On my second week and third rev. of building my dirt/rock separator trommel machine. We didn't realize how much lava rock was back there until we tilled. Holy cow, I could open up a landscaping buisness with what's back there. 20' by 100' and probably 16" deep is mixed lava and dirt. The area where the garden will be is 12'x14' so at a foot down that's 6.2 cu. yds of sifting to do. Anyways, started sifting the dirt with just a screen and bucket and after an hour, I think I got 5 gal of rock and 5 gal of dirt. The "work smarter" creed settled in and I decided to build a better system. Current rev. is a screened frame attached to an outer frame with cabinet drawer sliders. I bolted a palm sander to the screen box to vibrate the piss out of it, and used bungees to give it some springage. Fired the prototype up last night and it looks like it will work, just need to mount it at about 20 deg. with some legs. Will post a review shortly.