how to make a wobbly floor!!!

[elveswillcom]

hi,
i am very new to this, and i would appreciate your insights.

i am planning a temporary art installation of wobbly floor which will last about 3 weeks.
the floor has to be 2.44 m x 2.44 m and around it, temporary walls and a door.
i want the whole floor to wobble as one sheet.
there will be more than 2 person on the floor at any given time.
this goes on top of a solid cement floor.

what material and method would be the best and cost effective for this project?
doesn't mdf tend to bend a lot?
i want it to not bend or sag so much because this will kill the wobble...

please help me!

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• elveswillcom
• 19 Apr 2011
• 1

 

[mointainwalker]

"there will be more than 2 person on the floor at any given time. "

Well I think if you want anyone to answer, you will have to specify a maximum weight because the difference between two people and eight people ( for example ) is rather a lot and will affect the answer ( if any ).

 

[RedHerring2]

I would think this is much more difficult than you first imagined.
MDF is definitely not worth a thought.
You're probably going to need, at least a steel framework, perhaps infilled with some timber, then covered in, at least 18mm ply or OSB. Bear in mind the sheets are 1.2m X 2.4m so think about the floor being 2.4m X 2.4m. Otherwise you'll need an extra sheet for the sake of an extra 40mm all round. But you'll need some clearance around the walls anyway.

The wobble is also going to be difficult. Perhaps one idea is to use a cut off end of a car propshaft, with the flange bolted to the underside of the floor and the 'tube' held in place with a slightly larger tube bolted to the concrete floor.

NB, your doors must open outwards otherwise they'll foul the wobbly floor. Alternatively mount the walls and doors on the edges of the floor, but that'll add a lot of weight.

 

[elveswillcom]

thank you all for your insights.

mointainwalker > good idea. i would need at least 2, because i want people to wobble each other out, and let's say maximum of 3 people.
so the maximum weight would be 250 kg.

RedHerring2 > i think steel frame is a good idea. ill ask metal works people about production and cost.

with the wobble, i was thinking of making a half sphere out of something (any suggestions?) and bolting that to the underside of the wobble floor.

the door will open outwards, but there is another problem:
i plan to have a step outside the wobble room so the step and the wobble floor is at the same level.
but when the floor wobbles, it will sink on one end and lift up on the other end, and if the floor lifts at the door end, it is a health and safety hazard for people entering. is there any method to overcome this?
i thought of hinging the floor on the door side, but i don't think this is the effect i am looking for: i want people to wobble each other out.

again, thanks so much for your helps!

 

[freddiemercurystwin]

So are you going to discriminate against fatties?

 

[mointainwalker]

but when the floor wobbles, it will sink on one end and lift up on the other end, and if the floor lifts at the door end, it is a health and safety hazard for people entering. is there any method to overcome this?

Two holes in opposing walls and then slide a suitably stiff piece of wood through to hold floor in level position.

 

[Static]

If your doing this on a shoe string budget then i would go with old car suspection springs in the corners and perhaps a trailer tow bar ball with socket in the center to give the pivot point..
Then a cross braced steel framework taking things to springs.. just make sure the socket in the middle is welded pretty solid or the whole thing may slide.

 

[RedHerring2]

I think Static's idea of springs in the corners is good, in order to slow down the reaction time of the floor a bit. Another alternative is a Land Rover front hub. There's a massive ball joint, about 200mm diameter IIRC, that might be suitable, with the wheel uppermost and the axle cut down and mounted on the concrete floor. That ball joint might have sufficient friction to reduce the reaction time of the floor.

 

[elveswillcom]

Dear all, thank you again for all your insights.

After consideration, I have decided that steel framing is not feasible with my time and engineering constraints.

I have made a little one at 1m x 1m with a 30cm diameter wooden dome stuck to it under the wobble floor and it seems to work.

I used 18mm MDF as the top board and 3x3 joists at 45cm.

1. Is 45 enough or should it be shorter?
2. 6 joists are running across 2 full sheets of MDF, and 3 noggins, 1 in the middle and 2 at 1/3 from ends. Does the floor need supports running ALONG the MDF sheets at the edges?
3. If it does, should they be noggins

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• elveswillcom
• 21 Apr 2011
• 1

or full length 3x3 in one?

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• elveswillcom
• 21 Apr 2011
• 1

4. If I joined up 2 of 1.5x3 with glue and nails to make a 3x3 and used them as joists, how much would that compromise the strength of the floor?

I hope it all makes sense, please refer to my drawings...
Thank yousss!

 

[RedHerring2]

A bit confused, you say you're making it 1m square, but your diagram shows 6 joists at 450mm centres???

I would put your joists at 400mm perhaps even 300mm centres, using 4X2, rather than 3X3, and I wouldn't use mdf, I'd use ply or OSB.

Two pieces of timber glued and screwed should be as strong as one piece.

And accross the end of the joists I'd use one piece not noggins.

Half-lap and glue the corner joints.

 

[elveswillcom]

hi redherring2,

the diagram was for the bigger one i will be making, 1m square is only an experiment, excuse my misinformation, but it was 3 am!
thank you for the information, very insightful with lap joints and i never knew that 2 pieces screwed could be as strong!

thank you, ill keep u posted!

 

[TheGayOwl]

Agree with RedHerring: lap joints, ply/osb, 4 by 2 and 300mm centres defo better. Anything less and it may wobble itself all out!

How much wobble is required? you initially thought of using tennis balls as dampers which I take as meaning the wobble to be a few inches??!!??

Also, is it planned to wobble in every direction? You could have it wobble like a seesaw which means you could have a simple pivot point and would also make your door issues go away as you could have door in middle adjacent to the pivot point.

My wife once constructed a 6ft long stiletto out of timber for her fine art degree. She then dropped out stating the course was too stressful...GOOD LUCK!

 

[mointainwalker]

My wife once constructed a 6ft long stiletto out of timber for her fine art degree.

Shoe or knife ?

 

[elveswillcom]

hi all, thank you so much for your supports.

mr gay owl> i think your idea about putting door in the middle is absolutely brillant!!! i am definitely considering it, although i originally thought of having it wobble 360. it solves the door problem perfectly. the wobbly will be about 7 cm, fingers crossed no one drunk falls and sues me!

now, i have some questions about springs.

1. with the car suspension springs, i have one concern. will it make the floor bounce and spring back really fast, when it is released?
2. i guess i should use a lower power springs since i don't want the floor to bounce back mad rapidly. but! looking on ebay made me even more confused since there are so many and without spring power information. could you advise on what kind of springs i should get?
3. once i get the springs, how does one fix them to the underside of the wobbly floor, since they are coil springs and springs are thin metal? or do i fix them to the concrete floor?

also regarding the wooden supports,
4. i would like to know whether screws or ringshank nails should be used, and bolts. do they have different uses?
5. how often should the screws/nails/bolts be put in?
6. since i am using 4x2 as joists, when i am joining joists with joists or joists with noggins, the nails have to be longer than 4 inches. what is the recommended length of nails for this?

i have so many questions, i hope i haven't bored you to death by now. look forward to your insights again, thank you!

 

[mointainwalker]

and springs are thin metal?

Springs with the power to move something like this with people standing on it are not going to be thin metal.

2

. i guess i should use a lower power springs since i don't want the floor to bounce back mad rapidly

I am not a specialist, but don't think it is primarily a factor of "spring power" how quickly the spring recovers: this is covered by a second unit which is a damper, once again as in a car. Working together the spring and damper control compression and recoil and without both, the system would be unusable.


When does this have to be ready ?