Round Table question - An Update.

[Zeddedhed]

I've been asked to make a round table for a client who is wheelchair bound. He wants it made a little higher than normal table height so as to be able to get his wheelchair under the table whilst sitting at it. The table is to have a diameter of 1m and a single middle leg with three or four feet.

My question is this:

Is there a known proportion or formula that ensures a stable table that gives diameter of top, height and "diameter" of bottom feet?

I want to keep the underneath as compact as possible to ensure that it's comfortable for him to sit at whilst ensuring that it remains nicely stable.

 

[Steve Maskery]

If there is, I don't know about it. But I have made a few round pedestal tables and I can tell you this.

Although slightly more difficult to make, though not much, a 3 legged table is more stable than a 4 legged one. It never rocks.

However.

You might be tempted to line the ends of the feet up with the circumference of the table. This is too small. Each pair of feet can form a fulcrum on which the table top can tip. And if it can tip, it will tip.

So draw the diameter of your table top and then draw a triangle around it. If the points of the feet match the points of the triangle, the table cannot tip unless it is physically lifted. Of course, the downside of this is that the feet stick out more and that might be an issue with anyone, let alone a wheelchair user.

Probably a compromise between the two, but closer to the full triangle, especially as this is a higher-than-normal table.

 

[custard]

Interesting project.

The two sources I mainly use for dimensions are "Human Dimensions & Interior Space" by Panero and Zelnick, and "Designing Furniture" by Seth Stem.

They give lots of measurements for circular tables and for wheelchair furniture, but unfortunately neither specifically answers your question. However, one thing is detailed which could be relevant.

A wheelchair seems to take up a lot more space under a table (not only in height but also in depth) than a regular chair. The measurements given are 730mm under table depth clearance required by a wheelchair seated person who is sitting back, and 655mm for sitting forward. You could take measurements directly from your client but if that's the case it might be difficult to make a one metre diameter circular table with a central pillar accommodate a wheelchair at all, especially as the wheelchair occupant has less forward reach over the surface of the table so needs to get themselves close to the table edge.

A one meter diameter table would normally accommodate four people, but if you fitted it with three legs and a shallow apron then it could accommodate three people and have sufficient room underneath for a wheelchair, just a thought.

 

[custard]

I see Steve beat me to it with the three legged option!

 

[Zeddedhed]

Thanks guys for the swift response.

I fear I may not have been clear enough in my description.

The table needs to resemble this one....

Not necessarily in terms of detailing but in the way it's made - central column with three or four splayed feet.

Most of the ones I've seen never have the feet extending beyond the circumference of the top so I'm guessing my description led you up the garden path as it were. Apologies

 

[Steve Maskery]

Well if you want to make it with such a small footprint you need to make it have a very low centre of gravity. Maybe a hollow column filled halfway up with sand!

 

[Zeddedhed]

Well if you want to make it with such a small footprint you need to make it have a very low centre of gravity. Maybe a hollow column filled halfway up with sand!

Or I could bolt it to the floor!!

I feared this would be a tricky one.

I may try and convince the client to go for a tripod leg design instead.

By the way Steve, surely you should be out in the garden putting the finishing touches to your somewhat palatial workshop?

Is today a well deserved day off?

If so, enjoy and have a beer for me!!

 

[AndyT]

The stability of that design is going to depend on how weighty the top and base are, as well as their relative diameters. So you need to make the base as big as you can - which is not much, to get enough space underneath. The taper in the column helps maximise the weight at the bottom.

So as suggested, get plenty of weight in the base.

But there is also scope for keeping the top light. If you use MDF I would go no thicker than 18mm and I expect 12mm would be plenty but ply would be lighter still.
You can copy the one in your picture and make the top look more substantial by giving it a decent sized rim.

 

[Zeddedhed]

Thanks Andy, that all makes perfect sense.

Although it is yet to be discussed I am pretty certain the client will be against MDF or PLY. Solid wood is probably what he'll want (given his previous instructions on other projects) and will not be talked out of it.

I'm pretty certain that we'll be talking about a top mainly from Maple with a Walnut perimeter a Walnut 'ring' if you like. I thought that making this with a decent rebate inside and then dropping in the Maple (again rebated but in reverse). The He'll want a walnut string inlay about 60mm in from the edge of the walnut ring.

The base will probably end up being a circular column about 250 diameter from Maple with Walnut stringing around it's circumference at several places.

How do I know all this you ask?

He's a very predictable (but thoroughly pleasant and likeable) chap. He fully understands the work and subsequent cost involved in this sort of work and is very happy to pay for it.

I only hope I can do this one justice as it combines several things I've not really got much experience with.

 

[custard]

If you're looking for nice, unsteamed walnut then English Woodlands Timber has some good French walnut in stock in "AX" grade, their term for super prime! They're in Sussex so not a million miles from you. I've had a few boards from them recently and it's pretty good, if you're interested I can post some photos.

 

[Steve Maskery]

You could consider making the top as a torsion box, that would keep it very strong and very light.

 

[Zeddedhed]

You could consider making the top as a torsion box, that would keep it very strong and very light.

Thanks Steve. I've considered the Torsion box approach before for various table tops but I fear that on this project the client will insist on a solid wood top.

If I had any experience with applying veneers then I think I would try harder to convince him otherwise, but veneering is something I've never had a go at, and I don't fancy learning it on a paying commission.

 

[Sheffield Tony]

I would not go for 3 legs. The table overballances when the centre of gravity is tilted beyond the line between the two legs still on the ground. If the "radius" of tthe legs out from the centre of the table is r, the three legged table tips when the centre of gravity passes 1/2 * r. Four legs, 1/sqrt (2) * r, 6 legs sqrt (3)/2 * r. More legs the better, for the same radius. That's why office chairs often have 5 legs. Of course you have to weigh this against using fewer, but longer legs.

 

[deema]

I think I would look at having a polished or chromed steel base that's also round. This will least affect wheel chair access, provide good weight to hold the table stabile and also give a less 'chunky' look. I would also consider a steel / chrome pillar again to make the table look more modern and have cleaner lines. Three small feet under the disc at the bottom will ensure that any uneven surface is resolved. The disc could be any shape and laser cutting isn't that expensive.

 

[Phil Pascoe]

I don't understand the need to get a wheel chair under a table. I'd have thought the additional height would make eating at the table uncomfortable.

Written while sitting at a normal height table. In a wheelchair.

 

[Jacob]

The central pillar design of table in your picture is inherently unsuitable for a wheel chair user as there is too much clutter on the floor and at best you could only get your feet/chair halfway under it.
Better would be 3 or 4 legs with enough space between the legs to get the chair in.

 

[Phil Pascoe]

You couldn't get the chair half way under the table while sitting in it anyway. Three legs or four? Rather a moot point. The cross members on the floor might be a nuisance, but on balance probably not so much as a nuisance as legs at the corners which would be no disadvantage once seated but could restrict approachability.

 

[Steve Maskery]

My mate Dave and I have been discussing this and have come to the conclusion that 1m is a very small top under which to accommodate a wheelchair.
So, why not cut a 1m dia MDF top and screw some fake legs/column to it just enough to define the shape and size and see how it works in practice, before you build anything proper.

 

[Phil Pascoe]

If your dining chair was a "carver" you wouldn't expect to push the arms under the table while seated, would you? It's a few inches of the frame and front wheels at most that actually go under it. Steve's idea is good.

 

[Brentingby]

It seems a number of assumptions have been made about the user.

We haven't been told that wheelchair has arms. It may not have them. Even if it does, the user's knees may be high enough that they wouldn't be able to slide under a standard height table with a skirt as in the OP's photo.

We don't know if there is a foot rest, what kind it is or how much clearance there is above the floor if is used. That would have an effect on the design of the base. Will the users feet or the foot rest hit the column before the user is close enough to the table? Will the foot rest hit the feet? On a small table as in the OP's photo, it is likely that the foot rests, if used, would meet the feet of the table before the user gets close enough.

Much we don't know about the user or their wheelchair.

Assuming there is a footrest, a very low profile and heavy three or four-legged base would probably be best. Make it low enough so the foot rest can go over it. The base could be made of wood but filled with iron to increase the weight and lower the centre of gravity.