a compression spring is as follows:

1- Controlling diameter: (a) is outside, (b) is inside, (c) operates inside a tube, or (d) operates over rod.

2- Wire or bar size

3- Material (kind and grade)

4- Coils: (a) total number and (b) right- or left-hand type

5- Style of ends

6- Load at deflected legth of ___

7- Load rate between ____ inches and ____ inches

8- Maximum solid height

9- Minimum compressed height in use

 

Extension springs are wound with the loops in contact so that the spring can be extended, and the ends are usually made as a loop. Special ends are sometimes required.

The information that must be given for an extension spring is as follows:

1- Free length: (a) overall, (b) over coil, or (c) inside of hooks.

2- Controlling diameter: (a) outside, (b) inside, or (c) inside a tube

3- Wire size

4- Material (kind and grade)

5- Coils: (a) total number and (b) right- or left-hand type

6- Style of ends

7- Load at inside hooks

8- Load rate, pounds per 1-in deflection

9- Maximum extended length

Torsion springs are wound with closed or open coils, and the load is applied torsionally (at right angles to the spring axis). The ends may be shaped as hooks or as straight torsion arms.

The information that must be given for a torsion spring is as follows:

1- Free length (dimension A, refer Fig. 52)

2- Controlling diameter: (a) outside, (b) inside, or (c) inside a hole, or (d) over a rod

3- Wire size

4- Material (kind and grade)

5- Coils: (a) total number and (b) right- or left-hand type

6- Torque, pounds at ___ deflection

7- Maximum deflection (degrees from free position)

8- Style of ends

 

FLAT SPRINGS

A Flat spring can be defined as any spring made of flat or strip material.

Flat springs are classified as:

- Simple flat springs, formed so that the desired force will be applied when the spring is deflected in a direction opposite to the force

- Belleville springs, stamped of thin material and shaped so as to store energy when deflected.

- Power springs, made as a straight piece and then coiled inside an enclosing case.

 

The information that must be given for a flat spring is as follows:

1- Detailed shape and dimensions of the spring shown in a drawing

2- Material and heat treatment

3- Finish

 

 

 

WELDING

Welding is a method for the permanent assembly of metal parts.

Arc welding can be divided at least three classes: arc welding, gas welding, and resistence welding.

1)Arc welding: Heat is generated by an electric arc and the parts are simply fused together
and became one. In some cases electrod is used that provides a filler material.

2) Gas welding: The burning gas (oxygen and acetylene) raises the temperature
of the part to be joined and a welding rod provides filler material.

3)Resistance welding: The parts that are to be welded, while being forced together
by mechanical pressure, are raised to the temperature of fusion by the passage of
a heavy electrical current through the junction.
(Filler materials are not used. One form is "spot welding")

There are five types and the types are named by the geometric relationship between the two parts.
BUTT, LAP, TEE, CORNER, EDGE

 

Before welding , the place of welding of the parts should be prepared.

There exist several types as shown in Figure 2. The type to be used is decided according to thickness of the parts to be welded.

For thicker parts grooves can be formed to have a complete penetration of weld. For thinner parts the edges can be bended.

 

Weld types, sizes and positions must be translated into symbols so that when a drawing is read, all the necessary information about a particular weld is clearly known.

Figure 4 gives the general welding symbol.

 

A welding drawing shows a unit or part made of several pieces of metal, with each welded joint described and specified. (e.g. Fig.15)

 

To indicate brazed joints conventional welding symbols may be used.

 

RIVETS

Rivets are used for making permanent fastening, generally between pieces of sheet or rolled metal.

They are round bars of steel with a head formed on one end and are often put in place red-hot so that a head can be formed on the other end by pressing or hammering.

 

 

There are two different joints: Lap and butt. As seen in figures: 19a - single riveted lap joint; 19b - double riveted lap joint, 19c - single strap butt joint and 19d - double strap butt joint

 

 

 

 

 

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