Machinest Handbook lookup request (Pleeeeze)

I think this was posted recently a few times, if you check google it should turn up the answer for you.

Yeah it was Stu himself a week ago. Maybe time for you to get a book, eh Stu?

Todd L

Here ya' go, Stu:

3/4" iron pipe threads produce 32,450 ksi inverted shear strength. That is, assuming you've torqued the joint to a value between 86.5 and 86.6 ft-lb, backed off a half-turn, and re-tightened by 11/16 of a turn.

Enjoy!

Ed Huntress

Hmm. That sounds like a lot. Is this for the special 'nobendium' alloy?

Jim

================================================== please reply to: JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com ==================================================

Ed Huntress wrote: 3/4" iron pipe threads produce 32,450 ksi inverted shear strength. That is, assuming you've torqued the joint to a value between 86.5 and 86.6 ft-lb, backed off a half-turn, and re-tightened by 11/16 of a turn. ^^^^^^^^^^^^^^^ Ed, I looked in the index of Machinery's Handbook, and couldn't find this. So I turned all the pages, and STILL couldn't find it. I KNOW this will come up again, so I'd love to know to look for it. Please hurry. I'm holding my breath.

You can get at least 23.76% more than that if you use unobtanium pipe.

Jeff

You just don't give up, do you Stu?

Jeff

Even Better than that, if you fill the pipe with heavy water, its extra gravitational attraction will lessen the "pull" of the earths gravity by about .000258758 g/M/L. Note that if you put a resivoir above it, the larger you make it, the more you can hang from the pipe. To acheive the ultimate suspensive force, you must couple your resivoir to an ocean,... or at least one of the great salty lakes. You must use PVC pipe for this coupling though, or else the free gravitrons will adhere to a metal coupling pipe and you wont get anywhere.

mark

Yes, except that nobendium loses strength when you bend it.

Ed Huntress

It's written in secret code, right after the index.

Ed Huntress

Oh, well. That's no problem.

I'm not strong enought to do *that*.

:^)

Jim

================================================== please reply to: JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com ==================================================

In my 12th edition, it's written on the edge of the page, in green ink, where it can only read by those having a high moral tone and heroic studliness.

Kevin Gallimore

Group,

First let me apologize for posting my question more than one time. The problem was the Google was 'hiding' my posts and I repeated them because I believed that they were not posted. I asked Google to 'splain.

Why did I ask this questiion?

See my homebuilt elevator that 'hangs' on the threads of a single 3/4" black iron pipe.

Homebuilt Elevator

Thanks again,

BoyntonStu

They do that, down in the fine print they often say that 'some similar search results were omitted, click here if you want to see them' or something like that.

BTW if the machine is already built and works fine, why investigate the tensile strength issue now?

Jim

================================================== please reply to: JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com ==================================================

Hmm. Could I see it, if the studliness were 'amazingly excessive,' and not merely heroic?

Jim

================================================== please reply to: JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com ==================================================

And he wants us to register so we can watch 15 minutes of his dirty movies. I don't want any spam so I'm not gonna register.

Nor am I gonna register my gun

It looks very nice, Stu. About the strength issue: Pipe threads are made to seal against fluid leaks, and are nowhere near as strong as a straight thread, because first one wall (say, the pipe) and then the other wall (the fitting) tapers to a thin section. So you only have real thread strength over a short section near the middle of the thread.

Secondly, black iron pipe isn't spec'd for tensile or compression strength. It's spec'd on wall thickness, and, if you want to get fussy about it, it's the hoop strength (the strength against expansion of fluids inside) that's implicit in its specification. That, and allowance for corrosion, uneven construction, and ham-fisted plumbers.

Thirdly, even a straight thread on a hollow tube is a complicated strength issue. Thread strengths and standards are based on threading solid bar or rod. When you thread a tube, the standard strength calculations go out the window. Your minor diameter now is based on effective wall thickness as well as the depth of thread. There also is an issue concerning the tendency of the inner threaded piece to collapse from the angular forces imposed on it by the 60-degree thread angles. That's not an issue with bar or rod.

If you have to deal with calculated strengths, the first thing you want to do is to go to a mechanical tubing, rather than plumbing pipe. Then you'll have to consult someone who knows his stuff on the thread-strength issue for tubing. Either that, or use another method of assembly. You may actually have plenty of strength for the application with pipe-threaded plumbing pipe. But you won't be able to prove it, and, if liability is an issue, you'd be dead meat.

Good luck.

Ed Huntress

NPT threads are pretty much always sharp V form threads at the root of the male threads. This, along with the generally rough surface finish in black iron pipe, will cause failures to occur at the distinct stress concentration at the root of the threads.

I would suggest that the joints in question be static tested for, say, five or so times the static load they are expected to bear in use, to account for any dynamic loading they might see.

Jim

================================================== please reply to: JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com ==================================================

Google is not the best way to post to usenet newsgroups. I do know that it can be very slow to go from the posting to showing up in the database. There are many other ways to post which don't involve requiring a web browser to do it. It's strength is that it is a path to access things posted to usenet a long time ago, long after normal news servers have expired it.

Does this mean that you also haven't seen the various responses to your (several) postings? In short, the answer seems to be that steel pipe is not rated for structural use, and as a result, you won't find the information in any handbook. Steel pipe is too variable in multiple ways -- and the flanges into which you want to screw it are probably the weakest link of the entire setup.

Hmm ... I encounter the following message:

"Before you view images from Homebuilt One Person Elevator, you'll need to sign-in. If you're not already a member, now's the time to join. Why join? Because ImageStation is all about sharing. It's where you can store, edit, and share digital images, and it's all FREE."

Well ... I don't believe in giving some random imaging service my e-mail account (and perhaps other information), so they can spam me, so all I will see is the first image.

However -- I don't think that *I* would want to trust that assembly, from what I see of it in the one photo. Perhaps with machined threaded pieces from a known steel in place of the cast or forged floor flanges, and a thicker-walled pipe -- perhaps with straight threads, instead of the usual tapered pipe threads, it *might* be a bit safer.

If it is only you who is going to ride it, you know how it is made, and you can't sue yourself it if fails. If someone else is on it when it fails, you really have no protection from a lawsuit, without an engineering assessment of it from licensed professional structural engineers.

Good Luck, DoN.