"The Outcaste" wrote in message
...
On Tue, 8 Jun 2004 10:47:31 -0400, "NetMax"
bubbled forth the following:

Personally, I think you could hold up many types of tanks by a wood
block
in each corner. The tank's base is held by the long sides, and the
amount of pressure needed to vertically break a pane of glass in a
vertical position should require many more times the amount of weight
in
the tank. The only concern is again, that the 4 corner blocks equally
contact the glass so no twist is introduced.
While I've done this with small tanks (5 and 10 gal), I'd be a bit
leery with anything much larger.

There's one website (can't find the link now) where they recommend
that the 4 sides of the aquarium extend below the bottom panel. This
is so you don't have to build a frame to hold the bottom panel up off
of a solid topped stand. In this case the bottom panel is only held by
the silicone, with not even the support of wood blocks under each
corner. However, I'm not so sure I'd want to put that much faith in
the strength of the silicone. The bottom joint will be under more
stress this way, not only the water pressure pushing the side panel
out, but the weight of the water and decorations pushing the bottom
panel down.

Most DIY sites show that the side panels should be resting on the
bottom panel. All manufactured glass tanks I've seen are built this
way. The forces on the bottom joint are mainly shear (water pressure
pushing the side panel out), with some compression from the weight of
the vertical panes. When you only support the 4 corners, you are
asking the silicone to hold the bottom pane up to the vertical panes,
which places the joint in both tension and shear, and silicone is
stronger under shear than tension IIRC. While it may hold for years,
you may be stressing the silicone to the breaking point. I have this
mental picture of very small earthquake, or just a 2 pound rock
slipping from your hand a few inches above the substrate being the
proverbial last straw. causing the joint to fail all at once, opening
up like a zipper, causing the bottom pane to break into many pieces.

Plus I'm sure this would void any warranty on the tank.

I have no scientific or experiential data to say it won't work, but
that mental picture makes me rather be safe than sorry, though as
always, ymmv

Jerry

What country are you in? From Europe & Asia, I tend to see more flat
bottom tanks (glass sides sit on bottom pane as you described), but the
bottom trim raises the bottom so it doesn't touch the stand. From North
American manufacturers, it mostly seems to be the opposite, where the
tank sits on the glass sides, with the bottom siliconed inside and above
the stand. I'm not familiar with the pros & cons, but it would surely
affect the jigging needed to build them. When I look at functional
design advantages and at manufacturing advantages, I see merit in both
designs, at least similar enough that there isn't an obvious better
design.

In case you are wondering where the edge bottom has a structural
advantage over the pane bottom, if we assume that the silcone bead
exceeds the worst case weight condtion in the edge bottom design, then
there is a superior bond between the bottom and the side panes with this
configuration. To explain in text is a bit labourous, but I'll do my
best. With a pane bottom design you mentioned, there are 2 silicone
beads. Bead 1 is between the glass surfaces and bead 2 is a chamfered
bead running inside the tank (on top). With the edge bottom design,
there are 3 silicone beads, between the glass surfaces, and a chamfered
bead on each side of the bottom pane. An argument could be made that the
strongest vector of concern is pushing outward on the side panes at the
very bottom, so 3 beads are slightly stronger than 2 (even if all 3 are
in line with the side vector, while the 2 bead design has 1 bead
perpendicular to the side vector).

If I sound like I know more than I do, then you are right ;~). I'm not a
mechanical engineer, but it's puzzled me how 2 different designs have
continued to co-exist. I don't think the average buyer notices one from
the other, so it would seem to be driven by internal forces rather than
consumers.
--
www.NetMax.tk