Choosing and Using an Automatic Lap

The first question you need to ask yourself is “how large are the pieces I want/need to lap?” Once you have your answer to this question you can begin figuring out what size unit will work for your application. Users tend to get the best results on a lap when the piece they are grinding is smaller than 1/2 the size of the pan and several pieces can be placed on the plate. Having multiple pieces on the pan ensures movement across the entire plate surface which also promotes more even plate wear.

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 a vibrating flat lap, 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.

It is best practice 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.


Besides size, what’s the difference between a Vibrating Lap and the Rociprolap? This is the single most common question we get from customers in the market for an automatic lapping unit. In a word, the answer is precision. The Rociprolap is a precision based unit where the vibrating lap is not.

Can the automatic Vibrating Lap grind my bottles? No. Any item that can topple over is not recommended for use on these units. These units are designed to work large flat pieces such as sheet or panel glass as well as book ends and stone slabs.

How fast will this unit lap my piece? If speed is what you are looking for, these types of units are probably not for you. It is difficult to calculate an exact time frame for lapping on these units because there are a variety of factors to consider. The biggest advantage to the automatic laps is that it takes the labor out of lapping. These units are designed for you to set in your piece and allow it to work while you work on something else.

Will the automatic laps polish my work piece? Yes. With the proper polishes and polishing pads, these units can be very effective at polishing. Remember, the key to getting a good polish is having the correct type of polish, the correct type of polishing pad, and a creamy consistency of polish and water on the pad.

Vibrating Laps

Covington’s Vibrating Laps are constructed of heavy duty solid cast aluminum. A counterweight is attached directly to the motor which creates the vibrating motion in the unit. The lapping plate is cast aluminum and features a cast finish. Any imperfections in the casting plate surface will be removed on your first grind. 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 only used for polishing.


Rociprolaps are constructed of heavy duty cast iron and are available in a variety of sizes including 20", 24", 30" and 36". These are precision based units. The bases are machined perfectly true and the bearing holes are held to very tight tolerances. The plate is machined perfectly flat and the bearing race on the back side is parallel and true to the plate. Little pockets are drilled into the face of the plate to promote a faster grind. Whereas the vibrating lap has a cast finish, the Rociprolap features a machined finish. Additionally, the vibrating lap only vibrates due to a counterweight attached directly to the motor.

By contrast, the Rociprolap requires a shaft with a perfectly engineered counterweight designed specifically to create the motion of the plate. The plate sits on nylon bearings which are designed to wear out so as to prevent damage to more expensive parts of the unit. The plate bearing fits the shaft neatly and the plate spins as it reciprocates creating one more dimension of movement than the vibrating lap. Please note that this unit is made of cast iron and it is impossible to prevent all rust. You can take precautions by cleaning out the plate after use and spraying the plate with WD-40.

Covington’s Rociprolap has only been modified slightly from the old Jack Rose design. We have changed the counterweight shape to be more efficient and added additional bearing cups to the base.