3 versus 4 legged table stability

[Jason Morgan]

I am designing a poker table and going to go with a 6 sided design (primarily because I was recently given 6 chairs from my neighbor that will work well for the table). Anyway. I wanted to make a 6 sided pedestal base for the table, but that locks me into 3 or I guess 6 legs. An 8 sided pedestal would allow for the usual 4 legs, but I dont want to do an 8 sided base with a 6 sided table, nor do I want to do an 8 sided table (and be short two chairs).

I guess the heart of my question is, how much less stable is a 3 legged base of the same diameter as a 4 legged base. Also, what is the appropriate base diameter for a given table top diameter (for a 60" top, is a 24" diameter base okay or should it be larger?)

Thanks!

[Peter Quadarella]

I don't know the answer to you question, but what if you made the footprint of each leg bigger? The end of the leg could have two mini legs come out of it, like half of an oval or something like that. Something like this: ---{

[Brian Backner]

A three-legged base is always more stable than one with 4 or more legs.

Going back to Geometry 101, remember that any three points not on a line define a plane. Any four points not in the same plane define space. The point being that three legs will always be rock stable no matter their length or how uneven the floor on which they rest. To get a 4-legged table to sit solidly requires that they be the same length and be sitting on a very even floor. Think about how many times you've seen a 4-legged table with one leg shimmed to keep the table from rocking - have you ever seen a 3-legged stool or table treated similarly?

Brian

[Peter Quadarella]

Brian, in a sense you're right, but I think in this case we have to take into account how the furniture will be used rather than the stability of the table absent any outside forces (after all, making a table that will stand by itself, and doesn't have to worry about people eating at it, is the easiest thing to do).

The more likely scenario/worry is that weight is applied to a portion of the table top, causing it to tip. In this case the more support points the better off you are.

Picture a three legged table with a round top. You have 120 degrees of space with no support. Without going into to much detail, the worst case is someone puts weight directly between them, causing a force that pulls perpendicular to the legs. This force is proportional to the size of the angle between where you are pushing at where the leg is, in this case a max of 60 degrees.

With 4 legs, the max would be 45 degrees, and the force would be proportionally smaller. And so on if you had 8, 10, 87 legs.

For a triangular or square table this issue largely goes away, and the increased number of legs just helps with counterbalancing.

[Tom Esh]

A three-legged base is always more stable than one with 4 or more legs.Brian

Depends on what you consider "stable". For sure 3-legged won't rock or need to be shimmed, but it will tip easier. Sort of like those Frank Lloyd Wright 3-legged chairs - they don't rock, but you can sure fall out of one easily. :)

[scott spencer]

Depends on what you consider "stable". For sure 3-legged won't rock or need to be shimmed, but it will tip easier. Sort of like those Frank Lloyd Wright 3-legged chairs - they don't rock, but you can sure fall out of one easily. :)


My thoughts exactly....'cept for the FLW part (of which I know nothing)! :D

[Tom Esh]

My thoughts exactly....'cept for the FLW part (of which I know nothing)! :D


Not one of his more popular designs. There's one in the 3rd pic from the top here:
http://letterfromhere.blogspot.com/2007/06/frank-lloyd-wright-designer-of-tippy.html

[Peter Quadarella]

Also, a 3 legged table won't rock, but if it is off the table will be tilted instead :eek:

[Jason Morgan]

I think I am going to try 6 legs. One on each of the 6 faces. I think it will look kind of neat.

Anyone have a comment on base diameter to top diameter ratio? Any "golden rules" here?

[John Eaton]

The other issue you have is leg placement - I'd hate to be the person out of four that's straddling a leg all night...

-- John

[Jim Becker]

Three feet will always be more stable than four, especially when the floor is uneven. But you also have to design it so that there is a wide enough base to insure it will not tip.

[Tom Veatch]

Anyone have a comment on base diameter to top diameter ratio?

If possible without compromising the "tippiness" of the table, leave enough table top overhang so the table legs don't interfere with the legs of the people seated at your dinner party celebrating the new table. Unless of course you don't like guests and want them to go home early. ;)