Bags of sand instead of cement in table?
On: Fri, Aug 03, 01 01:40:02 PM
Michael S wrote:
|I was just wondering if anyone has tried bagging up sand in
thick bags possibly innertubes for an isolation table. The
bags of sand would replace concrete tiles or slabs making
the table cheaper. Or is concrete used for its stability
not just weight? Let me know if you think this might work.
Thanks in advance.|
Brian - Fri, Aug 03, 01 02:15:34 PM There's 2 things to consider:
1) your isolation table needs to dampen external
2) your isolation table needs to dampen internal
I'm currently building an isolation table, but I'm using
both steel and sand, plus inner tubes. The steel sits
on top of the sand (2" thick at 5' x 3') The sand and inner
tubes will damped any external vibrations from the floor,
but the steel will dampen or at least keep steady all
vibrations generated on the table itself. If the steel plate
moves, all of the components will move with it and thus
you're okay. Using just sand is fine, but you have to let
all of your components settle in the sand for quite some
time. By using steel, you don't have to worry about that.
Michael S - Fri, Aug 03, 01 07:21:54 PM I plan on using the sand as weight on top of a large
innertube but below a 4'x4'x1/4" piece of steel. I was told
that the 1/4" plate would not provide enough weight by
itself. I figured it might be a cheaper alternative to
concret blocks. My setup is on a concret floor in my garage. 188.8.131.52
Brian - Fri, Aug 03, 01 09:30:59 PM Michael, that's pretty much exactly what I'm doing too. I
did some pretty lengthy calculations to get the weight
correct. My 3'x5' steel top weighs 150lbs. To cover the
table top with 2" of sand will require250lbs of sand.
That plus lumber is roughly 500lbs. My 8" rim inner
tubes can comfortably hold 140lbs before they get too
"stiff" from over pressure, so 500lbs / 4 = 125lbs which
is will within range for the inner tubes to still function.
Colin - Sat, Aug 04, 01 10:12:17 AM Stiffness is a very important criterion as well. Holography
benches are often built on a 12" thick granite block
because it is very stiff. It is actually easier to isolate
a light stiff table from external vibrations than a heavy
stiff table because of the natural resonant frequencies
I have a 3'x5'x1/2" steel plate that is very well isolated
above 15hz and very well damped below 15hz. It is resting
on cinder block on my concrete floor in the garage. With an
interferometer I can measure the flex in my table from
changing my weight from foot to the other! I have to stay
very still during my exposures.
I am redesigning my table after a long conversation with
Jonathan H. After some research I decided a reasonable
stiffness would be a deflection of .00006 mm with the
addition of .5 Kg of mass.
Since I don't have a lot of money and need to move my table
someday I am designing a composite structure. Take a look
This is my design ideal. I can't manufacture a honeycomb
core So I am looking into alternative cores. 184.108.40.206
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