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DrD

Machine Design Methods

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Very right sir. I too have felt the same thing, although I might not be as experienced as you are. In fact, I have myself fallen into the trap. I, as a turbine designer, am not worried about the Navier stokes' and Reynolds' transportation theorems. What I know is that I have got an advanced CFD tool which can analyse any turbine operating point for me and I can then make necessary design optimizations. I don't know, if this way I shall ever become an expert in design or I shall become a mere CFD code operator!

As an older engineer, I am rather dismayed by what I see as the results of engineering education today. I have seen most young engineers come out of their college degree programs with a modest familiarity with come CAD program and a related Finite Element program, and an almost complete lack of capability to analyze machine components without the use of FEA. Thus they are unfamilliar with basic design calculations relating shear stress in a shaft to the power being transmitted, the shaft sped and the shaft diameter. Instead, they want to create an FEA model and run the numbers that way which is simply not the way you make any progress in designing a machine.

It is certainly true that FEA allows for a good detailed stress analysis of complex geometries, something that was not possible in general by the older methods. But the results obtained are highly dependent on the skill of the user in applying the correct boundary conditions, something that is a bit of an art in itself.

I have observed a tendency to even want to use FEA to do kinematics, rather than using simple, rigid body kinematic relations. This seems like pure foolishness in almost all cases. Are we not developing a tendency to lean too heavily on the computer, rather than to learn to think as engineers?

I would be happy to hear some comments and discussion from others on these matters.

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Yes saurabh is right,

I am doing my master's in CAD/CAM & Automation. Now, I am doing my project on FEA, but project dont include therotical design or analysis because my college guide dont want it. But now I am going to do therotical FEA.

Dr. D you are great.

Please continue to guide freshers like...

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The comment, "... or shall I become a mere CFD code operator" really hits the nail on the head. I am concerned that too many of our young engineers today are becoming simply code operators of one sort or another. I do not want to minimize the importance of the use of the computer at all; I have used it much over most of my career. But, it seems to me, the ccomputer always needs to be used to implement the understanding of the engineer, not to replace the understanding of the engineer which is the risk.

Many years ago, I had the opportunity to observe two new engineers from two competing schools, both hired at the same time by the company I was working for at the time. One had gone to a highly theoretical school that emphasized elaborate theoretical calculations. The other had gone to a much more design oriented school that emphasized practical, hand calculations - shear and moment diagrams, Mohr's circle, etc. Both of these young men were given design assignments soon after the were hired. The fellow from the practical school went straight to work and in a matter of a few weeks he had a completed dessgn with drawings, and the whole package. After several months, working on a comparable problem, the other engineer was still studying the problem trying to figure out where to start. You can guess which man succeeded in the company and which one was let go after about a year.

It is a balancing act. We are dependent on the computer for the detailed calculations that simply exceed human capability to perform, and yet we really need to be sure that we retain control of the situation, so that human intelligence guides the process, rather than simply calculations made by the machine.

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ABSOLUTELY RIGHT SIR.AS WE ARE YOUNG ENGINEERS HAVE MUCH DEPENDENCY ON MACHINE CALCULATIONS RATHER THAN OUR ENGINEERING SKILL ITS SHAME ON US,WHAT TO DO SIR IN COLLEGE EDUCATION IS BECOMING LEAN AND STUDENT DEDICATE HIS TIME TO SCORE ONLY MARKS, RATHER THAN UNDERSTANDING SUBJECTS WELL ,ALSO NOW A DAYS QUALITY OF EDUCATION IS BECOMING POOR,AND EVERY ONE DEPEND ON MACHINE FOR A SIMPLE CALCULATIONS.I ALSO EXPERIENCED SAME PROBLEM IN MY WORK ENVIRONMENT I'AM A DESIGN ENGINEER FOR SAKE OF NAME ONLY ALL WE DO IS ONLY DRAFTING ie CREATING A MODEL OR ASSEMBLY MODEL WITH THE HELP OF SOME 3D CAD TOOL & DRAFTING WILL M=BE MADE,THATS ALL SIR THEY DOESENT TEACH ANY DESIGN CONCEPT AT ALL ONLY DRAFTING.THIS IS NOT ONLY MY PROBLEM EVERY FRESH DESIGN ENGINEER WILL FACE SAME PROBLEM.

CAN YOU GIVE SOME SUGGESTION TO BECOME SKILL-FULL ENGINEER.HOPE YOU DO REPLY THANK U

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ABSOLUTELY RIGHT SIR.AS WE ARE YOUNG ENGINEERS HAVE MUCH DEPENDENCY ON MACHINE CALCULATIONS RATHER THAN OUR ENGINEERING SKILL ITS SHAME ON US,WHAT TO DO SIR IN COLLEGE EDUCATION IS BECOMING LEAN AND STUDENT DEDICATE HIS TIME TO SCORE ONLY MARKS, RATHER THAN UNDERSTANDING SUBJECTS WELL ,ALSO NOW A DAYS QUALITY OF EDUCATION IS BECOMING POOR,AND EVERY ONE DEPEND ON MACHINE FOR A SIMPLE CALCULATIONS.I ALSO EXPERIENCED SAME PROBLEM IN MY WORK ENVIRONMENT I'AM A DESIGN ENGINEER FOR SAKE OF NAME ONLY ALL WE DO IS ONLY DRAFTING ie CREATING A MODEL OR ASSEMBLY MODEL WITH THE HELP OF SOME 3D CAD TOOL & DRAFTING WILL M=BE MADE,THATS ALL SIR THEY DOESENT TEACH ANY DESIGN CONCEPT AT ALL ONLY DRAFTING.THIS IS NOT ONLY MY PROBLEM EVERY FRESH DESIGN ENGINEER WILL FACE SAME PROBLEM.

CAN YOU GIVE SOME SUGGESTION TO BECOME SKILL-FULL ENGINEER.HOPE YOU DO REPLY THANK U

I don't want to be harsh, but you are a big part of the problem. You are willing to work as a draftsman, therefore your employer is willing to pay you draftsman wages and have you do drafting work. If you want to be an engineer, you must insist that you will only do engineering work. I understand that this may mean that you have to look harder to find work, but that is the name of the game. If you find a better position, you should drop the previous employer like a hot rock. Engineers have low status because they accept it. The only way to get a higher status and better work is to demand it.

It appears to me that in many respects, the engineers of Asia, that is India and SE Asia, are doing relatively little to advance the profession these days. They are simply drawing on the "technical capital" that was developed by Western engineers over the past 300 years, the technology, the standards, etc., without doing a lot to develop new technology, etc. Your countries have taken away all of our manufacturing because your people are willing to work for such very low wages and with little or no environmental controls, and you are developing very little new. Why would you think that your employers would want real engineers? They are simply pirates who are stealing everything in sight, both from the West and from you and your people. For them, it is all about short term profits, and to blazes with tomorrow. You might do better yourselves to simply become highway robbers, bandits by the roadside. It is a popular thing these days in the corporate world, so why not take it to the outside world as well?

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Im 24, i work as a turbine designer, you can say im a young engineer, i calculate every bolt, every sheet, every welding, every shaft, flange etc, we use on our machines. but let me ask you a question sir? how in the hell are you going to do deadlines? the design process is quite complex due to all the variants that come into place at it stage of design, at first i did everything by hand, i by that i mean everything including FEA, the partial equations to solve a 10 or 20 element analysis were huge, and lets not talk about the time it took hours of work to do so! so i started to compare my results with the ones on our software, and the results were more accurate of course a machine can make solve 1000000000000000 faster the equations than us, i really disagree with what you are saying, i believe that at my young age i have a lot of experience on the field, although i would say that you need a great understanding of not only the software but the principle behind what you are analyzing before you start this task, if we are now using computer for designing its because its cheaper!! but of course it would be stupid to generate a 3d shape and doing an FEA to a shear stress analysis or a shaft calculation, but you need to do it in a F1 car drag analysis! its just matter of keeping things simple and useful, that is why we do what we do right?

I don't want to be harsh, but you are a big part of the problem. You are willing to work as a draftsman, therefore your employer is willing to pay you draftsman wages and have you do drafting work. If you want to be an engineer, you must insist that you will only do engineering work. I understand that this may mean that you have to look harder to find work, but that is the name of the game. If you find a better position, you should drop the previous employer like a hot rock. Engineers have low status because they accept it. The only way to get a higher status and better work is to demand it.

It appears to me that in many respects, the engineers of Asia, that is India and SE Asia, are doing relatively little to advance the profession these days. They are simply drawing on the "technical capital" that was developed by Western engineers over the past 300 years, the technology, the standards, etc., without doing a lot to develop new technology, etc. Your countries have taken away all of our manufacturing because your people are willing to work for such very low wages and with little or no environmental controls, and you are developing very little new. Why would you think that your employers would want real engineers? They are simply pirates who are stealing everything in sight, both from the West and from you and your people. For them, it is all about short term profits, and to blazes with tomorrow. You might do better yourselves to simply become highway robbers, bandits by the roadside. It is a popular thing these days in the corporate world, so why not take it to the outside world as well?

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As an older engineer, I am rather dismayed by what I see as the results of engineering education today. I have seen most young engineers come out of their college degree programs with a modest familiarity with come CAD program and a related Finite Element program, and an almost complete lack of capability to analyze machine components without the use of FEA. Thus they are unfamilliar with basic design calculations relating shear stress in a shaft to the power being transmitted, the shaft sped and the shaft diameter. Instead, they want to create an FEA model and run the numbers that way which is simply not the way you make any progress in designing a machine.

It is certainly true that FEA allows for a good detailed stress analysis of complex geometries, something that was not possible in general by the older methods. But the results obtained are highly dependent on the skill of the user in applying the correct boundary conditions, something that is a bit of an art in itself.

I have observed a tendency to even want to use FEA to do kinematics, rather than using simple, rigid body kinematic relations. This seems like pure foolishness in almost all cases. Are we not developing a tendency to lean too heavily on the computer, rather than to learn to think as engineers?

I would be happy to hear some comments and discussion from others on these matters.

i'm agree with you Professor, i'm young engineer...it's better to do first the old school and incorporate the latest technology..

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i'm agree with you Professor, i'm young engineer...it's better to do first the old school and incorporate the latest technology..

I SAW ALL THE COMMENTS, I AM SURPRISED THAT WITHOUT THEORETICAL KNOWLEDGE, HOW YOU CAN STIMULATE IN CFD OR ANY OTHER PROGRAM. THIS PROGRAMS ARE ONLY MATHEMATICAL TOOLS TO PERFORM THE CALCULATIONS AND TO SEE THE RESULTS. SUPPOSE IF YOU GET SOME PROBLEMS OR ANY OTHER ISSUE IS THERE THEN HOW YOU CAN SOLVE THAT?

WITHOUT PROPER KNOWLEDGE OF THEORY IT IS DANGEROUS TO USE THIS PROGRAM.

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respected sirs,

i m in 2nd year mechanical engineering , so what should i learn to be a better designing engineer ,..right now i have started learning AUTOCAD...please guide me....

hope i will get fruitful advises soon....

yes.. thats good, you must learn AutoCAD early,, after that, learn how to use AutoCAD Inventor for machine design and other mechanical engineering designs.. Good luck..

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I recorded a video training LIVE ONLINE to solve a similar problem...

What is the difference between the Job roles of a CAD Draughtsman and a Design Engineer ?

Are you confused between CAD Draugtsmen and Designer jobs ?

Which has better pay ?

Eliminate confusion now...

Discover these professional tips and you will easily increase your salary... I promise

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Hi Dr D,

I have encountered many engineers in my life time. Engineers today have proven that they can remember tons of formula and rules.

I think what you are saying is that; They have knowledge without understanding. I agree.

Engineering is not a religion. You shouldn't believe, you should understand.

If an engineer tells me he understands something, I listen. When he says he believes something I suspect he doesn't understand it.

Thanks for the topic,

John

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Respected sir,

 I am a 2nd year production engineering student,can u suggest me some books for getting good knowledge of designing.I'm actually wasting my time learning many software without knowing without knowing essence of designing.

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I have been thinking for a couple of days about your request for some good books on design. On the one hand, this is an easy question, but on the other hand it is very difficult.

First the easy answer. The machine design textbooks by Shigley (and usually a co-author) are very good, practical books. The same can be said of the books by Spotts. Both of these have put out a number of editions, and I could recommend any of them.

The hard part is that, you really cannot learn design from a book. You learn design by doing design. Design is about making all of the many decisions, both large and small, that going into completely specifying how something is to be made. Let me give you a simple example; consider a door hings. Everyone has seen a door hinge, so the working concept should not require any explanation.

But now, the boss has told you to design a door hinge. How big should the hinge be? He did not say, but you know it has to be big enough to do the job, but not so big as to waste a lot of material. How big is that? I don't know, but you as the designer must decide.

How many screw holes should there be in each leaf? The boss did not say, but you as the designer must decide how many, and where, the screw holes go.

What material is the hinge to be made from? The boss did not say, but you as the designer must decide. This will be based on the application and on the machines and tools available in your shop to make the hinge.

How thick should the leaves be? The boss did not say, but you as the designer must decide and specify the material thickness.

What is the heat treatment to be? You have to decide.

Is the hinge pin to be hardened, and if so, to what hardness? You have to decide.

This is only the beginning, and this is a super simple project. One of the things you will learn rather quickly is that it is a waste of time to try to optimize every aspect of the design. You may profitably spend some time trying to minimize manufacturing cost, or overall cost, but it is a waste to worry about maximizing fatigue life in this example. (In some other cases, maximizing fatigue life may be the most critical consideration.)

Design is about making decisions, and you learn that by making decisions and observing the results of your decisions.

DrD

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Dr. D, an excellent answer and one that will not be fully appreciated until someone has designed something. The books will provide a lot of information but until you have been forced to juggle all the variables and decide what is critical and what is not you can not appreciate what design is. The home garage mechanic may be very good at getting things built for himself but creating a product is another world. He often uses what is on hand so the material selection is by default. He is the only customer and likely what he builds is a one-of-a-kind with a specific application. The example of the hinge is a good one. Blacksmiths have been hammering out hinges long before there was an MIT. In the beginning it was one project at a time, (project vs. product is an article onto itself). It is hard to imagine a bad hinge. That is because we have not seen all the development that went into it over centuries. The Dyson vacuum is a good product. In one commercial Mr. Dyson mentions 5,000 prototypes to get to the final product. Say there were only 10 decisions per prototype that would be 50,000 for a vacuum. Now think about an automobile then the Saturn V Rocket. I assisted for a short time a young man who was building a device used in cross country skiing. At first glance you would take it for granted as we would a hinge. During our conversation I commented on how many detailed there were. He pulled a Big pen from his pocket and said he looks at an item as simple as a pen as sees all the decisions that must be made. You can't get that from a book.

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Thanks for the comment, Joe.

I would like to reinforce one part of Joe's comment:

The home garage mechanic uses what is on hand, so the material selection is by default. This is oh, so true. The home mechanic uses whatever is available to him. The design engineer must assume that the whole world, or at least most of it, is available to him, so he has no default position. He can order steel, brass, copper, tin, bronze, plastic, etc from countless suppliers, but there is nothing on the shelf for him to simply point to.

Speaking of the manufacture of a pen reminds me of a story. Some 30 years ago, I visited Parker Pen in Janesville, WI where they  were making ball point pins. This was a field trip organized by an ASME Senior Section. While we were there, they ran a special batch of pen for us with the ASME logo on them. It was pretty amazing to watch.

We think of a pen as a long cylinder, but they were starting with small disks cut from flat sheet steel. These where then drawn progressively over a mandrel to produce the tube that forms the barrel of the pen, a very deep draw! I was truly amazed to see this done, and they were cranking them out by the thousands.

DrD

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On ‎12‎/‎15‎/‎2008 at 3:19 PM, DrD said:

As an older engineer, I am rather dismayed by what I see as the results of engineering education today. I have seen most young engineers come out of their college degree programs with a modest familiarity with come CAD program and a related Finite Element program, and an almost complete lack of capability to analyze machine components without the use of FEA. Thus they are unfamilliar with basic design calculations relating shear stress in a shaft to the power being transmitted, the shaft sped and the shaft diameter. Instead, they want to create an FEA model and run the numbers that way which is simply not the way you make any progress in designing a machine.

 

It is certainly true that FEA allows for a good detailed stress analysis of complex geometries, something that was not possible in general by the older methods. But the results obtained are highly dependent on the skill of the user in applying the correct boundary conditions, something that is a bit of an art in itself.

 

I have observed a tendency to even want to use FEA to do kinematics, rather than using simple, rigid body kinematic relations. This seems like pure foolishness in almost all cases. Are we not developing a tendency to lean too heavily on the computer, rather than to learn to think as engineers?

 

I would be happy to hear some comments and discussion from others on these matters.

It seems what you are describing eludes to the fact that inexperienced young engineers tend to over-complicate matters at hand. The FEA analysis is a complicated means to an end that isn't necessarily justified for an 'initial' design effort. It makes sense if you are optimizing a design for one reason or another. If I were to advise young engineers on how to approach a design project, it would be to first seek out the guidance of experienced design engineers and the approach they take. Things aren't necessarily really complicated. The wheel has already been invented...

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"The Wheel Has Already Been Invented."

What a great comment! Absolutely true!!

DrD

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Simply put - the computer is GIGO system (Garbate In - Garbage Out) and if the person operating it - is not aware of what the computer does and why the results make sense or not - we can't have good designs. Especially if optimization is needed where more than one parameter is involved. 

A professor of mine said last semester that the computer is very dumb machine, it doesn't do anything by itself but rather we must tell it what to do. The advantage of the computer is that it does what it does very very very fast - and that's all we need to utilize. It can in no manner replace human judgement. At least not yet. 

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