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Pivot for tilt up three-sided tower | 15 comments (15 topical, editorial)

Re: Pivot for tilt up three-sided tower (3.00 / 0) (#2)
by vfarrell on Sat Aug 9th, 2008 at 08:01:42 AM MST
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Hi Ed

What is the estimated weight and height of the tower? (thinking of the pending forces you will be applying to those two legs on the tower and the pivot rod itself during the raising of the tower)

also what is the dia of the steel dowel you used in your pivot?

"Everybody's got to believe in something. I believe I'll have another beer." --W. C. Fields
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Re: Pivot for tilt up three-sided tower (3.00 / 0) (#3)
by vfarrell on Sat Aug 9th, 2008 at 12:21:23 PM MST
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opps sorry missed the part about 5/8 rod my bad..
"Everybody's got to believe in something. I believe I'll have another beer." --W. C. Fields
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Re: Pivot for tilt up three-sided tower (3.00 / 0) (#4)
by elt on Sat Aug 9th, 2008 at 12:23:22 PM MST
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Hi Vic,

I figure the tower weighs a little less than 100 pounds and the mill and pipe on top of it are another 100 or a few pounds more. The tower is 24 feet; the mill with be up another 6 feet on the pipe. The tower will be bolted to my workshop about 12 feet up.

The steel pivot rod is 5/8" diameter. What I was thinking was that most anchor bolts I've seen were 1/2" or 5/8" so I figured (guessed) that the pivot didn't have to be any bigger...

Comments are appreciated!

Thank you,
- Ed.

[ Parent ]

Re: Pivot for tilt up three-sided tower (3.00 / 0) (#5)
by TomW on Sat Aug 9th, 2008 at 01:07:37 PM MST
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Ed;

I think the forces on the hinge in a tilt up are enormous. Much more than any static load while in place. I am no good at math but if you ever tilted something up from horizontal you would see how much pull it takes and it all gets amplified into the hinge.

My 30 foot 4 leg tower that I tilt up uses a 5/8 hard bolt in each leg of the hinge side as a "pin". It has a 10 foot dual rotor similar to those built by DanB. I would not even consider anything less. You can see the flex in the 3 inch angle iron legs and embedded connections to the footing when it is just coming to rest or just being lifted off horizontal. The shearing forces on the bolts must be a couple tons in my set up. There are forces at work here that are not immediately obvious.

Bigger is better, IMHO.

Just from here.

I also never stand near the base when I am lifting in case something fails I want to be well beyond where it can get at me.

Good luck with it.

Tom

"Education consists mainly of what we have unlearned."--Mark Twain
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Re: Pivot for tilt up three-sided tower (3.00 / 0) (#7)
by elt on Sat Aug 9th, 2008 at 07:45:19 PM MST
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Hi Tom,

I looked at your towers in your gallery; thanks for putting them up. I'm quite jealous! I'd really like to go with a four-sided wide-base tower. I understand their structural advantages but for now I have to go with what I have.

You wrote:

> I am no good at math [...] The shearing forces on
> the bolts must be a couple tons in my set up.

I'm pretty good at math if I do say so myself. My problem (not being a mechanical or civil engineer) is that I don't know what formulas to use, what the numbers would mean if I got an answer, or what's "standard" or "code" even if I knew what I was doing...

So, I've done some math but whether or not it means anything or not I'm unsure:

My math says (conservatively) that the 5/8" rod has a shear strength of about 8000 pounds. Lifting the tower up can't generate that kind of force but a 250 pound sideways force at the top of the tower while it's being lifted could. But the weight of the tower and mill could only generate half that force. That 2x safety factor combined with the conservative rating of the rod gives a safety factor of about 4x. I might want a higher factor in a public setting but I think (guess) that that's enough for my backyard. Well, that's if my engineering is worth the pixel dust you're reading...

> You can see the flex in the 3 inch angle iron legs [...]

It's possible that my tower is stiffer. I haven't seen any tendency for it to flex yet.

Also, I don't think that the weight of the tower and mill (also a 10 footer) will flex the rod because the rod is supported along it's entire length and range of motion directly on the concrete.

If you can imagine that the following drawing is an end-on view of the bracket, then it shows the tower and bracket at 0, 30, 60 and 90 degrees.

This is the main reason that I didn't put the rod into a hole drilled into a stationary piece of metal, then I'd have to wonder about the strength of that piece as well. But since it's not there, it can't fail!

Well, that's my thinking-slash-design-strategy. I'm not saying that stronger isn't stronger but that would still leave me with the question of what's good enough.

Thanks again,
- Ed.

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Re: Pivot for tilt up three-sided tower (3.00 / 0) (#6)
by vfarrell on Sat Aug 9th, 2008 at 04:13:33 PM MST
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If it was mine I'd beef it up a tad, and recommend guy cables at the top.
safety 1st bro

imho

-Vic

"Everybody's got to believe in something. I believe I'll have another beer." --W. C. Fields
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Re: Pivot for tilt up three-sided tower (3.00 / 0) (#8)
by elt on Sun Aug 10th, 2008 at 05:47:52 AM MST
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Do you mean temporary guy wires while raising it? I think that I have clearance in my yard to do that and that would minimize the risk of a sideways force damaging anything while the tower is being raised.

Thank you,

- Ed.

[ Parent ]

Re: Pivot for tilt up three-sided tower (3.00 / 0) (#9)
by vfarrell on Sun Aug 10th, 2008 at 11:07:24 AM MST
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I would At least While raising the tower, as permanent part of the tower couldn't hurt if you have feasible anchor points on the ground to do so.

Vic
"Everybody's got to believe in something. I believe I'll have another beer." --W. C. Fields
[ Parent ]

Pivot for tilt up three-sided tower | 15 comments (15 topical, 0 editorial)

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