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Carve a custom stone with your Flex Shaft, part 1

Get some diamond bits, get a plan, and get started. 
Carve a custom stone hero

To the uninitiated, the phrase “gem carving” could sound intimidating. But it’s not impossibly difficult or scary. If you have a plan mapped out, all you have to do is remove a little bit of stone at a time until your design is revealed. Simple, right? In fact, the trickiest part is not removing too much gem material at once. It’s easy enough, if you go slowly and think out each step as you work.

To make this project even better, the only major tool you’ll need is your flex shaft, equipped with some diamond-coated burs and sanding disks. Sure, you can cut your own stone with a lapidary trim saw and then grind that stone with a lapidary grinding machine. But if you don’t have those pieces of equipment, you can begin carving a cut piece of stone called a “preform,” or you could even carve a finished cabochon. Either way, the carving procedure is the same.

Follow these instructions to choose your stone, prepare it, and shape it for basic carving. Check out Carve a custom stone with your Flex Shaft, part 2 for the rest of the instructions on carving, refining, finishing and polishing your stone. 


  • A stone to carve, such as Andamooka rainbow matrix opal (choose from):
    • Rough gem material
    • Preform stone
    • Cabochon
  • Dust mask
  • Lapidary equipment (optional):
    • Trim saw
    • Flat lap machine, 400-grit diamond flat lap
  • Shape template (optional)
  • Water drip system (optional)
  • Flex shaft and/or handheld rotary tool
  • Diamond burs: various shapes and sizes
  • Wet/dry sandpaper and/or sanding disks: 200, 600, 900, 1200 grits
  • Magnifier
  • Clear lapidary sealant, such as Opticon



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Sketch your design.
Draw your carving design on graph paper (my design is a spider), incorporating a flat base into the design; when you’re setting the stone, the bezel or prongs will hold the base. Make sure that your base is an even thickness for easy setting. (PHOTO 1)

Be sure to make detailed top- and side-view sketches of your design. Keep in mind the stability of the design and the angles you’ll be able to achieve through carving. For best results, I suggest starting with a simple design that has few tight angles and areas that you’ll need to carve heavily concave from the side or underneath, called “undercuts.”

Select your rough rock. I selected Andamooka rainbow matrix opal for my carving. Make sure that your piece of rough is large enough to accommodate the largest dimensions of your carving. My rough is 35 x 25 x 7 mm (1 3⁄8 x 1 x 1⁄4 in.). Inspect your rough to select a piece free of any cracks or pits that might interfere with a clean carving.

If you’re starting with a cabochon instead of rough rock, skip to “Carving.”

SAFETY NOTE: It is important when you’re cutting and carving any stone to keep it wet at all times. Rock dust is harmful to your lungs and eyes; keeping your stone wet as you work and wearing a dust mask are the best precautionary measures.

Trim your rough. Using a fine-tip permanent marker, sketch the outline of your preform on your rough. I used an oval template [PHOTO 2]. Using a trim saw and leaving a 1 mm border, cut excess stone from outside the template outline [PHOTO 3].

Shape your rough into a preform. Using a wet 400-grit diamond flat lap , remove material [PHOTO 4] until you’ve worked down to the template lines. Do not bevel the sides of the stone; they need to be at 90° so you have enough material to carve.

Refine the base of the preform.
The base of your finished piece needs to be perfectly flat. Place your preform on a flat surface to check this. If it isn’t flat, grind the base with the flat lap.

Smooth the bottom edge of the base to remove any sharpness. A smooth edge will help prevent any cracks from occurring during the carving process or when you set the stone.



Andamooka rainbow matrix opal isn’t the only type of stone that you can use for this project. There are a number of other gem materials you could carve successfully. Look for stones that are hard and solid without any major inclusions or lines of cleavage. 

Here are some stones that are generally good for carving; we’ve included their rating on the Mohs Scale of Hardness: 

Agate: Mohs 7 Amethyst: Mohs 7

Chalcedony: Mohs 7 Citrine: Mohs 7

Onyx: Mohs 7 Quartz: Mohs 7

Tiger-eye: Mohs 7 Carnelian: Mohs 6–7

Jade: Mohs 6–7 Hematite: Mohs 5.5–6.5 

The tools and carving techniques you’ll use will depend on the stone you choose. Keep in mind that Andamooka rainbow matrix opal is a 5.5 on the Mohs Scale of Hardness. Because diamond is the hardest stone (a 10 on the Mohs scale), your diamond burs will work on any stone. But the sanding and polishing stages could require different techniques, depending on the hardness of your gem material. Consult a lapidary reference book, or ask your local lapidary club for their polishing recommendations.

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Transfer your design to your preform. Using a pencil or fine-tip permanent marker, draw your basic carving design on your preform [PHOTO 5]. Be sure to mark a line at the height you expect the bezel to reach on your base and also mark center crosshair guidelines that will help you keep your carving even.

Mark small circles to remind you which parts will be the highest points of the design. In my piece, these high points were the spider’s abdomen and the first joints of the legs. If these marks later rub off as you’re carving, be sure to redraw them, since they’re important reference points.

Lightly carve your design on your preform. You’ll want to refer to your sketches often as you carve to reorient yourself and ensure that you’re following your original blueprint.

NOTE: Keep your stone wet by working over a container of water, and either frequently dipping your stone in the water or setting up a simple lapidary system to slowly drip water on your stone as you work, like my gravity-fed system [PHOTO 6].

To give yourself guidelines while carving, use a pointed diamond bit in a flex shaft to trace over your design [PHOTO 7]. Redraw the high points, if necessary.

Define the low points. Using a cylindrical diamond bit, carve down to start defining the lowest point on your carving [PHOTO 8]. On mine, the combined head and body (called the “cephalothorax,” which is a bit front of center), is the major low area of the spider.

Judge the depth, keeping in mind the distance from this low point to the base. Don’t carve too much; leave enough material that you can carve a slope to the high points, like the transition from the cephalothorax up to the legs on my piece.

Establish the basic planes of the carving. Using diamond bits suited to the desired shapes, carve the basic shapes of the high and low points and the slopes between them, a little at a time, working to the same depth on all areas of the design to maintain proper proportions. Look at your stone frequently from all sides to monitor this.

As you work, be careful not to remove too much material. For example, when I began to create the slopes from the lowest points up to the highest points [PHOTO 9], I left enough material that I could round the cephalothorax later.

Refine the mid-depth points.
Once you’ve established the basic planes and the highest and lowest points of the carving, you can begin to shape the areas between them, called the “mid-depth points.” On my carving, the lowest point is the cephalothorax, so a good mid-depth point is halfway down the spider’s abdomen.  

Carve the basic shapes of the mid-depth points until you reach a spot when you need a smaller fine-tip diamond bit to continue. Remember to pay attention to your design’s high points and redraw guidelines and marks as necessary.

Find the rest of the instructions on carving, finishing and polishing your design in Carve a custom stone with your Flex Shaft, part 2.