seesaw bearing for adult-sized seesaw

Hello

Apologies in advance for cross posting - and for asking such a basic question:

I'm wondering if any of you out there can help me. I'm building a sound installation that you control by moving up and down on a giant seesaw. Ideally, I want the arms of the seesaw to be very long - say,

5m long each side of the fulcrum. And I need the seesaw to safely carry a 95-percentile adult at each end (so that's someone who is 110kg). Trouble is, I need some help with the practical side of the mechanical engineering. I'm trying to figure out the best way to make a seesaw that can safely meet these requirements.

My main concerns are:

- The bearing. I live in the UK. Can any one point me in the direction of a company who could supply a bearing that could take these sorts of moments, moving a seesaw speeds? I'd like to spend as little as possible on it.

- The beam. What material would you recommend? Tubular steel? What thickness of variouls solid woods would be required? Is there a formula I can use to work out what thickness of material can take this much strain, given certain material properties?

...sorry if these are all stupid questions but I really am not very up on these matters and I want to make something that can take the strain.

Any help gratefully received!

Sarah

Sarah,

If you can order steel I-sections there by the same names as used here , an I-beam called an S6X12.5 would suit your purpose, with a wooden plank fixed at each end on top for seats. The max deflection of the 33.5 ft beam would be around 5 inches at each end with the 250 lb subjects. This is an I beam that is 6 inches deep and 3.3 inches wide that weighs 12.5 lb/ft. The second moment would be 22.1 inch^4 The fulcrum might be fabricated from 2 inch diam steel tube and cast iron end fittings sold for guard rails. The cross tube fulcrum might be welded to the I beam and allowed to rotate in the cast iron fittings. The cross tube could be bolted to the I-beam by side flange sockets sold for guard rails as an alternative. The verticals would be attached to base flanges bolted in a concrete base.

Regards

Brian Whatcott Altus OK

Thanks very much for the advice Brian. I'm going to send your spec to a few local companies. And if I manage to make this seesaw, I'll send you a link to a photo!

Best wishes

Sarah

On 2007-04-27, 17:11 Z, in news: snipped-for-privacy@r30g2000prh.googlegroups.com, Sarah wrote (paraphrased):

Sarah: Assuming a dynamic amplification factor of 2.0 and a yield factor of safety of 1.67, you could use an I-beam made of mild steel, grade S235JR (possibly called grade 40B in UK), with tensile yield strength Sy = 235 MPa, and size designation IPE 160 A in Europe (possibly called 157 x 82 x 13 in UK). This I-beam would have height 157 mm, width 82 mm, flange thickness 5.9 mm, web thickness

4.0 mm, moment of inertia Ix = 6890000 mm^4, torsional constant J = 19300 mm^4, and mass per unit length 12.71 kg/m. This beam would have a mass of 127 kg. The vertical deflection at each end of this beam under static loading would be 39.7 mm.

Alternately, you could use an aluminum I-beam having the same dimensions listed above, which would have a mass of 44.0 kg. Vertical deflection of this aluminum beam under static loading would be 102 mm.

The fulcrum rod, made of mild steel, should pass through the neutral axis (center point) of the I-beam web and also through fittings bolted to each side of the web. Do not bolt nor weld these fittings to the I-beam flanges. If the fulcrum does not pass through the I-beam neutral axis, then you would need to let us know, because the above beam size would no longer apply. The fulcrum rod, of solid circular cross section, and of length not exceeding approximately

110 mm, must have a minimum diameter of 28 mm, but you can make it 30, or even up to 40 mm diameter if you wish.

On 2007-04-27, 17:11 Z, in news: snipped-for-privacy@r30g2000prh.googlegroups.com, Sarah wrote (paraphrased):

Sarah: Assuming a dynamic amplification factor of 2.0 and a yield factor of safety of 1.67, you could use an I-beam made of mild steel, grade S235JR (possibly called grade 40B in UK), with tensile yield strength Sy = 235 MPa, and size designation IPE 160 A in Europe (possibly called 157 x 82 x 13 in UK). This I-beam would have height 157 mm, width 82 mm, flange thickness 5.9 mm, web thickness

4.0 mm, moment of inertia Ix = 6890000 mm^4, torsional constant J = 19300 mm^4, and mass per unit length 12.71 kg/m. This beam would have a mass of 127 kg. The vertical deflection at each end of this beam under static loading would be 39.7 mm.

Alternately, you could use an aluminum I-beam having the same dimensions listed above, which would have a mass of 44.0 kg. Vertical deflection at each end of this aluminum beam under static loading would be 102 mm.

The fulcrum rod, made of mild steel, should pass through the neutral axis (center point) of the I-beam web and also through fittings bolted to each side of the web. Do not bolt nor weld these fittings to the I-beam flanges. If the fulcrum does not pass through the I-beam neutral axis, then you would need to let us know, because the above beam size would no longer apply. The fulcrum rod, of solid circular cross section, and of length not exceeding approximately

110 mm, must have a minimum diameter of 24.5 mm, or a maximum diameter of 28.5 mm.

On 2007-05-07, 13:14 Z, I wrote news: snipped-for-privacy@e51g2000hsg.googlegroups.com.

I retract my previous post, referenced above.