Srinivasa Ram

GUIDE BLOCK 2

2011-05-15T01:59:00.000-07:00

GUIDE BLOCK

2011-05-15T01:58:00.000-07:00

A block attached in to the cross-head to work in contact with the guide bar.

CAVITY BLOCK

2011-05-15T01:57:00.000-07:00

A precast concrete block that contains a cavity or cavities.

BASE BLOCK

2011-05-15T01:56:00.000-07:00

A block of any material, generally with little or no ornament, forming the lowest member of a base, or itself fulfilling the functions of a base, as a member applied to the foot of a door or to window trim. A rectangular block at the base of a casing or column which the baseboard abuts.

STOP BLOCK 2

2011-05-15T01:55:00.000-07:00

STOP BLOCK

2011-05-15T01:54:00.000-07:00

The stop block is a device used primarily in woodworking (and in metalworking to a lesser extent as well) to ensure that the piece of wood or other material being worked upon is kept a certain, constant distance away from the cutting blade by allowing force to be applied to the material being cut in a direction perfectly parallel to the blade. This cutting device is typically a table saw, although stop blocks can be used with a variety of other machines, including radial arm saws and band saws.

Stop blocks generally run in a track cut into the saw's cutting surface, permitting it to move in only one direction (hence ensuring that all force is applied perfectly parallel to the cutting device, keeping the cut in a constant, straight line).

MODIFIED V BLOCK

2011-05-15T01:53:00.000-07:00

A block having a precise V -shaped groove for checking the roundness or concentricity of a machine part or the like, or for holding cylindrical pieces of work.

A square or rectangular steel block having a 90° V groove through the center, and sometimes provided with clamps to secure round work pieces.

Dimensional Details of COTTER AND SLEEVE JOINT

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COTTER JOINT WITH SLEEVE

2010-08-18T13:55:00.000-07:00

This type of cotter joint is used for connecting two rods which are subjected to axial forces. The ends of the two rods are enlarged in diameter to reduce the effect of reduction in the strength of the rods due to cutting of the slots. The enlarged ends of the rods are introduced from the opposite sides into a cylindrical sleeve to butt against each other at the mid length of the sleeve length. The slots in the rods and as well as in the sleeve are made slightly larger than. The slots in the two rods are so located with respect to the slots in the sleeve such that when assembled, there will be an offset by a small amount, called clearance, between them. This intentionally provided offset requires driving of the cotter into the slots by applying the force. As the cotter is driven, its straight side is forced against the straight faces of the slots in the sleeve, while its tapered side is forced against the tapered faces in the slots in the rods which results in the pulling of the two rods as to hold them rigidly by the friction grip. This assembly leaves clearance in the sleeve and the rods. The provision of these clearances facilitates the axial adjustments of the two connecting rods.

The dimensional details for Cotter Joint with Sleeve will be shown in the next post.

Cotter and Pin Joints

2010-08-17T08:02:00.000-07:00

Rods of circular and rectangular cross section subjected to axial tensile or compressive forces, are connected together by a cotter joint. It is a temporary method of fastening of the two rods which have to be frequently assembled and disassembled. Its chief advantages are that the joint can be quickly assembled and disassembled and rods occupy exactly the same relative positions after assembly. The cotter joints are used to connect the piston rod, to the same cross head of the steam engine, pump or compressor. Long tie bars in steel structures are some, times built up of round bar, of short lengths and jointed together by cotter joints.

SLOTTED NUT

2010-08-16T22:47:00.000-07:00

On the cylindrical surface of the nut, number of slots parallel to the axis is cut. The nut is operated by a C-Spanner. These are used in large screws for small pitches where adjustment by a spanner is convenient. The empirical proportions are based on the nominal diameter of the bolt.

WING NUT

2010-08-16T21:32:00.000-07:00

This type of nut is used where frequent turning on or off the nut is desired. This nut is operated by the thumb and a finger.

CAPSTUN NUT

2010-08-16T21:15:00.000-07:00

It is cylindrical in shape. Six holes are drilled in the curved surface of the nut for turning it with a Tommy bar introduced in these holes. Sometimes holes are also drilled in the upper flat face of the nut, for turning with a Tommy bar.

KNURLED NUT

2010-08-16T21:06:00.000-07:00

The nut is used when finger tightness and quick turning on or off is desired as in the case of terminals of electrical apparatus.

SQUARE- HEADED BOLT

2010-08-16T21:01:00.000-07:00

Square Head Bolts offer a large bearing area for positive gripping with an open or adjustable wrench. Length is measured from under the head.

DIFFERENCE BETWEEN A BOLT AND A SCREW

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A bolt is an externally threaded fastener designed for insertion through holes in assembled parts, and is normally intended to be tightened or released by torquing a nut. A screw is an externally threaded fastener capable of being inserted into holes in assembled parts, of mating with a preformed internal thread or forming its own thread, and of being tightened or released by torquing the head. An externally threaded fastener which is prevented from being turned during assembly and which can be tightened or released only by torquing a nut is a bolt. (Example: round head bolts, track bolts, plow bolts.) An externally threaded fastener that has thread form which prohibits assembly with a nut having a straight thread of multiple pitch length is a screw. (Example: wood screws, tapping screws.)

NUT

2010-08-16T20:59:00.000-07:00

A nut is a type of hardware fastener with a threaded hole. Nuts are almost always used opposite a mating bolt to fasten a stack of parts together. The two partners are kept together by a combination of their threads' friction, a slight stretch of the bolt, and compression of the parts. In applications where vibration or rotation may work a nut loose, various locking mechanisms may be employed: Adhesives, safety pins or lock wire, nylon inserts, or slightly oval-shaped threads. The most common shape is hexagonal, for similar reasons as the bolt head - 6 sides give a good granularity of angles for a tool to approach from (good in tight spots), but more (and smaller) corners would be vulnerable to being rounded off. Other specialized shapes exist for certain needs, such as wing nuts for finger adjustment and captive nuts for inaccessible areas.

SCREW

2010-08-16T20:58:00.000-07:00

A screw is a type of fastener characterized by a helical ridge, known as an external thread or just thread, wrapped around a cylinder. Some screw threads are designed to mate with a complementary thread, known as an internal thread, often in the form of a nut or an object that has the internal thread formed into it. Other screw threads are designed to cut a helical groove in a softer material as the screw is inserted. The most common uses of screws are to hold objects together and to position objects.

Often screws have a head, which is a specially formed section on one end of the screw that allows it to be turned, or driven. Common tools for driving screws include screwdrivers and wrenches. The head is usually larger than the body of the screw, which keeps the screw from being driven deeper than the length of the screw and to provide a bearing surface. There are exceptions; for instance, carriage bolts have a domed head that is not designed to be driven; set screws have a head smaller than the outer diameter of the screw; and J-bolts do not have a head and are not designed to be driven. The cylindrical portion of the screw from the underside of the head to the tip is known as the shank; it may be fully threaded or partially threaded.

The majority of screws are tightened by clockwise rotation, which is termed a right-hand thread. Screws with left-hand threads are used in exceptional cases. For example, when the screw will be subject to anticlockwise forces (which would work to undo a right-hand thread), a left-hand-threaded screw would be an appropriate choice.

Screw and Screw Threads

2010-08-16T20:57:00.000-07:00

A screw is a cylindrical or a conical rod with a helical groove cut on it. Its function is to transform the input motion of rotation into output motion of translation. A screw thread is a continuous helical ridge formed by cutting a helical groove on a cylindrical or conical shank. Basically screw threads are used to fasten the parts together, or to transmit motion and so power, or for the relative adjustments of the adjacent parts. To perform these specific functions, threads of different profiles are used. The shape of the different types of the standard thread profiles with proportions and their suitability for specific purpose are discussed here.

Design Analysis

2010-08-16T14:43:00.000-07:00

The designer assumes particular mechanisms, a particular material and mode of failure for the component with the whole of this information. This determines the dimensions of the product.

Design Synthesis

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It is a process of creating of selecting configurations, materials, shapes and dimensions for a product. It is a decision making process with the main objective of optimization. The objective can be minimum cost, minimum weight or volume, maximum reliability or maximum lift.

Steps involved in Machine Design

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1. Recognition of Need.

2. Design Synthesis.

3. Design Analysis.

4. Material Selection.

5. Design of Element.

6. Modification.

7. Detailed Drawing.

8. Production.

Factors to be considered in Machine Design

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1. Type of loads and stress caused by Load.

2. Motion of the parts or Kinematics of Machine.

3. Selection of Materials.

4. Form and Size of Parts.

5. Frictional Resistance and Lubrication.

6. Convenient and Economic features.

7. Use of Standard Parts.

8. Safety of Operation.

9. Workshop facilities.

10. Number of Machine to be manufactured.

11. Lost of Construction.

12. Assembly.

Design Based on methods used

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· Rational Design: This type of Designs depends upon Mathematics formula and Principle of Mechanics.
· Empirical Designs: This type of Designs empirical formula based on practice and past experience.
· Industrial Design: It depends upon production aspects to manufacture any machine component in the Industry.
· Optimum Design: It is the Best Design for the given object function under the specified constrains. It may be achieved by minimizing the undesirable effects.
· System Design: It is the Design of any complex machine system like a motor car.
· Element Design: It is the design of any element of the mechanical system like a piston, crank shaft, connecting rod etc.
· CAD: This type of design depends upon the use of computer system to assist in the creation. Modification. Analysis and optimization.

Machine Design

2010-08-15T22:47:00.000-07:00

It is the creation of new and better machines and improving the existing models. It is necessary to have a good knowledge of many subjects such as Mathematics, Engineering Mechanics, Solid Mechanics, Kinematics, Workshop Process and Engineering Drawing.

Ø In most cases the designer’s work is concerned with adaption of existing Design. This type of Design needs no special knowledge or Soft skills and can be attempted by Designers or Ordinary Technical Trainers. The Designers only make minor alteration or modification in the existing design of the product,

Ø Development Design:

This type of Designs need considerable scientific training and Design ability in order to modify the existing Designs into a new idea by adopting a new material or different method of Manufacture. In this case though the designer starts from the existing design, the final product may differ quiet markedly from the original product.

Ø New Design:

These types of designs need lot of Research, technical ability and creative thinking. Only those designers who have personal qualities of sufficiently high order can take up the work of new design.