I’m going to embark on designing my own coffee table. But as I’ve been doing my rough sketches, I’ve started to wonder if there is a formula to figure out what is stable/safe vs. top heavy.
For example if I have a 40" round table, and I made the distance between the legs 6" obviously a slight tap of the foot would knock it over. Is there a formula I should depend on or should I build a scale model? Any help would be greatly appreciated.
Technically I’m sure it would be pretty easy to calculate the center of gravity and moment of force required to push it over from any point if you knew the weight of the materials. Standard physics textbook should give you the formula.
Better yet though I think that a rough judge based on similar tables and common sense should guide to a solution that is pretty close. After that you really just need to make a model or prototype and see…
not sure if this is exactly what you were looking for, but hope it helps. I believe that most people (esp. designers) have a pretty good inate feeling for stuff that like gravity and normal forces of nature if it’s something as simple as a table with legs (ie. not some crazy cantilevered, tensioned wire kinda thing).
Make some mockups to test it out, but I doubt you will be able to get the dynamic, top heavy look you want without a base. Essentially, by placing the legs so close together with such a large top, you are making in effect a single leg type of set up.
It’s a pretty simple calculation if you remember how to do free body diagrams from physics. If you know the mass and the center of gravity, you know the gravitational force acting on the table and where it’s applied. Knowing the height of the table and the distance from the edge to the leg gives you the moment acting to tip it over. When the latter force exceeds the former force, it tips. It’s best if you set all this up in a spreadsheet.
You need to decide on a reasonable force- I would say a coffee table should remain stable, at a minimum, with a 50 pound load applied to the edge. And probably I would use a higher force, like 100-200lbs. You really have to account for someone sitting on it. Anyway, once you’ve decided on a reasonable load, you just adjust all your variables until you get something that’s stable.
Scale models won’t help you much, and building a bunch of mockups takes time.
Thanks guys. I’ll dig into the old physics books then. I’m only planning on making one table, so you are right full scale mock-ups don’t make much sense. I’m just hoping to figure out as much as possible on paper before the blade hits the wood.
ironically, there is a “furniture” forum for questions like these.
a tip test is usually performed on many residential and office pieces.
some have specific testing requirements because of their applications.
mock ups will prove or disprove the safety of your design. something to consider about coffee tables in general is the casual nature of the environments they are often used. consider that sometimes people sit on them or that a toddler may pull themselves up onto it, for example.
This isn’t exactly planetary mechanics. It’s a 15 minute calculation (if you take your time). It would take me that long to change into work clothes and get my tools out. A cardboard or foam model isn’t going to have the mass of the real thing, so in this case it pretty much is a waste of time. You just determined that a foam coffee table tips over with 2 pounds of force- so how much force does it take to tip when it’s made out of 1/4" glass? All you’re going to learn is that pushing the legs or base further out decreases the tippyness, but you already knew that.
If this were a production piece, then making a reasonably accurate prototype would be a given. I’d still do the calculation first.
I remember a small nightclub in Chicago that had low tables that were incredibly easy to tip. I saw someone completely faceplant and wipeout all the drinks just because they leaned in to say hello to someone. It was pretty damn funny but definitely a huge design flaw.
The club is closed now. Obviously. Just thought I would throw that in.
At my previous employer, all tables had to pass a 50 lb. tip test, which involved placing 50 lbs of weight at the edge of the top in a location most likely to tip the table. Ideally, one wanted tables to be able to hold even more weight than that, but someone decided that 50 lbs was a good minimum (which still doesn’t allow for a child to try to climb on it, run into it, etc.).
At one time I worked on a formula for determining weather a table would tip or not before building it, but never could come up with anything that was consistent. The weight of the top plays a large role, the heavier the top the harder it will be to tip the table. Same for the base, provided it has a relatively large footprint and the weight is concentrated near the bottom. Best rule of thumb was to make the base footprint a minimum of 1/2 the size of the top. This is fine for coffee tables or other occasional items, but it can be problematic for dining tables depending on the design of the base.