Design of Nut & Bolt A vehicle or a machine is an assembly of different parts arranged in definite order & is used to transform energy for doing some useful work. The connection between two parts can be either temporary or permanent. The temporary ts are 1. Screwed ts 2. Keys, cutter, & pin ts A screw thread is a form obtained by cutting a continuous helical groove on the cylindrical surface. The threaded portion engages with a corresponding threaded hole in the nut or machine part. Screws have two general purposes 1. To act as fastening to secure one member to other 2. To transmit power The first of the se purposes requires strong threads of low efficiency & they should not be loosened during the service. Screws used for transmission of power must have a high efficiency so as to reduce power loss during power transmission. Bolts: It is a cylindrical bar with an integral head at one end with threads at the other end. The cylindrical part of the bolt is known as shank. Forms of bolts:  Hexagonal- headed bolts various flanges in pressure vessels.  Square headed bolt: - This bolt is generally used when the head is to be accommodated in a recess. This recess also is made of square shape so that the bolt is prevented from turning when the nut is screved on or off it. This bolt is commonly used, Thickness of the bolt head – 0.8 D or D Width across fats-1.5 D+3mm When square headed bolt is to be used with its head projecting outside, it is provided with a neck of square cross section ,which fits into the corresponding square hole in the ading part.  Cylindrical or cheese headed bolt: - This bolt is used when the space for accommodating the bolt head is comparatively limited or where the use of spanner for holding is to be avoided . It is commonly used in big ends of connecting rods. The rotation of the bolt is prevented by means of a pin inserted the shank just below the head. The projecting part of this pin fits into the corresponding groove in the adjacent piese.  Cup headed or round headed bolt:- It is provided with the snug forged on the shank just below the head. It fits into the corresponding recess in the adjucent piece to prevent rotation of the bolt.  T. headed bolt:- It is used in machine tool tables in which T slots are cut to accommodate the Tea heads. The neck of this bolt also sometimes square in section.  Lifting Eye bolt:- It is used as an appliance for lifting heavy machines. It is screwed inside a threaded hole on the top of the machine.  Top bolt or cap screw:- It is a bolt used as a screw. i.e. screwed into a threaded hole instead of a nut.[sketch] It is used when it is not possible to accommodate the nut. It es loosely through a clear hole in a piece frequent insertion & removal of the top bolt is likely to damage the threads in the casting. Owing to this disadvantage,this method of fastening is employed only when parts are not to be

disconnected very often. Top bolts of various forns of heads similar to those of set screws are available. They are used for connecting the cylinder head with a cylinder of an internal combustion engine.  Shed bolt or stud :- It consist of only a cylindrical shank threaded at both ends. The length of only a cylindrical shank threaded at both ends. The length of plain portion depends upon the thickness Of the piece ading the nut. The stud is used in place of bolt when there is insufficient space to accommodate bolt head or to avoid use of an unnecessarily long bolt studs are commonly used to connect cylinder cover to engine cylinder. The lower end is screwed into the threaded hole in the casting by means of a stud driver, which consist of a thick hex gone nut having a partly threaded hole..  In this case it is not necessary to withdraw the stud when disconnecting the two pieces & hence the threaded hole does not get damaged. The disadvantage of tapbolt is overcome by using a stud. [sketch]  Set screws:- A set screw is similar to a tap bolt, but is threaded practically throughout its length. It is used to prevent relative movement. It is screwed into a tapped hole. In the piece ading the screw head, while its end presses on the other piece , thus preventing relative rotation or sliding. Following are the types of screws. 1. Round or cup [sketch] 2. Cylindrical or cheese [sketch] 3. Fillister [sketch] 4. Countersunk [sketch] 5. Rounded countersunk[instrument screw] [sketch] 6. Socket [sketch] 7. Grub screw [sketch] 8. Grub screw without heal [sketch] 9. Coller screw with a square head sketch]/ Ends of set screws, particularly grub screws are made in one of the following shapes Nuts :- Nuts are generally in the form of hexagonal or square prisms. Between Hex & square nuts, the hexagonal is generally given preference. The spanner used for turning the Nut can have better hold on a square nut than on hexagonal nut, but the angle through which the spanner will have to be turned to get another hold is only 60’ in case of a square nut.  1. 2. 3.  1. 2. 3. 4.

Hexagonal nut:Height T = D Width across Flat= 1.5D+ 3mm Angle of chamfer=R=1.8 D Square nut:Height or thickness=T=D W= 1.5D=3mm Angle of chamfer=30’ Radium of chamfer=R=2D [aprox]

Types of nuts for special purpose:1. Flanged nut:- This is a hexagonal nut provided with a cylindrical cap at the top

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to protect the end of the bolt from corrosion. It also prevent leakage through the threads. Cap nut:- It is also a hexagonal nut provided with a cylindrical cap at the top to protect the end of the bolt from corrosion. It also prevents leakage through the threads. Dome nut:- It is a form of a capnut having a spherical Domeat the top. Cylindrical or capstan nut:- This Nut is cylindrical in shape. Holes are drilled in the curved surface , for turning it with a tommy bar. Sometimes holes are drilled in the uppar face . For use of pin spannar for turning it. Ring nut:- It is in the form of a ring provided with slots in the curved surfaces for a special C spanner . These nuts are generally used in pairs . One nut acting as a lock nut for other Wing nut:- This nut can be easily operated by the thumb & a finger and is used where it is required to be adjusted frequently. It is used in a hacksaw. Washers:- A washer is cylindrical piece of metal placed below the nut to provide smooth bearing surface for the nut to turn on. It spreads the pressure of the nut from cutting into the metal & thus allows the nut to be screwwd on more tightly. Dia of washer=2D=3mm Thickness= 0.12D Angle of chart= 30’ Locking arrange merts for nuts:- Due to vibrations in the moving parts , There is always a tendancy for the nuts to get slack & to screw of the bolts slightly. The connected parts might get loose, & lead to serious breakdown. It is therefore desirable to secure the nut in some way so as to prevent it from getting loose. Lock nut or check nut:- This nut is used along with an ordinary nut. It is chamfered on both the hexagonal faces. Proper functioning of lock nut is in of case A but due to anavailability of small thickness spanner case B is adopted. Sometimes compromise is made by using two nuts of uniform thickness equal to 0.8 times the diameter of the bolt. As the top nut practically takes the whole load, thick nut should be there at the top. Nut with split pin:- Split pin is made from a steel wire of semicircular cross section, bent as shown. It is inserted in a hole drilled in the bsc 8’ that it bears on the top face of the nut, thus prevently it from turning. The split pin is also used in conjuction with special nuts designed for the purpose. Slotted nut:- It is a Hexagonal nut with slots cut in the upper end. A split pin is inserted through the slot which comes in line with. This nut is used in the ball t end in king pin of axle. Castle nut:- Slots are cut in a cylindrical collar provided on the top of the nut. These nuts are widely used in automobile & locomotive engine. Where they are subjected to sudden shocks & vibrations Sawn nut or wiles nut:- This is a hexagonal nut with a slot cut half way across it. A cap screw is ed through a clear hole in upper part & screwed into a tapped hole in lower part. On tightening the screw the friction between the

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thread in upper part & that in the bolt increases & prevents slackening of the bolt. Simmonds lock nut:- A collar is provided at the upper end of the hexagonal nut & a fibre ring is fitted inside it. The internal diameter of the ring is less than the core diameter of the bolt. The end of the bolt, on reaching the ring, cuts its own thread in the ring when the nut is screwed on. The thread gives a greetar grip over the bolt thread thus preventing the slackening. Spring washer:- A single coiled springor a double coiled spring placed under the nut as a washer , offers stiff resis tance when compressed by tightening of the nut & keeps the thread in the nut gripped eith the thread on the bolt. Nylock nut:- This nut is having a nylon rubber & when tigentened the nylon ring compresses & gives more grip Circlip [Retaining ring]:- This circlip is used to prevent the axial movement of parts inside it. This acts as a locking & retains the parts in assy.