Lew Hodgett wrote:
Bill wrote:

This raises the question that has been kicking me around: Given a
base
with only 4 legs of support at the corners (say, like on the
Cedar-lined
chest you made for your daughter, only longer and wider),
wouldn't the frame be inclined to *sag* length-wise?
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Depends on the vertical height of the side and rear panels.

The larger the height value, the stiffer the box.

Some basic strength of materials.

I (Moment of Inertia) = (b*h^3)/12

Are you saying that *sag* is related to a rotational force?

Concerning "sag", it seem like we should be measuring the distribution
of mass between supports. If F=md is the force in the middle (of the
horizontal beam) and it is low, then we should experience less sagging,
right? The "trick" seems to be to make sure d is small. h appears to
have little to do with it. Not being an engineer, I only have a very
basic grasp of the concepts.

Please feel free to correct me, I like learning new things.

Cheers,
Bill





For a rectangle

Where b = base; h = height
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The larger the value of "I", the stiffer the beam will be.

The above is a very basic explanation.

For an in-depth explanation, construct a Strength of Materials
engineering text.

Lew