Tippy ness ratio?

[andrew whicker]

I'm making a simple bar height laptop table for a record store. I'm using a metal base and a wood top.

She wants a ~20 inch deep top and 60 inch wide, 42 inch tall.

I'm thinking I'll put some sand in the base for weight. Anyway, this question has come up in my mind a few times: is there a rule for depth of top and height vs the base?

Maybe that's badly worded, but I'm wondering if there is a quick way to know if something will tip when leaned on.

[Mike Nolan]

I don't think there is a simple rule. Tipping depends on how hard something is hit and it's weight as well as it height to width ratio. I think you should consider where it is to be used and the effect of it tipping over. 40 inch high, 20 inch wide and a weighted bottom seems pretty safe.

[Wayne Lomman]

No hard and fast rules. There are many variables. Is it on carpet or hard floor? Is nit free standing or against a wall? Can you screw it to the floor? Since you are planning to counterweight it, and I think it's a good idea, put the sand in bags so you can add as many as you need but also remove them for ease of transport. Cheers

[Lee Schierer]

Weight and the location of the weight will be a major factor. Obviously more weight in the base will make it less likely to tip. A 24" wide base would be better than a 20" one. If the stand is to be on a bare smooth floor it is more likely to slide than tip. You would need some complex math to calculate the center of gravity and how much force it will take to shift the center of gravity beyond the edge of the base.

[Dave Richards]

Wayne's point about what the table is standing on is a good one. If it's standing on a flexible surface, it'll be less stable than on a hard surface.

If the table is on a hard surface, it wouldn't be difficult to determine the stability if you determine the center of gravity. You could also determine how much sand you need in a the base to improve the stability. You might not need any depending on the design. As long as the C of G stays within the base of the table, the table won't tip over. I made a simple table model (https://flic.kr/p/W9xbgF) and found its C of G. Then I rotated the model until the C of G was over the center of rotation. In this case it required tipping to about 33°. I used SketchUp for this but you could use whatever method you want. Doing it in SketchUp obviates the need for complex math.

[John K Jordan]

...you would need some complex math to calculate the center of gravity and how much force it will take to shift the center of gravity beyond the edge of the base.

I believe it would be easier to mock up the base (or more) and see how much angle is needed in the various directions to cause it to tip over. It doesn't take much extension of the base to make a big difference in stability.

In building a rocking horse I was concerned about tipping over backwards by an energetic kid. A bit of experimenting with some mockup runners suggested a design that has proven to be nearly un-tipable for three sons, two grandsons, and visitors. I did the same thing to design stability into a llama restraint chute I built from steel.

JKJ

[andrew whicker]

Thanks for all your responses! I'll see what I can do