Vibrating Table

I've been working on a vibrating table for the last couple of weeks (around holidays, family and campaign terrain), based on Ultrawerke's. I've wanted to do something like this for a while, and after seeing his, I realized I had pretty much all the parts he used. The only things I actually had to buy was the "shadowbox" frame I got on sale for $10 and a couple bucks worth of springs.



I grabbed a couple of old fan trays from work that were getting thrown out a while back. They came out of some pretty high end computer switches and were large (120 cm, I'm sure). I always thought I'd use them either for industrial terrain or to power a hover craft. ;-) Anyway, they're 12 volt, and I had a 12 volt wall wart laying around, so after grabbing a couple of bucks worth of loose dc power adapters from Radio Shack, I went to town.
The only thing is, Ultrawerke's computer fan is more manageable, because this fan spins like CRAAAAAZY. You'll notice that where he has a long bolt with a nut on it...I have a tiny washer. That's because when I glued a bolt to mine, it about vibrated apart throwing itself off the table. Even with just the washer, it still goes nuts and my molds slide everywhere-- hence the guard rails along the sides and the grip tape. I tried throwing a potentiometer in there to lower the voltage, but it seemed like it would only spin up at when the pot was turned to 0. I'm an electro-n3wb, so I'm not sure if I can lower the rpms. I guess I need to read up here and here, both of which seem to suggest that the pot method should have worked...may need to revisit that. Also, I shorted my first wall wart mocking this up with alligator clips, and my second one is putting out more like 15v... I might also look for some tighter springs.
I think the grip tape was actually useless or at worst counterproductive. I guess the movement isn't just side to side but also up and down, and the rough surface just doesn't help much. I think what I really need is a rubber surface for the molds to kind of stick to.
The little kickout to the side is where I'll mount the power plug and an on/off switch. The shadowbox frame is almost an inch thick, and it seems too much trouble to mess with. I'll just glue that on the side and drill a small hole to run the wires through.
I also probably need to go buy a piece of foam to sit this on so I can run it when the family is asleep. It gets a little loud and rattly.

Hirst Arts also has instructions for making a vibrating table.