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
Reply to
djenyc
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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
Reply to
Ed Huntress
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
Reply to
Doug
If a forklift crumbled when lifting your dad, maybe he should lose some weight.
When I was building my trailer
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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
Reply to
Ignoramus2150
Ed Huntress sezz:
Good point. The book example I gave was used at a college in the mechanical engineering technology cirriculum. -- Doug
Reply to
Doug
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. :)
Reply to
djenyc
I cannot find the link, I thought I had it. It is a deflection calculator from some mechanical society...
i
Reply to
Ignoramus2150
Doug, thanks for the book info.
So far I've found a lot of good metalworking books in pdf format on
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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
Reply to
djenyc
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...
Reply to
djenyc
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
Reply to
Ed Huntress
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
Reply to
Ed Huntress
You might want to look at Harry Parker's "Simplified Design of Structural Steel" and "Simplified Design of Structural Timber"
Kevin Gallimore
Reply to
axolotl
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
Reply to
djenyc
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
Reply to
Ed Huntress
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
Reply to
Karl Townsend
There's the voice of wisdom. I do the same thing.
-- Ed Huntress
Reply to
Ed Huntress
How do you know that whoever built the article you are copying actually spent time designing it?
When I was doing design work, the first thing I did was go to the tech library and see what others had done. But you need to run a few calculations before deciding to use some one elses design.
Dan
Reply to
dcaster
I don't. Maybe he copied it, too.
But I'm talking about hobby things, not production. For example, I made a fly reel around 20 years ago (*far* more effort than it was worth), and I just copied some of it from one I had. Same for the oscillating steam engine I made. It probably was a 10th-generation copy.
If I ever build a bridge, I'll keep that in mind.
Actually, I agree. I considered building a spaceframe sports car five or so years ago, and I even got a simple FEA (Cadre) to analyze others' designs. (Many commercial frames suck in a big way when you analyze their torsional stiffness.) Then I got so caught up in studying and analyzing chassis design that I never built one. d8-)
-- Ed Huntress
Reply to
Ed Huntress
For your type of use I'd recommend something like Architectural and Engineering Calculations Manual (Hardcover) by Robert Brown Butler # Hardcover: 464 pages # Publisher: McGraw-Hill Companies (August 1983) # Language: English # ISBN-10: 0070093636 # ISBN-13: 978-0070093638
In spite of the broad sounding title, it has sections on sizing steel beams, wood beams, pull out strength of screws, etc etc. And the other sections talk about lighting levels for your shop (or whatever), pipe sizes, etc etc. No theory, just formulas for what you need.
djenyc wrote:
Reply to
RoyJ
I also get caught up in studying and analyzing and often don't ever get around to doing any actual building. The things that I design and don't build always are perfect. The things I actually build often are not prefect.
Dan
Reply to
dcaster

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