Using an Automatic Lap
The vibrating laps work by putting loose grit directly into the pan, adding water, and placing in your piece. The green pad that comes with the unit is designed only for use when polishing.
Small slabs and light pieces will need to be back weighted so that the piece grinds rather than hydroplanes on the water. A back weight can be as simple as a lead fishing weight added to the back of the piece and stuck in place with a little dop wax. This process discourages hydroplaning and promotes a more effective grind. Back weights will be necessary for all thin slabs and may even be necessary for bigger pieces.
Automatic laps are NOT designed for lapping anything that could potentially topple over onto an unintended side. Examples of such items include glass bottles or vases and other unevenly weighted objects.
The Rociprolap® and the Vibrating Laps work similarly. Both require putting loose grit directly in the pan, adding water, and placing in your work piece(s).
When using these units, it is important to listen to the piece while it works. If you hear a continuous scratching noise, your piece is grinding effectively.
Do not put in too much water because the piece will hydroplane across the water and not actually grind. Likewise, if you have too dry of a mixture, you will not get an effective grind. You are looking for a creamy consistency in both your grinding and polishing stages.
Best Practices: It is best to put in your piece and work on something else nearby so you can make sure the unit is grinding effectively all day. Add water and grit as necessary to maintain an effective grind.
Cover the face of your work piece with black sharpie marker. Place the piece marker-face down onto the unit and allow it to grind. Once all the sharpie marker is gone from the face of the piece, you are ready to move on to the next step.