Diamond Grinding Wheels Explained: Grit, Bond and Size

The Core of Cabbing: Diamond Wheels

If you are shaping cabochons or freeform lapidary pieces, diamond grinding wheels are your most vital and frequently used tools. Unlike traditional silicon carbide wheels that change shape as they wear down, diamond wheels maintain their precise diameter and flat surface, ensuring consistent results throughout their lifespan. The cutting action is achieved by microscopic industrial diamonds bonded to the surface of the wheel. To build or maintain a highly effective cabbing machine, you must understand the different types of bonds, grit sizes, and wheel configurations available.

Electroplated vs. Resin Bond vs. Sintered Wheels

The method used to attach the diamonds to the wheel determines how aggressively the wheel cuts, the finish it leaves, and how long it lasts.

Electroplated (Hard) Wheels: On electroplated wheels, a single layer of diamond particles is bonded to a steel core using a nickel plating process. Because the diamonds are exposed and rigidly held in place, these wheels cut very aggressively. They are the standard choice for the initial shaping stages, typically in coarse grits like 80 or 220. The downside is that once this single layer of diamonds wears off, the wheel is dead and must be replaced.

Resin Bond (Soft) Wheels: Resin wheels feature a thick layer of a durable resin composite matrix that is completely saturated with diamond powder throughout its depth. As the resin slowly wears away during use, fresh, sharp diamonds are continuously exposed. Resin wheels have a slight "give" or cushioning effect, making them ideal for the smoothing and pre-polishing stages. They are typically used in grits from 280 up to 50,000. These wheels leave a smoother finish than plated wheels of the same grit.

Sintered Wheels: Sintered wheels are the premium option for high-volume cutters. Like resin wheels, the diamonds are mixed throughout the cutting matrix, but instead of resin, they are embedded in a solid metal alloy bonded under intense heat and pressure. This creates a solid rim of diamond-impregnated metal, usually about 1/4 inch thick. Sintered wheels last significantly longer than electroplated wheels but require occasional "dressing" with an aluminum oxide stick to expose new diamonds.

Understanding Grit Sizes

Grit size refers to the size of the diamond particles. The lapidary process requires moving through a sequence of progressively finer grits to remove the scratches left by the previous wheel.

• Coarse (80 to 100 grit): Used on hard, electroplated wheels for rapid material removal and establishing the basic shape (the pre-form).
• Medium (220 grit): Used on an electroplated wheel to refine the shape and establish the dome of a cabochon.
• Fine (280 to 600 grit): This is the transition point, moving to resin bond wheels. A 280 grit resin wheel removes the deep scratches from the 220 hard wheel. A 600 grit resin wheel begins the smoothing process.
• Pre-Polish (1200 to 3000 grit): These fine resin wheels eliminate all visible scratches and begin to impart a dull shine to the stone.
• Polish (8000 to 50000 grit): These ultra-fine resin wheels create a high-gloss finish, particularly on harder stones like agate and jade.

Note that grits are often measured in "mesh" size for coarser wheels and "micron" size for ultra-fine wheels, though most lapidary suppliers convert everything to the standard mesh equivalent for simplicity.

Nova vs. Galaxy Style Wheels

When shopping for wheels, you will frequently encounter the terms "Nova" and "Galaxy," originally coined by Diamond Pacific but now used broadly to describe specific wheel styles.

Galaxy Wheels refer to aggressive, electroplated steel wheels with a textured, dot-like surface pattern. This pattern provides channels for water to clear away the rock slurry, preventing the wheel from clogging. They are used for the first shaping steps.

Nova Wheels are a specific type of resin bond wheel featuring a thick resin matrix over a semi-flexible foam backing, mounted on a hard plastic core. The slight sponginess allows the wheel to conform slightly to the curved dome of a cabochon, preventing flat spots and ensuring an even finish. They are the industry standard for smoothing and polishing.

Expanding Drums and Diamond Belts

An alternative to solid resin wheels is the expanding rubber drum. When the machine spins up, centrifugal force causes the rubber drum to expand, gripping a flexible diamond-impregnated belt slipped over it. The main advantage of an expanding drum is cost and flexibility. Rather than buying six different expensive resin wheels, you can buy one expanding drum and swap out relatively inexpensive diamond belts for each grit stage. The primary disadvantage is the time lost having to stop the machine and change belts between each step, compared to a 6-wheel cabbing machine where all grits are ready simultaneously.

Choosing the Right Diameter

Standard lapidary wheels come in 6-inch and 8-inch diameters. A 6-inch setup is standard and perfectly adequate for most cabochon making. An 8-inch setup provides a larger working surface and a shallower curvature, which makes cutting large cabochons and flat surfaces significantly easier. However, 8-inch wheels are substantially more expensive to replace.