Wednesday, September 19, 2012

The Vibrating Table

This is one of my favorites, and it never gets old…

First some background information -  One of the materials I will be working with extensively is concrete, in all its various forms.  Countertops, table tops, furniture, sculpture, all sorts of useful things that can be cast with concrete if you take the time to understand it.  The material is quite amazing.  It’s a proprietary mixture of cement, aggregate, sometimes other found objects like broken glass or molten aluminum etc., and very small strands of fiber to reinforce the mixture and cut down on the weight.  Challenge is, when you pour concrete into a mold, in order to perfect the cast, you need to have some way to get the air out. As it turns out, if you vibrate the whole thing at the right frequency, the air simply bubbles to the top and exits.  Hence the need for a really big, long table that floats on air and vibrates.

The initial layout of 4 inch square tubing
Heavy mounts for casters
Common sense tells us that concrete is heavy, so the first thing I did was design a really strong frame.  The specs for the table worked out such that it would hold over 4,000 lbs and be maneuverable around the studio.  Lots of steel, big casters.  Got that.

Final assembly of the frame
Once the frame was assembled I installed a pneumatic air lift system using some air bags originally designed for automobiles… think War’s (Why Can’t we Be Friends) circa 1975 “low-ride-er”.

Air bags for lifting the table top
Pneumatic controls and air bags
And a control system that would allow me to gently control how much “float” was in the table so I could better manage the frequency of the vibration (lower for lots of dry material, higher for wetter cement).

Add one 1,200 lb industrial vibrator
Add to this a powerful industrial vibrator like you would find in a factory or rail yard to help empty stuff out of big metal containers like rail cars.

The finished table
Voilà, a 9 ft table that lifts up, floats on air, and vibrates.

To test the table I went ahead and cast a counter top for one of the vanities in my loft (guest bedroom).  Here are some pictures of a small concrete top being cast in a 2-part mold.

The final mold assembly before the pour
The first part of the pour.  Notice the ripples from the vibration.
Adjusting the frequency to get the air out
Inserting the second half of the mold
The cast counter top, right out of the mold.  The hole in the middle is designed to accommodate a shallow reveal for a new vessel sink I have in mind.
Everything worked out perfectly.  When I’m not using it for concrete, I can use it as a mobile workbench.

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