In rock and gem cutting, you need something to... well, cut ‒ your material. And while you can use other methods to break your rough rock (e.g., rock hammering, throwing it to shatter into smaller pieces, etc.), cutting it precisely with a saw is the best method, both for precious and semi-precious rock. It reduces the "waste" that you get when shattering the rough. When cutting rock, especially the more valuable ones, we don't want to waste any of the material if we can help it.
Diamond blades are the blades used in lapidary saws. They are preferred to regular saw blades because they are designed to cut denser and harder materials. Diamond saw blades have diamonds evenly embedded into a metal matrix that makes up the rim, which cuts directly through the material.
If you're wondering whether "diamond blades" have real diamonds, the answer is no. The diamonds used in these blades are synthetic diamonds, also known as lab-grown diamonds. They are created by scientists in a laboratory by growing a small diamond seed in layers through high pressure and temperature.
Although these diamonds are synthetic, their physical and chemical properties are the same as natural diamonds. Thus, their hardness is no different and they can still cut through most hard materials.
Types of Diamond Blades
In lapidary, there are three common types of diamond blades. Those are sintered rim, segmented rim, and notched rim blades.
A sintered diamond blade is a continuous rim blade, where diamonds are embedded in the metal alloy. If ever the metal bond wears out, new diamonds will be exposed and the blade will continue cutting. This is a thin blade and is perfect for cutting precious gemstones and soft materials, because of it having less kerf and the clean-cut it gives.
Segmented rim blade has wide and deep gullets to allow the coolant to flush the dust and cool the blade. This is a versatile blade. It can cut precious and semi-precious rock precisely.
Notched rim blades are a production blade that can withstand demanding usage. It has small notches where segments are inserted and pressed to form the rim. This has the longest life, hence it is popular in industrial lapidary.
Wet or dry cutting?
In certain instances, like using other kinds of diamond blades in construction, or when cutting softer materials like asphalt or cement, a diamond blade may cut dry.
However, it is not the case when it comes to cutting rock and gemstones. In lapidary, a saw and a diamond blade can only be used in wet cutting. This is crucial in preventing friction or heating up between the blade and the rock. It will also make the blades last longer.
How do diamond blades work?
Although we say "cutting rock", diamond blades don't actually cut, they grind! The diamonds are supported by the metal matrix, and the exposed bits of diamonds grind a kerf onto the material. A kerf is the width of the material that is removed in grinding.
If the diamond blade keeps on grinding and is used for a long time, the diamond and metal bond will slowly wear out, exposing new diamond bits. This cycle will go on until no diamond is left on the rim. When the diamond is consumed and the blade won't grind anymore, that's the time when you have to replace your blade.
Sizes and Quality of the Diamond
When choosing a diamond blade for rock cutting, you need to consider the size and quality of the diamond. For sizes, the higher the number, the finer the diamond particles and the smaller the number, the coarser the blade will be. If you're cutting hard materials, it's best to use a blade with fine diamond, while coarse particles are used when cutting a softer material.
A good quality diamond is determined by its ability to withstand high temperatures and maintain a sharp point. Some diamond blades in the market are sold really cheap. Those kinds of diamond blades have poor quality and will wear out after only a few uses.
Diamond Blade Maintenance
Aside from using an appropriate high-quality coolant, a diamond blade needs to be sharpened every once in a while to maintain its performance. If your blade stops cutting or isn't producing good cuts, it probably needs resharpening. In most diamond blades, as long as the metal alloy and diamond are present on the rim, a blade can be salvaged by resharpening.
There are various methods of sharpening a blade, as recommended by other lapidarists. Those are cutting through obsidian rock and silicon carbide block. They're both acceptable methods, but the results aren't remarkable.
John Rowland, CEO of Highland Park Lapidary, made a video on how to sharpen a diamond blade, using a bastard file. In his tutorial video, he demonstrated how to pound lightly onto the rim of the blade, to expose the diamonds.
Watch the video here: