Egg/Ball Chair thoughts, design help needed

[rollerboi]

Heya, folks. I've always been interested in the egg chair, designed by Eero Aarnio.
We've all seen it in both of the Men In Black movies..

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We also see the egg chair make an appearance in the Prisoner series.

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The designer says, "I made the first prototype myself using an inside mould, which has been made using the same principle as a glider fuselage or wing. I covered the plywood body mould with wet paper and laminated the surface with fiberglass, rubbed down the outside, removed the mould from inside, had it upholstered and added the leg."

I'd like to make one for myself, with modifications. However, I'm concerned about the structural support aspect of the single-stem base and the chair itself. It appears as though the original designer constructed a mold around which the fiberglass was covered, and then took the mold out, leaving behind only a fiberglass shell. How, then, would you recommend constructing a smooth egg or ball-shaped plywood frame?

Will the fiberglass be strong enough to support the weight of someone sitting in it? I weigh about 210 myself. Are there any specific techniques that anyone could recommend for me to look into?

Also, I am concerned about the stem, or base of support. I've seen a number of people posed in the chairs, some sprawled out, others shifted to a side.. what should I be doing with the base in order to ensure stability? Is there a calculation, a formula that will tell me the minimum necessary thickness for the stem and the flange?

Thanks a bunch for any help, ideas, or comments that you could add to this project. Links to tutorials would be more than welcomed, as well.

 

[Mike Rush]

A couple of quick ideas based purely on my own meandering experience...

Not sure about the best way to buiold the wooden former, sorry. :confused

However, to answer your other questions: once you have your hollow fibreglass egg, as far as I can tell there's nothing to stop you reinforcing the inside. The upholstery will cover a multitude of sins.

One way to do this would be to use paper rope, which you get it from fibreglass suppliers. It's a paper rope (obviously) with a wire down the middle, meaning that you can bend it to any shape. You form it to the inside of your egg, and then laminate more fibreglass over it. The rope doesn't add any sturdiness, but what it does do is make hollow ribs in your fibreglass, which give it more strength than extra layers alone would.

As for the base, what I learned at school was that any object will remain standing as long as its centre of gravity is somewhere above its footprint (base). So if your base was the same diameter as the egg (for example), someone could happily sit inside in any position they wanted, and never tip over. The only danger would be if they extended their feet out of the egg; but since the majority of their body weight, plus the egg itself, would still be over the base, it shouldn't be a problem. In practice I think the base could be smaller than the egg... but to know exactly how much you might need to do some maths. Or some trial and error.

 

[eltee]

You may want to look at the various egg chairs commercially available to see the bases. They seem to have short, broad bases to prevent toppling. The ones for sale look comfy and cozy esp. the ones with built in speakers and tactile transducers. I also noted they sell the shorter, ball chairs.

 

[clonesix]

I wouldn't sweat the base. If you were to cut the top off the egg, you wouuld be left with an ordinary chair. All the base needs to do is support your weight and have a wide enough base to prevent overturning.

IMO, it would be cheaper to buy the chair rather than make one from scratch.

If you do want to take this on for whatever reason, here is how I would do it: make a female mold to laminate fiberglass into. (if I had pictures this would help)

The egg is symetric about the Y axis, so build a template of half the egg about the Y axis. A template is made of 1/2" plywood with with a piece of pipe running the length of the Y axis. At the outside edge of the plywood is cut to the egg profile minus 1/4". To the edge of the template, you will need to attach some sheet stock to extend beyond the plywood for the final egg profile (doesn't matter if its sheet metal or plexiglass or masonite) to act as a cutting surface.


Now for the mold. You build plywood form in the rough shape of the egg minus 1". Give it some ribs and blocking. Make it strong enough to carry the weight of 50 lb of plaster. Once you have a rough egg shape, line inside with wire mesh and staple in secure to the inside. Add enough burlap so as to hold the plaster.

Your mold also needs to supports the template you made in step one. A couple of hole downs on the Y axis to hold the pipe firmly, but allow it to pivot freely.

What you should end up with is a 3 dimensional half-egg "bucket" with 2 dimensional "blade" free to pivot within the bucket with 1/2" tp 3/4" space in between them.

Now mix up a big stiff batch of plaster and spread it inside the egg. It should be held in place by the burlap and wire mesh. Now sweep the template through the fresh plaster. You will see that you have cut the shape of the egg. There will be some hollow areas where the template didn't meet the plaster. Just add more plaster to the vacant areas and keep pivoting the template back and forth as the plaster begins to set. As the plaster sets, the template will cut a cleaner and cleaner path as it pivots, until you are left with a smooth concave egg shape.


That's a lot of work for one chair, but you will end up with a half egg mold. You will need to sand the inside smooth and seal before laminating glass into it.

Well, that's how I would make a large egg if I couldn't just buy one.

After you make the one egg, what will you do with the mold that you spent all that time on?

Does this make any sense without pictures?

 

[rollerboi]

Thank you for your very detailed answer on the egg chair. I was hoping to be able to build one at a fraction of the cost that it would take to buy, so if the cost is going to outweigh things, then I'm not going to go through with it, sadly. I can't justify that to the wife, who's not so hot on the idea in the first place.

Your description does make sense, sounds like i'd be basically reverse-lathing an egg-shaped mold.

In my original thoughts, I was thinking of making a spherical (internal) frame, adding a barrier between the frame and the fiberglass, then just laying down layers of glass to build up the shell. Once it sets to a suitable thickness, I'd disassemble the frame from the inside. Would that open me up to risk of surface irregularities, or just too thin of a fiberglass wall?

Would that approach be cheaper?

Would I do better to carve it out of foam and coat the surface?

Also, as far as the base is concerned, I'm not as concerned with the chair tipping over as I am with it breaking off its stem.

 

[gnrlotto]

Aren't these chairs also used by Sarah Jessica Parker in Mars Attacks.?

 

[clonesix]

Yes you can carve it out of foam and glass over it. The quality of the egg will depend on the smoothness of your final shape and your skill at fiberglassing. After the egg is fiberglassed, you will still need to bondo it smooth.

Between the foam carving, and Bondo sanding, it is going to be pretty messy around the house for up to 6 months.


Buying a chair looks pretty appealing right now to me. I am no chair expert, but there has to be one on ebay or some scap yard somewhere. It can't be that rare and unobtainable.

People on this board can find a piece of plastic the size of a quarter that hasn't been in production since 1977. Someone ought to be able to locate one egg chair. Put them on the job.

Good luck

 

[SFPROPS]

These chairs are widely available. It's not hard to track one down. You're going to spend at least $1,000 on one though.

 

[clonesix]

$1,000 ??? Actually, that is cheap compared to the chairs I found on a google search http://www.sixdifferentways.com/gallery/becg

It is time for plan B : Just keep feeding your pet chickens hormones