Above is a flat-lap machine I constructed using a Makita grinder mounted inside an old kitchen cabinet. The diamond lapping disk (China) is mounted inside an oil-drain pan (O'Reily Auto Supply) and attached to a 12" threaded shaft extension (Home Depot) added to the grinder. Speed control is by a router speed controller (Harbor Freight) mounted on the framework at the right above. Lubrication is fed through a tube from a plastic lemonade bottle (Wal*Mart) hung above; overflow drains into a 5 gal. bucket.
Here is a link to a YouTube video showing and discussing this home grown flat lapidary machine. http://youtu.be/rtL0vDIagJc
At left are my tumblers, located in the garage because the constant noise was unpleasant to listen to in my shop. (Also, there is not that much room) Two bench-top units are mounted on the cabinet to the left. I also purchased a tread-mill on Craig's List and can polish large rocks (and large quantities of rocks) in plastic barrels that turn in the framework I constructed with the walking surface of the treadmill propped at an angle. http://youtu.be/6P9xfO0WYv8
Below left is a vibrating flat-lap polisher used to put a high polish on cut stones. Below is the view into the polishing tray - I used hole-saws as weights on the thinner stones. The vibrating of the tray continually rubs the bottom of the stones with the same grit used in the rotary tumblers. http://youtu.be/X7LG5j641kw