# Physicist Needed

Discussion in 'Et Cetera, Et Cetera' started by TforTrapeze, Sep 29, 2006.

1. ### TforTrapeze Member

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Hello all LPSGers.
I need an intelligent physicist's help right now.
I am training in the circus arts and am attempting to build (instead of paying 1000+\$ to buy) a handbalancing stand.
it looks like that, but i'm only using two poles for now (i'm learning).
The poles are gonna be .5" in diameter (might have to be .7" i think, though)
They will be 30" tall, and 13" inches apart.
What is the minimum strength of the steel to make sure the metal won't flex or bend? Please try to make your explanation as understandable as possible. I did well in physics class, but don't go nerdy on me please. Thank you so much whoever helps me.

2. ### davidjh7 Gold Member

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You don't need a physicist--you need an engineer, preferably one with a background in strength of materials. Here is the thing---no matter what steel you use, at that diameter, it is going to have on the order of 100,000 PSI yield and slightly less that in tensile strenght. THe only real risk factor is in shear. TO remind you, the tensile strength comes from when you pul on it lengthwise. THe compression strength (also very high in this case) is when you try to push the ends together, like when you are pushing on the end. THe shear is the force that acts perpindicular to the long axis. Now, at that thickness, you aren't going to get much shear force, plus, the vector loads are still going to be mostly axial, and not in shear. If you look, the rods are actually quite a bit thicker than 0.5-0.7"--mostly, I suspect, to have some surface area to balance on. THey look more like 1.75-2.5" in diameter, as a guess. 0.5-0.7" would be a pretty bad stabbing force into your hands. If you got a regular carbon steel rod, at 2.5" in diameter, I suspect that you won;t have any problems with any kind of bending. THe most important factor here is that it be FIRMLY anchored at its base--prefereably bolted to the floor via a flange like is shown in that picture. If you need more specific information, I'd check for a copy of "Machineries Handbook" in the library, or failing that, at a decent bookstore in the engineering section. THat will give you the exact strenghts and specifications for a variety of steels. Good luck in your career!

Edit---looking again at the picture, you are right--the rods are likely less than an inch in doameter, but have a large cap on top. Until you can have a preffessionall, certified by an engineer, rod set, I;d still go for a 2.5" diameter steel rod, with a similar cap. In this case, for the training, the thickness of the rod isn;t really relavent--the size of the hand cap is.

3. ### roosevelt New Member

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I'd be seriously worried about liability.

I'm a profesional metal worker, and I'd seriously shy away from building that for someone, the risk is too great, and it won't be as cheap as you might think.

On the consideration that you're probably going to want to do it anyways....

I'd recomend 3/4" schedule 80 black iron pipe (weldable) as it's probably going to be the closest to the size you're looking for, and still strong enough to hold weight given some latteral load (a little flexing will occur, but the sch 80 shouldn't bend) weld everything solidly with a tig welder and 1018 tig rod, stress relieve the welds, and have them X-rayed. the base should be heavy plate, and pierced for the rods to slip through, and provide a secondary welding surface. (welded on the bottom, and along the top.)

So far you'll need a magnetic base drill, a tig welder, and proficiency as well as the materials.

I'll answer the question in more detail if you still feel you can tackle it with the minimums I've laid out so far.

4. ### davidjh7 Gold Member

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I guess this is one reason why I was thinking a much thicker rod, to really resist the bending moment----but thinking about it after your post, a 2-3" diameter schedule 80 black iron pipe, threaded, into a floor flange, and the floor flange bolted through either a very wide platform, or into a concrete floor, might do the trick---the strength of the large diameter pipe should resist a fair amount of bending moment, as well as provide a fair level of axial load. Obviously, nobody who does this for a living would think of taking on the liability of building it, only a professional circus supply outift, for \$\$\$\$\$\$\$---because of the liability involved. But something he can safely make himself, that is overbuilt to the nth degree, is better than him going off on something that will be questionable in strength. My two cents, anyway.

5. ### TforTrapeze Member

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keep in mind that the poles i am making need to fit a standard. Poles are between .5-.7" and yes, the blocks on top are about 3x5 and about 5/8" thick. The connections are threaded. And steel is the metal. Two companies providing this equipment are using inox steel and spring steel at .7" in diameter. So given those constraints, i'm sorry if i wasn't specific enough: is there a ballpark amount i can said is the "load" bearing capacity of the metal i order?

6. ### ClaireTalon Gold Member

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I gave this a bit of thinking (see attachment), and considered you being 6' tall at 170 lbs. Since I don't know exactly what steel you will use, I considered a maximum flexural stress that is average for all kinds of steel mentioned in the table. If you give me your exact height/weight, and material, I'll modify the calculation, if you want. But with these data I can say your weight should be supported by 0.6" diameter poles, or 0.7", if you want to be sure. However, you need a solid foundation for your construction, casting the poles into concrete would be the best option.

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7. ### roosevelt New Member

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"inox" is a generalization for any stainless steel of almost any grade, (term normally used in europe and parts of asia) this could be anything from 300 series to any of the cpm superalloy stainless steels. the alloy is impostant to strength and lateral load considerations, but the heat treating is also VERY important.

Spring steel is normally (in the US) 5160 1095 or 6150 depending on the application, any of these would be able to support the kind of stresses that you'd be putting them under, bot only if propperly heat treated. these carbon alloy steels are easier and cheaper to heat treat than the stainless varieties, but they are prone to rust.

Since you're talking about using steel that needs to be heat treated, I can understand the neccesity of having the rods threaded, (welding them would ruin the heat treatment, and leave you with brittle or soft uprights) but it would need to be a lathe turned machine thread, not a pipe thread.

After all the machining is done to the annealed steel, you need to have it professionally heat treated (yes PROFESIONAL, you screw it up, and you could end up impaled on one of them)

Unless you've got your own machine shop, and thermocouple controlled heat treat oven that can accomodate 30" rods, you'll have to hire all that work out, and by the time you're done, you're gonna be out almost as much money as buying one new, (maybe more) unfortunatly, this is something that's too potentially dangerous to comprimise on.

8. ### davidjh7 Gold Member

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Claire, your talents and sexiness continue to amaze and excite me.:biggrin1:

9. ### dolf250 New Member

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I am suitably impressed with the talent pool at LPSG. I now think that we could probably build our very own A bomb and become a world power with some of the people we have.
I was going to suggest schedule 80 and suggest that you find a pressure welder in your area. However, now I see that between Claire's telling you exactly what you need and Roosevelt telling you how you need it done I have nothing more to contribute (Aside from the idea of turning LPSG into a world power:biggrin1: .)

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10. ### BuddyBoy Member

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I can help with the uranium extraction and purification. Heavy water too, but that takes a while - have to start a fresh cascade. I'm no good with shaped charges, but I can do the "Little Boy" style, with the gun barrel shot of sub critical fissionable material, creating a single critical mass.

Low yield, but it would get some attention, I'd wager. :biggrin1:

11. ### roosevelt New Member

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just so happens that shaped charges are my specialty, but really, an A-bomb is so 8th grade science fair... lets do something really fun

12. ### davidjh7 Gold Member

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How about our own orbiting battle station? Controlling pesky annoying people is so much easier from orbit with a free electron laser and an atomospheric modulator......then, when someone types for the 11,000th time "I'm 11 years old, but posting as 18, and have a forty foot penis, is this normal?" Then, the sweaty fifty year old that actually posted said question...ZAP! instant atomization...what do you think?:biggrin1:

13. ### roosevelt New Member

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Now that sounds like fun

14. ### dolf250 New Member

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Finally a noble goal for all the minds at LPSG!

15. ### BuddyBoy Member

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Why don't we combine both projects and use atomic bombs to put the battle station in orbit, a la Project Orion? Yeah, ok, so there's a wee little tiny amount of fallout, but it's so much more efficient than a Hydrogen-Oxygen lifting platform.

16. ### Hatched69 Active Member

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I can provide the fuel. Tonight was brats and sauerkraut on the grill, and boy am I "fired up"!! Just got kicked out of bed, again... It must be bad this time. The wife's wearing her CPAP mask and she got wind of the fumes even through it....:biggrin1:

17. ### BuddyBoy Member

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Ewww, I wear a CPAP too and nothing is worse that getting a bad fart caught in your input filter and forced down into your lungs.

It's like Paris Hilton or a fart in a mitten: you know it's there, it stinks, but you can't get it out.

18. ### Hatched69 Active Member

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ROFLMAO!!!!

I think I may be in the doghouse for the next few nights. This episode was REALLY bad!! Even the cat and dog left the room....:redface: My wife just went to the bathroom with the dry heaves.... I'm such a bastard...:biggrin1:

19. ### BuddyBoy Member

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Well, at least you didn't throw the covers over her head and force her to prove she loved you by enduring a dutch oven.

20. ### Hatched69 Active Member

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That's already been done.... She caught on to that real quick. I think tonight was worse than anything she's ever endured before. I suspect there'll be paint peeling off the walls by morning light.....
I am SO gonna hafta kiss her ass for the next week!!!

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