Vibrating Table

I was recently contacted about the design of my vibrating table with some ideas about possible improvements. I thought it would make sense to move that conversation here, to benefit the community and possibly get more ideas.

My vibrating table, shown below, is built using Anthony Lange's table as a model. Anthony posted about his design in the ' Building a vibrating table ' discussion.

The blue things on the top are bumpers made of Sugru.

Here's the message I received:

I saw you and Anthony from The Chocolate Life forum fixed the compression spring, under the table and locked the top with two bolts. But the vibrating source push up to vibrate, so I was wondering if fixing two springs on the bottom and top of the table and adjusting the pressure on the vibrating source would give more freedom for the table to vibrate.

I replied with the following:

My vibrating table works ok, but is definitely not ideal. It's on my list of projects to redo or at least improve. The design makes it so the vibration is strongest in the center over the vibrator and weaker-to-nonexistant at the corners. I think this is due to the placement of the springs and the use of plexiglass which is too flexible.
As you note, the spring placement doesn't really make much sense. It would make a lot more sense to have the springs on top (using longer bolts), allowing the table top to vibrate up from the vibrator. As it is, the table top is restricted by the nuts. i don't think the springs on the bottom are or would be necessary at all.

Even with moving the springs above the table top, the flexibility of the plexiglass will allow for vibration variation at different places. I think it would be better than the current design, but a rigid surface would work much better.

I'm planning to move the springs to the top and either reinforce the table top with metal bars, or replace it with a metal plate or something.

Has anyone else built a vibrating table using a similar design, or one that works better? Have you made any (or have any ideas for) improvements? I'd love to hear them, if so.

-Ben