Mechanical Enginnering for Dummies - any suggestion on design making? Load ratings for common wood and steel materials like 2X4s etc

Hi, I'm doing some hobby level wood and metal fabrication projects around house - shelving, boat cradle/ boat lift / trailer implements/
carts / work tables/ bike racks etc. I'm mostly using scrap material that I happened to come buy...
I'm not a mechanical engineer, and have no idea what load/deflection ratings are for different materials. I've been using 2x4, steel tubbing, angle iron ... just found 20 ft of 2" pipe another day :) ... Currently, when I'm designing stuff, I just rely on limited prior experience and eye measure. Some things turn out to be overbuilt and sometimes things fail under load (hopefully it's not critical and I get a chance at redesign :)). For example, I built a manual forklift last week and it crumbled while testing/lifting my dad - now I know where to strengthen it :) , but is where a better way?
Would it be worthwhile to look up load ratings of common materials like steel pipe and 2x4? Where would I find such information? Or are this calculations so complicated, that I'd be better off continuing with what I'm doing?
For making plans I'm currently using Vectorsoft Draw - a 2-d drawing program on PocketPC and experimenting with Google Sketch-up for 3-d drawings. Move away from paper a couple years ago. Would like to hear comments on what else is good.
Are there any good books for home-workshop design /plans making? - just basic practical stuff that can be readily applied, not looking for Mechanical Engineering intro course
Thanks a lot
Ross
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It would be worthwhile, but if you're not building anything that risks life or limb, learning by trial and error isn't bad, either.
For the examples you give there are two basic subjects you need to know: strength of materials, and "statics." If you want to learn them, be sure to use texts written for technical schools and junior colleges, not for four-year engineering-school students. The former explain it in terms of high school algebra. The latter do it in terms of calculus. If you're good at calculus, use either one.
A basic study of these subjects will not make you a design engineer but it may prevent some of the grosser errors. And you may find it very interesting. These subjects provide a lot of suprises and insights into how things work -- and how they don't.
I'd call a local community college and see if they have a program in "engineering technology," or something like that, and ask what texts they use.
-- Ed Huntress
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Ed Huntress sezz:

Good point. The book example I gave was used at a college in the mechanical engineering technology cirriculum. -- Doug
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Ed, thanks, I'll check on what books they use at community college. I went to community college a while ago before transferring to university, and found they courses to be more entry-level and application oriented/ vs. more theoretical/fundamental stuff at 4 year school. It is odd though that there are a lot of free books on line (US Navy/Army, expired copyright, farming books, etc) about metalworking, welding, drafting, quality control, fabrication, but nothing on design... Even non-free selection seem to be more production and college oriented...
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Yeah, that is interesting. I never looked online. My own books on those subjects are ones I bought decades ago, so I can't help you with titles.
I'll tell you what I do when I want technology books like that, though -- particularly for construction trades, welding, landscaping, etc. I find out what the local community college is using and then I go look for them in their library. Then I come home and order them on an interlibrary loan through my local community library.
That is, for books I don't want to keep. I'm very cheap. d8-)
-- Ed Huntress
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Just on the off chance that this one is still around (these texts often go through many editions), the basic one I use is _Statics & Strength of Materials_ by Bassin, Brodsky, and Wolkoff. Mine is the 2nd edition, 1969, McGraw-Hill.
It should be ideal for what you need. It even includes tables of properties for many materials, including different types of wood. But those are easy to find on the Web. And don't forget to ask here. There is a wealth of such information in the heads of the members of this NG.
BTW, if you *really* want to know about wood, there is an excellent and enjoyable book titled _Understanding Wood_, by R. Bruce Hoadley (I hope I have the spelling right). This is no text -- it's written for the hobbyist -- but I hear it's used in technology classes, too. It's published by Taunton Press.
-- Ed Huntress
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Thanks Ed! My local library has great online feature - I can look for books including inter-library loans from other libraries and make a loan-request online. Saves me an extra trip and time. And they call me up when the book is ready for pick-up, usually takes them 3-5 days. I actually just found and put in a request for Statics & Strength of Materials - 1988 edition and located Understanding Wood at the local library. Will check them out.
Ross
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Oh, that's a good deal on interlibrary loans. I have the rest of that, but they make me come in for interlibrary stuff.
Well, happy reading. You'll only need some parts of _Statics..., which you'll recognize, but you may wind up reading through _Understanding Wood_. It's a classic.
-- Ed Huntress
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My library does this also, works out great since we homeschool our kids and frequently need all kinds of reference books. Nothing like getting online with a list of recommended books for whatever the curriculum we are currently using, be able to get them from just about anywhere in the state and have them delivered to our local branch. Only thing better would be if they could deliver them directly to our door, then again that would negate the weekly trip to the library for the kids and in my opinion nothing beats wondering around a library as you never know what might catch your fancy.
Bill
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http://www.woodweb.com/knowledge_base/Wood_Handbook.html
I'm not sure how this compares to what you mentioned, but its free and looks very technical. I've browsed a few sections in the past.
"Wood Handbook -- Wood as an Engineering Material Information on engineering with wood, properties of wood and designing with wood. September 28, 2002"
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wrote:

Oh year, the Forest Products Laboratory book. Also excellent, although aimed more at the engineer. I have a really old copy of it that I have referred to in the past.
Hoadley's book is more for the amateur who wants a good understanding of wood as a furniture and building material. I think Hoadley is an engineer himself, and an academic, but he takes the point of view of a hobbyist. At the same time, the book is very thorough and provides a lot of information about dealing with shrinkage and expansion, etc.
It also contains excellent information on identifying species of wood from any old plank you have lying around (You need a 15X hand lens). For me, that alone makes it worth the price.
-- Ed Huntress
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Ed Huntress wrote:

I took a quick tour of all the 1st-level answers to the OP's question, and this is just about the best one, and the one that I'd recommend if such a book exists in the area you need to know.
You may even consider going to said community college and taking the class, if you have time. This will be particularly useful if you can buttonhole the instructor and ask questions about specific projects you're working on -- you'll get a design review of something you care about, and information that pertains directly to what you're doing.
--

Tim Wescott
Wescott Design Services
  Click to see the full signature.
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djenyc sezz:

Look for an engineering school macine design book. It will have good references for the section modulus of various shapes and materials as well as the simple formulas for calculating beam deflections, etc.
One example:
Machine Elements in Mechanical Design Mott, Robert ISBN: 0130618853 Publisher: Prentice Hall, Lebanon, Indiana, U.S.A. Publication Date: 2004
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Doug, thanks for the book info.
So far I've found a lot of good metalworking books in pdf format on http://www.metalwebnews.com/ed.html . I've been reading Farm Shop Practice, US Army - Fundamentals of Machine Tools, US Navy - Machinery Repairman Handbook, US Army - Welding Theory and Application, Aussie Weld - The Welding Tutorial. That and some books from local library and through inter-library loans. They were easy to read, but none went in to design details. On the other hand, books on mechanical engineering that I saw in local library were written for college courses, while I was looking for a few hundred pages farmer series type booklet :). A problem with college course, imho - an overview course will not go in to enough details to be of practical use, and detailed courses go too far in to theory/formulas and procedures applicable to industrial production ...not ballpark figures for hack- jobs I'm in to:) I mean, may be I'm wrong, but the stuff I saw at the library was just scary
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If a forklift crumbled when lifting your dad, maybe he should lose some weight.
When I was building my trailer
http://igor.chudov.com/projects/Homemade-Trailer-With-M105A2-Bed/
I use a online deflection calculator. I think that while in general, engineering steel structures requires a lot of expertise, engineering severely overbuilt structures requires a little less expertise.
i
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wrote:

I needed that forklift to carry ~150lb load, not industrial size:) The part that folded was made from remains of 12 gauge mower decks ... running low on materials at the moment :)

Cool, do you have a link for that calculator. I wonder how 2x4's compare to black pipe... I'd like to overbuild, but I have a lot of ideas and not a lot of steel. :)
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I cannot find the link, I thought I had it. It is a deflection calculator from some mechanical society...
i
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djenyc wrote:

You might want to look at Harry Parker's "Simplified Design of Structural Steel" and "Simplified Design of Structural Timber"
Kevin Gallimore
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I got an engineering degree 30 years ago. promptly forgot all of it.
My design criteria has always been to find something about like what I'm building and copy it. "Shamelessly Plagiarized" is the term I use. Its worth it do drive a ways to find something like what you're doing. Some poor engineer has spent days designing that part, take advantage of his time.
Karl
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There's the voice of wisdom. I do the same thing.
-- Ed Huntress
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