Round Dining Table Tip Hazard

Re: Round Dining Table Tip Hazard

Barry Irby

I no longer have the mathematical skills to work out a proof, but I think you are correct. The tips of the legs need to be roughly the corners of a square that would just fit inside the diameter of the top.

Also, there are other factors, such as the weight of the legs and base and the geometry. If the legs are very heavy and very low it would be harder to tip the table because the center of gravity will be lower.

Incidentally, three legs are worse.

Re: Round Dining Table Tip Hazard

John K Jordan

Use more than 4 legs?

My 42" diameter table has the support points of the legs almost 10" from the edge at the maximum point. I tried leaning on the edge of the top with all my weight and it is very stable - it would take a couple of pretty massive kid climbing to tip it over. This is a heavy oak table with relatively massive legs and central column. The top is strong but relatively light in weight. With a center leaf to make a 42"x60" oval table the overhang is about 19" in the long dimension. It is also very difficult to tip in that direction.

I think you have to consider more than just the dimensions. I didn't get out the text books and run numbers but I think the mass distribution of the structure makes a difference. Consider the hypothetical and unrealistic case of a solid steel base and column weighing 2000 lbs with a very low center of gravity and a strong but light-weight top. Rather than do the math, perhaps mock up a cross section with 2x4 lumber. Make it with an adjustable center of gravity and use a spring scale to measure the force needed to tip for a given diameter, overhang and center of mass. That would give some feel for the variability.

BTW, you should be able to do a screen capture, paste that into an image or photo processing program, and save as a jpg.

JKJ

Re: Round Dining Table Tip Hazard

John K Jordan

I see that Barry posted similar thoughts while I was distracted.

Is this issue worth worrying about

Bill Tindall, E.Tn.

If one of my kids old enough to get onto the top of our dining table was found there the primary risk to their back side would not have been tippjng the table over. In the big picture of a kids exposure to life this risk seems too far down the list of concerns to worry about.

Re: Is this issue worth worrying about

John Jardin

I could not agree more...thanks for the common sense Bill

Re: Is this issue worth worrying about

Barry Irby

There is a risk here. Common sense is not common. If your grand parents failed to teach your parents to not climb on the furniture, your parents may not have thought to teach you. Snowflakes fall.

And there are some physics and geometry involved. Didn't you make a table with a petrified wood top? Suppose you had made it the classic three legged candle stand shape? That thing could take off a toe or worse.

So makers need to make things that have a reasonable chance of performing without hurting somebody. I bet you never considered attaching one of your chests of drawers to the wall. Your family knows better than to open the drawers in sequence and use them for stairs. Your chests are heavy enough to be stable. OTOH, Ikea sends a kit with every chest to attach it to the wall and prevent tipping. Their exposure is much greater than yours, the furniture is not as well made and the buyers are not as well trained, some lacking in common sense.

As makers we need to consider things like center of gravity. Very hard to tip over a pyramid. Broad base, low center of gravity. A table with a heavy top and a Krenov style base, not so much.

I have a floor model drill press. Nearly hurt me when it tipped over as I got as little too enthusiastic moving it. I still marvel at how top heavy it is and how small the base. The fall broke the table and I am really happy it was not my foot.

My kids saw me swat the cat off the table and learned the lesson.

Re: Is this issue worth worrying about

Buckaroo

Please let me explain about top heavy.

I also bought a top heavy floor model drill press decades ago!

BEFORE STANDING IT UP, COMMON SENSE made me realize, before it tipped over, to attach it to the wall so it couldn't tip/fall over.

That was decades ago & it still remains in the one & only spot/home it has ever occupied in my shop---chained to the wall!

WE ALL/EVERYONE, IS BLESSED WITH common sense.

What is important

Bill Tindall, E.Tn.

When people get up from a table they often push against the edge in front of the chair. It is this tipping that is important to deal with in design. Do you need to design to eliminate tipping from this force when the force is 300 pounds? Probably not for it will likely never be this much. How much. You have to decide.

The calculation is straightforward. The problem reduces to a teeter totter with unequal legs. What is the balance point. The leg needs to be equal or outside this point.

Kids (& Adults) - Common Sense?

Bill Howatt

Relying on common sense, training and education when dealing with kids and a lot of adults is a ridiculous premise. Sooner or later there is a chance somebody will intentionally or unintentionally do what they shouldn't. I've seen adults using folding rectangular tables as a "ladder" and then walk to the end and have the table tip.

If you are making something it should be inherently as safe as possible so the dumb things can't happen. Would you really feel good if your kid got seriously hurt if the table tipped even though he wasn't following your training orders? "Yes, little Charley is paralyzed but I warned him", isn't likely to go very far.

If your table is being sold then the risks multiply.

Bill

(Message Deleted by Poster)

one needs to go into the physics

Bill Tindall, E.Tn.

"So, without going into the physics, the table will be stable so long as the center of mass of the table is over the base.

This statement is true for a table at rest with no external force.

So, what you'll need to do is find the max load that you want to design for (i.e. the force of a person pushing down on it). Then find the center of 'mass' and make the base such that the center of ma i over the base."

This statement makes no sense. Again, the analysis is the same as for a teeter-totter. One arm of the T-T is the center of table mass times the distance this center of mass is from the leg (presuming the table will tip at a leg). The other arm is the force of this out of control kid times the distance his center of gravity is from the leg. The second result needs to be greater than the first to dump his butt on the floor along with dinner.

A mental calculation estimates that this kid is either way over weight or old enough to know better, or the table is made of balsa or it has a way out of proportion overhang to dump him on the floor. (girls would know better)

All the ladder back chairs need to be removed from this safe house as well as lamps on end tables. There was a day that most kids survived on the farm with potential hazards, if one's imagination ran wild, whose numbers vastly exceeded those found in a dining room. As you might tell I don't subscribe that a kid's environment should be made as safe as possible. Safe as possible involves too extreme measures and doesn't teach to avoid danger. Stitches and broken bones are part of healthy growing up. Permanent damage is to be avoided.

Re: one needs to go into the physics

rum

I had a response typed to explain this more clearly but just as clearly it's not desired. Never mind, sorry for attempting to contribute.