Formula for wood breaking point

I'm building a climbing toy for my granddaughter and need to give some scientific assurances to grannie that the 1" dowels spanning 36" will more than adequately support her weight. Is there a formula to calculate breaking point based on weight?
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Yes, there are such formulas, but in reality, and in your situation, they're pretty much useless. Many variables, etc., etc.
Test the device yourself. There should always be a factor of safety of 3x or 4x - that's what they do on ladders, and what you're building is a ladder. If it can hold you, it can safely hold the grandkid.
R
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"Z3Driver" wrote:

-------------------------------------- Yes there is, but an even easier solution.
Take a look at a wooden closet rod.
Most are at least 1-1/8" dia.
Most are bent.
How heavy is the child?
I'd be looking at schedule 40 black pipe, at least 1-1/4".
Lew
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UPDATE: ------------------------------ "Z3Driver" wrote:

-------------------------------------- I previously wrote:

--------------------------------------- The 36" unsupported length is the fly in the ointment.
A ladder rung has an unsupported length of 12"-16".
Big difference.
Want to use smaller dia. rungs, add more supports.
Since the "styles" are in compression, not much material is needed.
Lew
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The rods might not be the issue - but the holder of the rods - stiles ? having holes within - being strong in the angle to the ground they are in.
Putting black pipe (galvanize can cut bare feet...) might be perfect but if the 'stiles' are not - the ladder will fail anyway.
Martin
On 7/7/2011 8:05 PM, Z3Driver wrote:

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On 7/7/2011 9:06 PM, Martin Eastburn wrote:

There is no need to drill holes in the uprights. There are pipe/rod holders of different diameters which can be screwed to the uprights to hold the appropriate diameter black pipe.
To the OP's question: there is NO way in hell I would use wooden dowels, of ANY diameter, in a 36" span for ANY child's "climbing toy".
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"Swingman" wrote

------------------------ All this talk of building "climbing toys", dowels, pipes, etc. bring back memories of the "children toys" my grandfather built for us kids. We lived with him for a couple years and when we were moving in, he decided we needed some kind of play set in the back yard. He built lots of pole buildings and had fallen some trees and debarked them. The had be drying out under a roof of an open pole structure.
He took these Poles, some of them at least 14" in diameter, and put them in big holes in the ground. They were packed with shale and pounded into a semi cement state. Two of the poles were at least 35 feet tall. By attaching some large planks across the top, this became the swing set. And by putting some more large poles in the ground around it, he created some gymnastic bars, monkey bars, ladders, etc. All were recycled pipe. He just drilled out holes in the logs, inserted the pipes and installed them in the ground.
The bottoms were treated with creosote, not done on children's toys now! These things went into the ground and stayed upright and solid for over thirty years. The original rope for the swing was good for over twenty years. It was only removed to add on to the house.
I should also mention that it snowed there and we used a big tractor with a blade on the front to remove the snow. This big playground set was right next to where we shoved the snow out of the way. So we had a huge snow fort next to the monster playground set. We would go nuts with that particular combination.
We live in a world full of pussy, wimp toys. No wonder the kids are turning out the way they are. Real, substantial toys built bodies and character! When I went to school from this environment, it was a country school where athletic shoes were unknown. We played soccer in logging boots. I was personally responsible for the death of several soccer balls. Damn, all this talk of my childhood is wearing me out!
Don't mind me. I am going back into my traditional curmudgeon mode now. <snooze>
Lee
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On 7/8/2011 11:12 AM, Lee Michaels wrote:

LOL ... I agree wholeheartedly, but ... and it's a big BUT.
There were fewer LAWYERS in our less litigious childhood, and even most of those lawyers (and parents) back then had old fashioned values and common sense.
With regard to lawyers, it is a dead certainly that is no longer the case.
It's not so much what you do for your kids/grand kids, it's their friends, or their kid's friends, who will be using your kids/grand kids homemade toy ... and guess who gets sued.
It happens on a daily basis.
AAMOF, just turned down a nice, and normally potentially very profitable, cabinet job - some Tansu cabinets (like the kind I built for my office on my website) for a kid's play area in their home - uh huh, NOT me!
I'm sure I could figure out a way to keep it from tumbling down when their kid, or one of his friends, decided to climb Mt Everest in the playroom, but by that time it would be way over the budget, and with no guarantees.
30 years ago I wouldn't have hesitated. Unfortunately, it's the times we live in ....
Didja get that puppy yet? Pictures if you got'em. :)
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WIMP!! :-)

Another week. I still have to puppy proof the fence.
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On Jul 8, 12:12pm, "Lee Michaels" <leemichaels*nadaspam* at comcast dot net> wrote:

When I was a kid, I had to walk 5 miles to school in the snow, both ways up hill. JoeG
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Yeh, barefoot, too, with barbed wire wrapped around your feet for traction.
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<http://www.engineeringcalculator.net/beam_calculator.html
You'll need a moment of inertia
<http://www.engineeringcalculator.net/cross_section_properties.html
And you'll need the elastic modulus for the wood
<http://www.conradfp.com/pdfs/ch4-Mechanical-Properties-of-Wood.pdf
Or make up a sample and see how much weight it takes to break it.
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On 7/7/2011 8:05 PM, Z3Driver wrote:

I wouldn't, suppose a bigger kid gets on it. Suppose she slips and falls down to the next step and dowel breaks with a sharp pointy end sticking out. At the very least run a support through the center and use a larger dowel.
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Granny is smart. Little boys kick at things like that, jump up and down on them, etc., so your granddaughter might climb up a ruined ladder some day and pay for it.
See if these help. (I didn't review them.) http://www.worldwideflood.com/ark/design_calculations/wood_strength.htm http://www.fpl.fs.fed.us/documnts/pdf2001/green01d.pdf
P.S: I'd put a stiffener in the middle so the dowel only had a 17" span. Then they might support adults, too, especially if they're oak, ash, or hickory dowels.
http://www.midwestdowel.com / http://www.atlasdowel.com/pages/products/default/5 / http://goo.gl/7NDWa by the hundred (Ouch!)
-- Happiness lies in the joy of achievement and the thrill of creative effort. -- Franklin D. Roosevelt
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On 7/7/2011 8:05 PM, Z3Driver wrote:

Thanks for all the quick replies. I think Leon and Larry offered some good advice to add a stiffener in the middle. Looks like my Forstners are going to get a good workout this weekend.
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