Wednesday, May 27, 2009

GDT - Geometric Dimensioning and Tolerancing

What Is GDT?
GDT is a symbolic language. It is used to specify the size, shape, form, orientation, and location of features on a part. And its defined by ASME Y14.5 standard. Features toleranced with GDT reflect the actual relationship between mating parts. Drawings with properly applied geometric tolerancing provide the best opportunity for uniform interpretation and cost-effective assembly. GDT was created to insure the proper assembly of mating parts, to improve quality, and to reduce cost. GDT is a design tool. Before designers can properly apply geometric tolerancing, they must carefully consider the fit and function of each feature of every part. GDT, in effect, serves as a checklist to remind the designers to consider all aspects of each feature. Properly applied geometric tolerancing insures that every part will assemble every time. Geometric tolerancing allows the designers to specify the maximum available tolerance and, consequently, design the most economical parts. GDT communicates design intent. This tolerancing scheme identifies all applicable datums, which are reference surfaces, and the features being controlled to these datums. A properly toleranced drawing is not only a picture that communicates the size and shape of the part, but it also tells a story that explains the tolerance relationships between features.

When GDT Is Used?

Many designers ask under what circumstances they should use GDT. Because GDT was designed to position size features, the simplest answer is, locate all size features with GDT controls. Designers should tolerance parts with GDT when Drawing delineation and interpretation need to be the same

1. Features are critical to function or interchangeability
2. It is important to stop scrapping perfectly good parts
3. It is important to reduce drawing changes
4. Automated equipment is used
5. Functional gaging is required
6. It is important to increase productivity
7. Companies want across-the-board savings

Welding symbols - explained for Drawing

The eight elements which may appear in a welding symbol are:- reference line, arrow, basic weld symbols, dimensions and other data, supplementary symbols, finish symbols, tail and specification and process or other reference. Let us discuss the one by one.
Reference Line: This is the basis of the welding symbol. All other elements are oriented with respect to this line. The arrow is affixed to one end and a tail, when necessary, is affixed to the other.
Arrow: This connects the reference line to one side of the joint in the case of groove, fillet, flange, and flash or upset welding symbols. This side of the joint is known as the arrow side of the joint. The opposite side is known as the other side of the joint. In the case of plug, slot, projection, and seam welding symbols, the arrow connects the reference line to the outer surface of one of the members of the joint at the center line of the weld. In this case the member to which the arrow points is the arrow side member: the other member is the other side member. In the case of bevel and J-groove weld symbols, a two-directional arrow pointing toward a member indicates that the member is to be chamfered.
Basic Weld Symbols: These designate the type of welding to be performed. The basic symbols which are shown in the table Basic Weld Symbols are placed approximately in the center of the reference line, either above or below it or on both sides of it as shown in above figure. Welds on the arrow side of the joint are shown by placing the weld symbols on the side of the reference line towards the reader (lower side). Welds on the other side of the joint are shown by placing the weld symbols on the side of the reference line away from the reader (upper side).

Supplementary Symbols: These convey additional information relative to the extent of the welding, where the welding is to be performed, and the contour of the weld bead. The “weld-all-around” and “field” symbols are placed at the end of the reference line at the base of the arrow as shown in first figure and the table Supplementary Weld Symbols.

Dimensions: These include the size, length, spacing, etc., of the weld or welds. The size of the weld is given to the left of the basic weld symbol and the length to the right. If the length is followed by a dash and another number, this number indicates the center-to-center spacing of intermittent welds. Other pertinent information such as groove angles, included angle of countersink for plug welds and the designation of the number of spot or projection welds are also located above or below the weld symbol. The number designating the number of spot or projection welds is always enclosed in parentheses.
Contour and Finish Symbols: The contour symbol is placed above or below the weld symbol. The finish symbol always appears above or below the contour symbol. The following finish symbols indicate the method, not the degrees of finish: C—chipping; G—grinding; M—machining; R—rolling; and H—hammering.
Tail: The tail which appears on the end of the reference line opposite to the arrow end is used when a specification, process, or other reference is made in the welding symbol. When no specification, process, or other reference is used with a welding symbol, the tail may be omitted.




i) To make the students understand and interpret drawings of machine components so as to prepare assembly drawings either manually and using standard CAD packages.
ii) To familiarize the students with Indian Standards on drawing practices and standard components.


Code of practice for Engineering Drawing, BIS specifications – Welding symbols, riveted joints, keys, fasteners – Reference to hand book for the selection of standard components like bolts, nuts, screws, keys etc.

Limits, Fits – Tolerancing of individual dimensions- Specification of Fits- Manual Preparation of production drawings and reading of part and assembly drawings.

Drawing, Editing, Dimensioning, Plotting Commands, Layering Concepts, Hatching, Detailing, Assembly, basic principles of GD&T (geometric dimensioning & tolerancing)

Manual parts drawing and preparation of assembled views given part details for components followed by practicing the same using CAD packages.
Suggested Assemblies:
Shaft couplings – Plummer block – Screw jack- Lathe Tailstock – Universal Joint – Machine Vice – Stuffing box- safety Valves - Non-return valves- Connecting rod -Piston and crank shaft- Multi plate clutch- Preparation of Bill of materials and tolerance data sheet

Friday, May 22, 2009

Kinematics of Machinery - ME 2203

In this unit you will be exposed to the topics like mechanism, links ,elements, kinematic pairs,degrees of freedom, inversion of mechanisms etc.

Pl follow the link given to download.

Readers are requested to go through the content provided ,and give their feed back using the post comment option below

Tuesday, May 12, 2009

Kinematics of Machinery ME1252

Kinematics is a branch of classical mechanics which describes the motion of objects without consideration of the causes leading to the motion. The other branch is dynamics, which studies the relationship between the motion of objects and its causes. Kinematics is not to be confused with kinetics, and to dynamics as used in modern day physics.
The simplest application of kinematics is for particle motion, translational or rotational. The next level of complexity is introduced by the introduction of rigid bodies, which are collections of particles having time invariant distances amongst themselves. Rigid bodies might undergo translation and rotation or a combination of both.
This is an initiative which I have meticulously consolidated to benefit my student and the learners of kinematics. Most of the content covers the syllabus III Semester Mechanical Engineering prescribed by Anna university .
Readers are also advised to update the vist and find the other links provided in this blog. They can also search using the keywords, by typing in the space provided in the top of this page.

1. Slider crank mechanism ppt :
2. Draw polygons -
3. Question bank :
4. Clutch assembly
5. Simple test on belts
6. Practice questions: Topic -belts
7. Formula for remembrance:
8. More formulae:
9.Introduction to belts
10.Kinematics question paper-sample

11. Kinematic mechanisms - Four bar chain, scotch yoke, slide crank and Geneva mechanisms

12. Fundamentals of gears

Kinematics of machinery - Gears

I have meticulously consolidated the content about gears. The link to download the content is given below. Have a look about the content and share your comments and views.Enjoy learning.....


Monday, May 11, 2009

Kinematic of machinery[ இயந்திர இயங்கியல்] - kom mechanisms

While browsing the internet I found these videos which are quite interesting and useful for learning the mechanisms.
The readers are requested to watch and comment about the collections and the content of this blog.

four bar chain

slider crank mechanism

scotch yoke mechanism

Geneva mechanism

Friday, May 8, 2009

Enthusiastic about the reader's response

I am happy that my blog is being viewed in around 28 countries in the globe of which few are listed.

Philippines,China,United States,Algeria,United Kingdom,Egypt,Nigeria,Venezuela,Pakistan,Turkey,Italy,Palestinian Territory,Sweden
Poland,Finland,Colombia,Europe,South Africa,Brazil,Korea, Republic Of Maldives,Taiwan

*Source STATCOUNTER as on 08.05.09

Keep updating your knowledge...
Happy blogging

Tuesday, May 5, 2009

Principles of Management MG1351

The following content is available in this blog, you can either search using the key word[ space provided in the top ],or click the link provided below. you can also expand the posts grouped in months.
POM MG1351

1. Question bank :
2. lesson from peter drucker
3. Subject content for POM
4. Case study :
5. Case study part 2
6. Case study part 1