I am planning to build a 42" x 60" dining room table that will extend to 84"
by adding 2 12" leaves. It will be a double-pedestal/trestle design. In
order to give it the recommended 16" legroom on each end, the trestle
assembly will be only 28" long (60 -(2x16)). That seems fine without the
leaves, but when the leaves are added, I then have a 28" overhang on each
end (12 + 16). In my sketch this looks quite unstable. I have seen tables of
this dimension on the internet, but don't know how they handle the stability
issue. It is quite possible that the combined weight of the trestle assembly
counterbalanced by the other end of the table makes this stable in use, but
how can I be sure, short of actually building it? It would be a serious
downer to build a beautiful table that capsizes if someone leans on one end.

John B wrote:
I am planning to build a 42" x 60" dining room table that will extend to
84" by adding 2 12" leaves. It will be a double-pedestal/trestle design.
In order to give it the recommended 16" legroom on each end, the trestle
assembly will be only 28" long (60 -(2x16)). That seems fine without the
leaves, but when the leaves are added, I then have a 28" overhang on
each end (12 + 16). In my sketch this looks quite unstable. I have seen
tables of this dimension on the internet, but don't know how they handle
the stability issue. It is quite possible that the combined weight of
the trestle assembly counterbalanced by the other end of the table makes
this stable in use, but how can I be sure, short of actually building
it? It would be a serious downer to build a beautiful table that
capsizes if someone leans on one end.

I would think that far too long an overhang, yes.

I would also presume the others have a folding leg or other arrangement
that extends further when the leaves are extended. One common
arrangement is a single leg which is hinged and mounted in the center
which would add half the width (roughly).

--

On Wed, 1 Apr 2009 16:46:19 -0500, "John B"
wrote:

I am planning to build a 42" x 60" dining room table that will extend to 84"
by adding 2 12" leaves. It will be a double-pedestal/trestle design. In
order to give it the recommended 16" legroom on each end, the trestle
assembly will be only 28" long (60 -(2x16)). That seems fine without the
leaves, but when the leaves are added, I then have a 28" overhang on each
end (12 + 16). In my sketch this looks quite unstable. I have seen tables of
this dimension on the internet, but don't know how they handle the stability
issue. It is quite possible that the combined weight of the trestle assembly
counterbalanced by the other end of the table makes this stable in use, but
how can I be sure, short of actually building it? It would be a serious
downer to build a beautiful table that capsizes if someone leans on one end.

This is a classic mechanical engineering statics problem. Find the
center of gravity and consider the total table assembly weight is at
this point. Calculate the moment arm (in foot pounds) and solve the
amount of force needed at the edge to tip the table. Or, you can
decide how much weight (downward force) you must apply to the edge for
the table to tip. If the legs are extend to the edge or beyond,
something will fail before the table tips. If too complex, provide a
pic link, and I'll solve it for you showing my work.

John B wrote:
I am planning to build a 42" x 60" dining room table that will extend to
84" by adding 2 12" leaves. It will be a double-pedestal/trestle design.
In order to give it the recommended 16" legroom on each end, the trestle
assembly will be only 28" long (60 -(2x16)). That seems fine without the
leaves, but when the leaves are added, I then have a 28" overhang on
each end (12 + 16). In my sketch this looks quite unstable. I have seen
tables of this dimension on the internet, but don't know how they handle
the stability issue. It is quite possible that the combined weight of
the trestle assembly counterbalanced by the other end of the table makes
this stable in use, but how can I be sure, short of actually building
it? It would be a serious downer to build a beautiful table that
capsizes if someone leans on one end.

You could eliminate the end seating in the 60" configuration and use these:

http://www.rockler.com/product.cfm?O...Select=Details

Then when the end leaves are inserted, you'd have seating on the ends.

On Apr 1, 6:29*pm, Phisherman wrote:
On Wed, 1 Apr 2009 16:46:19 -0500, "John B"
wrote:

I am planning to build a 42" x 60" dining room table that will extend to 84"
by adding 2 12" leaves. It will be a double-pedestal/trestle design. In
order to give it the recommended 16" legroom on each end, the trestle
assembly will be only 28" long (60 -(2x16)). That seems fine without the
leaves, but when the leaves are added, I then have a 28" overhang on each
end (12 + 16). In my sketch this looks quite unstable. I have seen tables of
this dimension on the internet, but don't know how they handle the stability
issue. It is quite possible that the combined weight of the trestle assembly
counterbalanced by the other end of the table makes this stable in use, but
how can I be sure, short of actually building it? *It would be a serious
downer to build a beautiful table that capsizes if someone leans on one end.

This is a classic mechanical engineering statics problem. * Find the
center of gravity and consider the total table assembly weight is at
this point. *Calculate the moment arm (in foot pounds) and solve the
amount of force needed at the edge to tip the table. *Or, you can
decide how much weight (downward force) you must apply to the edge for
the table to tip. *If the legs are extend to the edge or beyond,
something will fail before the table tips. *If too complex, provide a
pic link, and I'll solve it for you showing my work. *

What value should he use for a load that knocks over glasses and
spills soup, but doesn't cause the table to tip?

R

Phisherman wrote:
On Wed, 1 Apr 2009 16:46:19 -0500, "John B"
wrote:

I am planning to build a 42" x 60" dining room table that will extend to 84"
by adding 2 12" leaves. It will be a double-pedestal/trestle design. In
order to give it the recommended 16" legroom on each end, the trestle
assembly will be only 28" long (60 -(2x16)). That seems fine without the
leaves, but when the leaves are added, I then have a 28" overhang on each
end (12 + 16). In my sketch this looks quite unstable. I have seen tables of
this dimension on the internet, but don't know how they handle the stability
issue. It is quite possible that the combined weight of the trestle assembly
counterbalanced by the other end of the table makes this stable in use, but
how can I be sure, short of actually building it? It would be a serious
downer to build a beautiful table that capsizes if someone leans on one end.

This is a classic mechanical engineering statics problem. Find the
center of gravity and consider the total table assembly weight is at
this point. Calculate the moment arm (in foot pounds) and solve the
amount of force needed at the edge to tip the table. Or, you can
decide how much weight (downward force) you must apply to the edge for
the table to tip. If the legs are extend to the edge or beyond,
something will fail before the table tips. If too complex, provide a
pic link, and I'll solve it for you showing my work.

Wouldn't you only want to take the center of gravity of the table
assembly to the inside of the leg? The torque of the portion of the
table to the outside of the leg would be added to that caused by any
additional downward force on the table extension.

It would not be unreasonable for an adult to sit on the end of the
overhang, so the table top must be designed to be strong enough to
handle this.

Given that the trestle is 28" long (the same as the overhang itself),
the torque due to the portion of the tabletop over the trestle is
canceled out by the tabletop compromising the extension. The near leg
is the pivot point, so doesn't really factor into the equation (since
the moment arm is going to be small). To a first order, this means the
the sum of the torques due to the other extension and the other leg must
together be greater than the torque due to the person sitting on the end
of the table.

I suspect the table would have to weigh substantially more than the
person sitting on the end for it to _not_ tip.

Chris

On Wed, 1 Apr 2009 16:46:19 -0500, "John B"
wrote:

I am planning to build a 42" x 60" dining room table that will extend to 84"
by adding 2 12" leaves. It will be a double-pedestal/trestle design. In
order to give it the recommended 16" legroom on each end, the trestle
assembly will be only 28" long (60 -(2x16)). That seems fine without the
leaves, but when the leaves are added, I then have a 28" overhang on each
end (12 + 16). In my sketch this looks quite unstable.

We have a similar double pedestal table that was commercially
manufactured locally. The top measurement, with no leaves is 48x68.
The carved feet measure 53" length (toe to toe) and 27" width.
The legs come off at an angle from two octagon pedestals that are 34"
from the far side of one to the far side of the other.
Kinda like this....
\ /
O-----O
/ \

This has nowhere near 16" clear under the table end (or sides) to the
feet. But with the spead of the feet there is plenty of room for the
chairs. There is more overhang on the sides than the ends, I suppose
because they know you will use the leaves. This table can be extended
with 4-10" leaves.

If you figure the ratio to your top size it looks like about 46 3/4"
length and 22 1/2 " spread for the feet. You might want to check my
math...

I think something closer to these numbers might be more desirable. If
you don't angle the legs you might want to lengthen the distance
between the pedestals to make up some length.


Mike O.