Replies

1. 
   wdwerker | Jan 21, 2012 12:54am | #1

   good luck

    I recently finished a pair of bedside tables with a drawer that had thin legs and a full extension slide. I was shocked when the open drawer with a small cordless dril as a payload caused the whole thing to try to tip over.  I solved my problem by drilling 1/2 holes in the back apron and inserting 1/2 steel rods.  16- 2 ounce peices cured the balance problem.

   I will do a mock up before I get this far with mortice and tenons in solid mahogany.  Tables were designed to fit the available space but the size of the legs and framework and lack of a bottom shelf led to my problem. 33 years in the trade and I am still learning........

   Steve Duncan

   Fine Custom Woodwork  since 1978

   wwww.steveduncan.com

2. 
   bones | Jan 21, 2012 10:09am | #2

   There is a formula that beleive it or not is in nature.  It's often called the golden ratio or golden mean.   If you follow it, the proportions are pleasing to the eye.  It's why when you look at a piece it appears right to you. I've included a link that goes into great detail.   I triy to use it in gereral don't try to get the formula down to the decimal point when calculation your proportions just keep it in general close.   If you google golden ratio or golden mean you will find tons of info.   I did a quick search on golden ratio in furnitrure design and hit this one thats really detail but will give you the background.     Even if your not a math person, it will give you the idea .

   http://members.fortunecity.com/petemullard/mobaing.html

3. 
   RalphBarker | Jan 21, 2012 11:00am | #3

   Like Bones, I think the Golden Ratio can be applied to many things, including furniture design. I'm less clear, however, on how one goes about applying it to a design that either looks, or is, top-heavy. In that case, you might need to beef up the legs, or even add a visually (and, physically) balancing element to the lower section of the table. (The Golden Ration can be used to determine the location of that element.)

   Stability also depends on intended use. It may not be a good idea, for example, to build a five pound night stand if you plan to put a ten pound bible in the drawer.

4. 
   wdwerker | Jan 21, 2012 10:17pm | #4

   proportions

   If appearance is more the concern then if you have a 5 inch apron or drawer front on a 28 inch tall by 12 inch wide (front view) 

   I would put the shelf 19 1/2 inches below the apron, 12 x 1.618 =19.416   or you could use the distance between the legs x 1.618

   You can divide by 1.618 to get a pleasing relationship. Or you can use 1/3 or 2/3ds of a golden rectangle if the numbers do not come anywhere close to your desired  project size.

   The whole idea is if you use 1 x 1.618 ratio in several ways of your design the outcome is pleasing to the eye.

5. 
   purduedan | Jan 22, 2012 06:56pm | #5

   The golden ration has nothing to do with stability.  The center of mass and its relationship the the bottom of the legs are the important parameters.   Adding a shelf lowers the center of mass thereby making the table more stable.  That being said, I have made several end table of similar size to yours without shelves and have not had a stability problem.

6. 
   KWesenberg | Jan 22, 2012 06:58pm | #6

   Golden Ratio

   Like Bones stated, it's important. What hasn't been said that the rule applies to the height in relation to the width of the piece. The width versus the lenght. It's all important. If they are all correct, you will not have a piece that will fall over. Also use the guide lines of furniture standards. Good Luck with your piece.

7. 
   PSeverin | Jan 23, 2012 02:41pm | #7

   Belief in the irrational.

   There is no formula.  It depends on your tolerance for stability.  The response above that comes closest talked about center of mass.   What you've dimensioned seems tippy but as I thought about it a TV tray isn't far from the dimensions you gave and it is stable.   So it depends.  The physics of it is not contained in one irrational number.  The stance of a standing human is not 1 foot wide to 1.618 feet high.

    In tests there is an almost insignificant  preference for a rectangle that has a ratio based on the golden section.  Perhaps that is because our vision creates parallax and foreshortening and we have difficulty seeing the real ratios from most viewing positions.    But the use of a ratio in design does create repetition which people do find pleasing and is probably far more important than what the ratio is.  After all those gothic cathedrals are based on squares, double squares and the square root of 2,  another irrational number.   No wonder, you say, they called them gothic.

   There isn't one answer.  Many things work, can work well and are beautiful.

   Peter

8. 
   hammer1 | Jan 24, 2012 11:29pm | #8

   Most of the time, it's just good old common sense. If you think it's going to be top heavy, it probably is. A lower shelf will add weight towards the bottom of the table and that will help.

9. 
   swenson | Jan 26, 2012 11:11am | #9

   In a nutshell the problem is this.  You have a moving center of mass.  The drawer.  Once the center of mass moves outside the base the object will tip over.  A light empty drawer in a tall case has the center of mass below the drawer in thin air between the legs, when you pull the drawer out the center of mass raises up and forward but is still inside the base.  Loading the drawer with more weight moves the center of mass forward and up.  If the load is heavy enough when the drawer is opened the center of mass falls outside the base and the table tips. 

   The problem for the average woodworker designing a piece is it is hard to figure out where the center of mass is at any given time.  On that point I can't help.  There must be a formula.  Good luck.

   EDIT:  I just re read your post and realize I don't know if you even have a drawer and it was another post that had the weight tipping the table over.

10. 
    VAM | Jan 27, 2012 02:15pm | #10

    SketchUp?

    If you design in SketchUp, I think there is an add-on that lets you compute the center of gravity for a piece.  Maybe posting in the SketchUp section can get you information.

11. 
    acornw | Feb 11, 2012 03:41pm | #11

    PSeverin was most accurate in his reply.  There is no magic fornula for stability.

    Once upon a time, in the context of Period furniture, there was no carpet, few rugs, uneven floors and everybody, including older children, handled open flames every day.  Often these candles or lamps were set on three legged stands (for stabilty on the uneven floors) or tables. Lightweight and small, this primitive furnture was enough, adequate.

    Today, with the average household of 250 pounders, mocking up NFL plays and chase scenes would destroy such delicate items without a second thought.

    Context is everything.

    Dave S