SLABS TO CABS: How to Make Lapidary Cabochons
©2006-2015 Inland Lapidary
Creating beautiful, polished cabochons from slabbed rock is a rewarding process that (with a bit of practice) anyone can master. This guide will help you work through all of the steps required. You will need the user guides included with indicated machines for basic assembly and general operating instructions. We strongly suggest that you work through the process with practice pieces first. PLEASE, save that special slab for when you have a bit of experience with the machine. Remember to spend the necessary time at each step eliminating scratches before going on to the next step. There is no exact calculated time for each step, but with experience you will get a solid feel for what amount of grinding is necessary at each step of the process. No matter which step you are on, the following safety precautions and guidelines always apply:
Today there is a wide variety of pre-slabbed rocks available from which you can create beautiful cabochons. You want to:
Gemstones come in varying 'hardness' which will effect how you grind and polish them. In general, harder materials (like agates) take a nice polish easier than softer stones (like opal). Initially you will have more success and better results if you use harder stones such as Brazilian Agates. Knowing the hardness of the material you are working will help you obtain the best results in the sanding and polishing steps.
Machine Set-up: SwapTop™ Trim Saw following the instructions included with the unit.
If you’re going to use the cabochon in a commercial finding designed to hold a standard sized stone, it’s important to cut it accurately to a specific outline so it will fit. Templates are available to help layout specific sizes and shapes. Move the template around on your slab to find the most pleasing pattern for your finished cabochon. Take a permanent marker, aluminum or brass marking stylus and run it around the inner edge of the template as close to the edge as possible. You can also use the marker or stylus to layout a free form shape.
The next step is cutting the slab close to the desired outline on the trim saw. When you trim away excess material keep in mind that some of it could be used to create other cabochons or be used for inlay, intarsia beads or tumbled. So, as you cut away the excess material, do so in a manner that will maximize the rough remaining.
Always start the flow of the coolant before beginning your cuts. Coolant lubricates the diamond and keeps the working area of the blade clear of debris. You should not have water flooding the saw table. If a paste forms around the cutting area, increase the coolant flow; sawing dry will severely affect the life and performance of diamond blades. With practice you will soon develop a feel for the speed that does not slow the motor while giving you a good sawing rate. An alternative to this trim saw is to use a diamond band saw to rough shape the cabochon. Accurately cutting using a band saw can minimize the grinding step, allowing you to create more intricate shapes while conserving precious and expensive rough.
Take your time and carefully cut close to the outline using a series of eight or so cuts. Some stones will lend themselves to fewer cuts, and some will require more than just eight. All cuts should be made outside but close to your template line. Allow enough space, about 1/16" –1/8", for the material that will be removed in the grinding, sanding and polishing process. Careful cutting now will make successive steps easier and greatly enhance the appearance and quality of your final product.
After sawing, clean the cab and check your work. The next step in the process is to establish a smooth and accurate outline using the SwapTop grinder set-up to remove any margins or small corners of material left over from the sawing operation.
Machine Set-up: SwapTop Grinder / Shaper following the instructions included with the unit
Now you want to remove any margins or corners so that the cabbing “blank” is the shape and size desired. Place the cabochon flat on the grid surface. Turn the machine on and slowly move the material into the grinding head. Use a back and forth motion to remove material and shape the piece. Periodically check the stone’s size with the template or the mounting. It should be just slightly larger (1/32") to allow for material removed in the sanding and polishing processes. Do not grind until it slides through the template, or it will end up being too small.
Any time a paste forms around the grinding area, immediately stop and make sure adequate coolant is being supplied to the diamond drum. Grinding dry severely affects the life and performance of any diamond product. With some practice you will get a feel for the optimal grinding action and pressure. You may want to try this technique using a piece of scrap material first.
Finally you will want to establish a reference mark, or girdle line around the perimeter of the cab. This reference line marks the outermost edge of the cabochon, helps you judge the progress, and obtain more uniform material removal during the shaping process. Make the line using a permanent marker or aluminum pencil at about two thirds of the slab’s thickness and closest to the back side of the cab, leaving at minimum 1/16". The girdle height should be narrow enough to fit down into the finding and if it has a bezel you should be able to roll the bezel of the finding over it.
Machine Set-up: Dop pot with wax brought up to temperature following the instructions included with the unit.
Dopping is the process of securing the stone to a stick (dop stick) using a special (dop) lacquer wax. Doing this gives your cabochon a handle so you can more easily manipulate the stone on the flat lap machine. Dop sticks can be fashioned from a variety of materials; the most simple is a piece of wood dowel about 4-5 inches long..
Machine Set-up: SwapTop 8" or 6” Flat Lap Machine following the instructions included with the unit
To establish the basic cabochon shape you will begin with the 170 grit diamond lap. Refer to the instruction guide for mounting it to the master lap and installing it onto the machine. Spin to make sure that it is centered on the master lap.
The goal in cabbing is to produce a smooth and properly domed surface on the face of the cab while creating uniform wear on the diamond disc (to optimize its life). Use light to moderate pressure and inspect your progress frequently. You want to use a sweeping, J-shaped motion with the cab, pulling it towards you and turning the cabochon (about ¼ turn) as you go. Always keep the contact points moving on both the cab and the diamond disc. This is probably the most difficult part of cabbing to learn. There’s a certain feel when the motion and the pressure are correct. With a bit of practice you will learn that feel.
Always start the coolant drip and then turn on the machine. Any time white powdery residue appears on the lap it means that you are not using enough coolant and may risk damaging the diamond lap and/or your cab. Increase the coolant flow accordingly.
You can control how fast you grind by using the speed controller and the position of the cab on the lap. You will grind and sand more slowly near the center and more quickly as you move closer to the outer rim. Practice will help you determine the optimum speed and position for each step of the process.
Replace the 170 grit diamond lap with the 325 grit lap. Refer to the instruction guide for mounting it to the master lap and installing it onto the machine. Spin to make sure that it is centered on the master lap.
Use the same motion as before to continue to refine the shape; check the cabochon as you grind to be sure you are grinding symmetrically. You want to end up within a fraction of the girdle marking line. Frequently rinse and dry the stone to reveal the remaining scratches. When you no longer have any scratches from the 170 wheel and the surface appears uniform you are ready to move on to sanding. Thoroughly rinse the stone, dop stick and your hands.
Depending on the hardness of the rock and the desired finish you may wish, this may be a single or multi-step process. Practice, the type of material, and experience will determine just when your cabochon is ready for the final polishing step. When starting out we suggest you use both the 600 grit and 1200 grit laps included with your kit. You may find that some stones will be ready for polishing after the 600 grit step while others may require even finer grit laps or sanding media. These are available from Inland Lapidary as additional accessories.
Machine Set-up: SwapTop 8" or 6” Flat Lap Machine following the instructions included with the unit
This is where the hazy surface of your cabochon is polished to a high sheen. There are many different polishes, pads, and combinations of the two that can be used for a final polish. Those commonly used for stone include diamond compound (graded diamond particles mixed evenly in a water soluble carrier) or cerium oxide slurry and a felt polishing pad.
- Setting Up with Diamond Compound
Install this wet felt pad (or your preferred substrate) you’ve attached to the master lap onto your machine. Squeeze the syringe plunger to apply the diamond compound in a series of small dots (not balls or mounds, you just want pink ‘spots’!) around the pad surface; about a dozen on a 6"pad, and 16 or so on an 8" pad to start. Once charged you only need to apply additional diamond compound occasionally when you notice that the pad is no longer polishing.
- Setting up with Inland Polishing Compound (Cerium Oxide)
Install this wet felt pad (or your preferred substrate) you’ve attached to the master lap onto your machine. Make a slurry of the cerium oxide according to its directions. Apply a small amount to the pad; using a brush to paint radial lines that divide the pad into thirds or quarters (like a small pizza!) should be sufficient. A new felt pad may need additional cerium oxide applied until the pad becomes “charged”. Once charged you only need to apply addition cerium oxide occasionally when you notice that the pad is no longer polishing. Using excess cerium oxide can cause balls to form under the surface being polished and make scratches.
One of the most common complaints heard from beginners is that they never seem to be able to get the polish they want and that scratches seem to just appear when using finer laps and won’t go away. What is wrong?
This question arises quite often, and especially from people cutting FLATS into glass and stone. Flats are absolutely the most difficult things to cut and polish and that’s because the stone isn’t really being cut flat. Free-hand lowering and raising of stones makes for multiple facets even though it appears flat to the eye. Then, when you are really only polishing ONE of those “facets”, you think you are polishing the entire “flat”. Scratches remain in spots where the finer discs simply are not touching.
No matter what your cabochon shape, here are some trouble-shooting steps to help get the polish you want:
What you plan to do with your cab will help you decide if you are now done or whether you will need to finish the back side of your cabochon. It is recommended that you avoid leaving a sharp edge around the base of the stone as sharp edges chip more easily. It is a good idea to create a slight reverse bevel to the edge on the back side of the cab to help prevent such chipping. It also makes it easier to insert the cab into the finding as many have a small curve in the bottom. You can accomplish this using the Flat Lap machine or the Shaper / Grinder.
You may choose to polish the back of your cab. If the cab is being mounted and the back will not be seen you can opt not to finish the back side. However, if you want the back to have the same finished look as the front, then you will need to sand and polish the back side on the flat lap machine.
With some materials (like softer rocks) you will find that the polishing methods above do not offer a shine to your liking. The number of combinations of pads and grits used in polishing is almost endless. Some possible polishing compounds include standard cerium oxide (approximately 8,000 grit), diamond grit / powder from as “coarse” as 8,000 grit to as “fine” as 100,000 grit, tin oxide (approximately 14,000 grit), and other polishes like fine aluminum oxide, Linde A, etc. Alternate media, which will provide different results to the felt pads, include synthetic fibers, leather pads, cork, woods, ceramics, and even copper plates (into which diamond grit has been pressed).
One of the most exciting parts of this lapidary field is the opportunity to discover new rocks, techniques, and styles of presentation. We encourage you to join a lapidary club. Many of these clubs offer classes in lapidary. We encourage you to take as many of these classes as your time allows. Many of these clubs can further offer you the camaraderie and social network of folks who have been involved in this rewarding hobby for many, many years.
In some cases, you may find that your work requires alternate or additional steps to accomplish your desired results. Inland offers diamond flat laps in additional grit sizes. In some cases, you may find that your work requires alternate or additional steps to accomplish your desired results.
Inland Lapidary also offers more than 300diamond grinding wheels and drums, diamond saw blades, diamond laps, and other diamond tools for use on our own and other manufacturers’ lapidary machines. You will find replacement diamond grinding wheels and diamond flat laps for cabbing machines by Diamond Pacific, Graves, and more. Our sintered diamond laps perform beautifully on faceting machines by Ultra Tec, Fac-ette, Graves, Polymetric, Facetron, and OMNIe, as well as legacy faceting machines like Sapphire and Raytech-Shaw.
We are proud to offer these and other lapidary supplies includingdiamond grinding heads, bits for wire wrapping, Electroplated and brazed diamond core drills, dressing sticks, diamond drill bits, and carbide wheel cutters, for both professional rock cutters and gem makers as well as casual rock and mineral hobbyists / collectors.
We manufacturer the best-sellingDB-100™ Diamond Band Saw and the SwapTop™ system of lapidary machines which include an 8" & 6" Flat Lap Machines, a Diamond Trim Saw, and Drum Edge Grinder. The SwapTop System allows you to configure one motor and base into 1, 2, or 3 different machines that can be purchased separately or all together in our exclusive All-In-Wonder™ Complete Lapidary Workshop.
We are regularly enhancing and expanding our line of products we manufacture (the most recent being the DopStation™ and large selection of professional gradesintered carving burs are now available in four different grit sizes), and the lines of products we handle from other manufacturers (we are currently authorized dealers for 3M Microfinishing pads, Graves Faceting, Diamond Pacific, and Estwing).
Please visitinlandlapidary.com for our complete line as well as a comprehensive resource library of lapidary links including other How To guides like this How to Cab (also available as a PDF
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