tower bolts

[Kansas Rust Buzzard]

I got a new old stock Fairbury Ranch tower, 40ft tall, marked 16 and 18ft mill. It is still all wired in the bundles and I think I got all of it other than the bolts. The stub tower was the only thing put together and it had 1 1/4 ungalvanized square head bolts in it. Each leg has three bolt holes on each end. My question, do I need to get better than farm store bolts for this? I think I can get farm store grade 5 but do I need to order grade 8? I am putting a 16ft Aermotor on it so I don't want to mess up here so just wondering if you guys think I should special order hard ones? Thanks for advice. Normally, my windmills are for display inside and I use pump jacks on wells so this big install is new to me. Thanks again.

[PaulV]

The primary load on the bolts is shear. A regular galvanized bolt (properly sized) is capable of a single shear load well in excess of the weight of the tower and 16' mill combined. Use standard hardware. Pretty much any bolt will be fine.

[Windcatcher530 Dan]

Aaron i think you'll be fine with grade 5 bolts like Paul said it's shear you have to worry about. And I don't think the original bolts Aermoter used were grade 8 because I've broke them taking towers apart.

[mtblah]

Thanks guys for knowing the engineering facts & terms how a bolt works ! and sharing that , from that I would guess fine thread & grade/diameter are factors for clamping determines?

[PaulV]

Thanks guys for knowing the engineering facts & terms how a bolt works ! and sharing that , from that I would guess fine thread & grade/diameter are factors for clamping determines?

The higher the grade, the greater the shear and tensile capability. Fine threads increase clamping force and permit precise setting of torque.

For our application, common zinc or galvanized coated course threaded hardware is more than adequate.

[Ron Stauffer]

If you want to replicate aermotor engenering, a 16 foot tower is 3 x 1/4 angle with 4 bolts on each lap that are 21/32. The shear strength of a bolt is dependent on how thick the metal it is in. An aermotor bolt being 21/32 has 10% more cross section than a 5/8 bolt. Aermotor bolts are either grade 2 or 3. There are civil engineering firms that could put a sdamp on your alterations for a slight fee.

Ron Stauffer
Montrose CO

[Kansas Rust Buzzard]

Thanks everyone. I know the tower isnt as heavy as Aermotor but I would assume the Ranch Spread design would be a bit better too? I am sure there is another one someplace but ai have not seen it?

[PaulV]

I believe your tower is up to the task. It's going to look great under that 16 footer.

[Kansas Rust Buzzard]

Yes, I kind of hate to cut it off to put the Aermotor stub on but I may not live long enough to find a Fairbury 16 or 18 ft. Anyway, she probably has been waiting since at least the early 1960s for a mill to go up there so its nice to see it finally used as intended. Thanks again

[Windcatcher530 Dan]

Thanks for saving another one Aaron. Please keep us posted and some pics !!!