Lapidary Saw Blade Sizes and Uses: Arbor, Kerf, and Diameter Explained
Here's the thing nobody tells you about lapidary saw blades: that number on the box—6", 10", 14"—tells you almost nothing about whether it'll actually fit your saw.
Walk into any lapidary supply shop and the blades are organized by diameter. The product listings online lead with diameter. The box has the diameter in large text. Meanwhile, arbor size gets printed in 8-point font on the blade itself, usually somewhere you can't read without good lighting and reading glasses.
The problem is that "10-inch blade" is describing the blade's diameter, which is only one of three measurements that matter. The other two—arbor size and kerf width—determine whether that blade will physically mount to your saw and whether it'll cut the way you expect. And unlike the diameter, these numbers are usually printed in tiny text on the blade itself, not on the box.
Arbor size is the diameter of the hole in the center of the blade. Lapidary saws use 1/2", 5/8", or 1" arbors depending on the saw's design. If your saw has a 5/8" arbor and you buy a blade with a 1/2" hole, you now own an expensive metal frisbee. Blade bushings exist to adapt blades—5/8" arbors can be bushed down to 1/2", and 1" arbors can be bushed to 3/4" or 5/8".
Kerf width is how much material the blade removes as it cuts. Standard lapidary blades typically have kerfs around 0.044" to 0.130" wide depending on whether they're designed for trimming or heavy slabbing. That sounds tiny until you're slicing a $40 piece of gem rough and realize each cut is removing a noticeable amount of material you could've used. Ultra-thin kerf blades exist with thicknesses as low as 0.1mm (about 0.004"), specifically designed for cutting expensive stones like turquoise and opal where material waste needs to be minimized. These thin blades are also more fragile and require careful handling.
The diameter determines what you can physically fit in the saw's cutting chamber and how deep you can cut. Trim saws with 4" to 8" blades are designed for cutting smaller stones, typically less than 2 inches thick, while slab saws with 10" to 36" blades handle large rough rocks. As a general rule, circular saw capacity is about one-third of the blade's diameter. The listing that says "cuts up to 3 inches" is assuming you're cutting perfectly flat slabs, not lumpy nodules of agate that need to clear the blade guard.
What makes this especially confusing is that lapidary saws and tile saws use completely different blade systems despite looking similar. A tile saw blade has a different arbor size, different kerf characteristics, and a much more aggressive cutting pattern designed for ceramic, not stone. They're not interchangeable, though people try anyway and then wonder why their jasper comes out looking rough.
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Understanding Arbor Sizes in Lapidary Blades
The arbor is the shaft that the blade mounts onto, and the arbor hole is the corresponding hole in the center of the blade. These two measurements need to match exactly. Lapidary saws typically use three standard arbor sizes: 1/2", 5/8", and 1".
Most blades come with a 5/8" arbor hole and include a bushing that allows them to fit on 1/2" arbors. Larger saws, particularly those designed for industrial use or heavy slabbing, use 1" arbors. Some blade manufacturers offer blades with both standard arbor holes and metric equivalents—5/8" converts to approximately 15.875mm, which appears on some European-manufactured equipment.
| Arbor Size | Metric Equivalent | Typical Saw Type | Bushing Compatibility |
|---|---|---|---|
| 1/2" | 12.7mm | Small trim saws | Can be bushed from 5/8" |
| 5/8" | 15.875mm | Most lapidary saws | Can be bushed from 1" |
| 1" | 25.4mm | Large slab saws, industrial | Can be bushed to 3/4" or 5/8" |
The arbor size isn't arbitrary. It corresponds to the torque requirements of the saw. Larger, more powerful saws that cut through thick slabs of hard material need the structural support of a larger arbor. Smaller trim saws designed for precise cuts on smaller stones can use narrower arbors. When you see a blade listed with multiple arbor options—for example, "1/2" & 5/8" arbor"—that means it comes with a removable bushing.
Blade bushings are simple metal rings that fit into the arbor hole to reduce its effective diameter. They're cheap, easy to install, and solve the compatibility problem in one direction: you can always make a larger hole fit a smaller arbor with a bushing. You cannot, however, make a smaller hole fit a larger arbor. There's no practical way to enlarge an arbor hole in a diamond blade without specialized equipment, and attempting it will likely ruin the blade's balance.
This is why checking your saw's arbor size before ordering blades matters. The information is usually in the saw's manual or stamped somewhere on the saw's housing near the blade guard. If you're working with a lapidary saw that's been around for decades, the arbor size might not match current standards—older saws sometimes used non-standard measurements.
Kerf Width and Material Loss
Kerf width is the thickness of the cut the blade makes, which equals the thickness of the blade at its widest point. In lapidary work, where you're often cutting expensive or rare materials, kerf width directly translates to how much material you're turning into dust with each cut.
Standard lapidary blades used for general slabbing have kerfs ranging from about 0.044" (roughly 1.1mm) for notched rim blades designed for production work, up to 0.130" (about 3.3mm) for thick sintered blades built for cutting large, hard materials like agates and geodes. The thicker blade provides more stability and durability during heavy cutting, but removes more material in the process.
Ultra-thin blades designed for trimming valuable materials have kerfs as narrow as 0.1mm (0.004"). These are popular for cutting materials like opal, turquoise, and other soft or expensive stones where every fraction of a millimeter matters. The tradeoff is that these thin blades are more fragile. They require careful handling, properly aligned equipment, and steady pressure during cutting. A thin blade on a poorly maintained saw with a warped arbor or loose mounting will wobble, potentially ruining both the cut and the blade.
When manufacturers advertise blade thickness, they're usually referring to the core thickness of the blade body, not the kerf width. The kerf width is determined by the diamond-embedded rim that extends slightly beyond the blade core. This is why you'll see specifications listing both "blade thickness" and "kerf width" as separate measurements.
The practical impact of kerf width becomes obvious when you're cutting expensive material. If you're slicing a piece of gem rough into multiple slabs, each cut removes material equal to the kerf width. Cut a stone into five slabs with a 0.090" kerf blade, and you've lost nearly half an inch of material across those four cuts. Switch to an ultra-thin 0.1mm blade, and you lose only about 0.016" total—saving roughly 0.4" of usable stone.
| Blade Type | Kerf Width | Material Lost (4 cuts) | Best For |
|---|---|---|---|
| Ultra-thin | 0.004" (0.1mm) | 0.016" | Opal, turquoise, expensive stones |
| Sintered (thin) | 0.060" | 0.240" | General lapidary, mixed materials |
| Standard notched | 0.090" | 0.360" | Production cutting, common stones |
| Thick sintered | 0.130" | 0.520" | Heavy slabbing, agates, geodes |
Thicker kerfs aren't inherently worse. They provide stability, longer blade life, and more consistent cuts on large, hard materials. The thick sintered blades used in industrial lapidary work can handle the stress of cutting large geodes and slabs of jasper hour after hour. They track straight through the material without deflection. For production work where you're cutting common materials in volume, the material loss from a thicker kerf is less important than the blade's durability and cutting speed.
Blade Diameter and Cutting Capacity
Blade diameter is the measurement from one edge of the blade to the opposite edge, passing through the center. It's the number prominently displayed on packaging and product listings. But what it actually tells you is the maximum cutting depth of your saw, and this relationship isn't straightforward.
For circular saws in general, cutting capacity is approximately one-third of the blade diameter. A 6-inch blade can typically cut about 2 inches deep. A 10-inch blade gets you roughly 3.5 inches. An 18-inch blade can cut close to 6 inches. The exact capacity depends on the saw's design, particularly the height of the blade guard and the position of the work surface relative to the blade.
| Blade Diameter | Approximate Cutting Depth | Typical Application |
|---|---|---|
| 4" | ~1.3" | Small trim saw, jewelry work |
| 6" | ~2" | Standard trim saw |
| 8" | ~2.7" | Large trim saw |
| 10" | ~3.5" | Small slab saw |
| 14" | ~4.7" | Medium slab saw |
| 18" | ~6" | Large slab saw |
| 24" | ~8" | Industrial slab saw |
Lapidary saws are typically categorized by the blade diameter they use. Trim saws use blades between 4" and 8" in diameter and are designed for cutting smaller stones, usually less than 2 inches thick. These saws are compact, relatively affordable, and ideal for precision work like cabbing or preparing small pieces for jewelry making.
Slab saws use larger blades ranging from 10" up to 36" or even larger for industrial applications. A 10-inch slab saw can handle rocks roughly 3 to 4 inches in diameter. An 18-inch saw can process significantly larger rough material, cutting slabs from rocks the size of a basketball. The largest saws, used in commercial operations, can slice through enormous pieces of material for decorative stone applications.
The cutting capacity specification in product listings usually assumes ideal conditions—a flat surface on both the material and the work table, with the material positioned to maximize the available cutting depth. In practice, irregular stones, safety guards, and blade guards reduce the effective cutting capacity. A lumpy agate nodule with a 4-inch diameter might not fit under the blade guard of a saw rated for "4-inch cutting capacity" because the clearance is measured at a specific point, not across the entire cutting area.
Blade diameter also affects cutting speed and blade life. A larger blade has a greater circumference, meaning each rotation covers more distance. At the same RPM, a larger blade's edge moves faster, which can result in quicker cuts. Additionally, the diamond rim on a larger blade wears more slowly relative to the number of cuts made because the wear is distributed over a larger surface area.
The relationship between blade size and saw power matters. Larger blades require more powerful motors to maintain cutting speed. A 10-inch blade on an underpowered saw will bog down and grind rather than cut. The saw's motor specifications should match the blade size—typically, larger saws have motors rated at 1/2 HP or more for continuous operation.
Blade Types and Their Kerf Characteristics
Not all lapidary blades are built the same way, and the construction method affects both the kerf width and cutting characteristics. The three main types of lapidary blades—sintered, notched, and ultra-thin—each serve different purposes and have different kerf widths.
Sintered blades have diamonds embedded in a metal bond that forms a continuous rim around the blade. As the metal bond wears away during cutting, new diamonds are exposed, maintaining cutting performance. These blades typically have kerfs in the medium range, around 0.060" to 0.090", and they're popular for cutting a wide variety of materials from soft opals to hard jasper. The continuous rim produces smooth cuts with minimal chipping.
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Notched rim blades have small notches cut into the rim where diamond segments are pressed and secured. These are production blades designed for heavy use. They typically have thicker kerfs, around 0.080" to 0.130", and are built to withstand demanding cutting conditions. The notched design helps with coolant flow and heat dissipation, extending blade life during high-volume cutting. These blades are common in industrial lapidary operations and rock clubs where durability matters more than minimizing material loss.
Ultra-thin blades use a spring steel core with diamond coating on the edge. These blades can achieve kerfs as narrow as 0.1mm (0.004") and are designed specifically for cutting expensive materials where waste must be minimized. The thin profile makes them excellent for precision work but also makes them more prone to deflection and damage. They require careful handling, proper blade alignment, and controlled cutting pressure.
Segmented rim blades, typically used on larger saws (16" and up), feature distinct segments separated by gullets. The gaps between segments allow coolant to reach the cutting surface more effectively and help clear debris. These blades are versatile and can handle both precious and semi-precious materials, though they're more commonly used for larger production cutting where their efficiency offsets the slightly wider kerf.
Why You Can't Just Use Any Blade
The temptation exists to use whatever blade fits physically on the arbor, but lapidary blades and tile saw blades aren't interchangeable even when the arbor size matches. The differences matter.
Tile saw blades are designed for ceramic and porcelain, which have different hardness characteristics than gemstones and rocks. The diamond grit size, bond hardness, and rim design are all optimized for materials that fracture differently than stone. A tile blade used on jasper will cut, but the surface finish will be rough, and the blade will wear much faster than a proper lapidary blade.
The coolant systems differ too. Lapidary blades are designed to run with either water or oil-based coolants, depending on the material being cut. Tile saws typically use water only. The blade materials and bonding agents in tile saw blades aren't necessarily compatible with oil-based cutting fluids used in lapidary work.
RPM specifications also differ between tile and lapidary applications. Using a blade at significantly different speeds than it was designed for can cause overheating, premature wear, or even dangerous blade failure. Lapidary blades typically operate at lower RPMs than tile blades of the same diameter, reflecting the different cutting dynamics of stone versus ceramic.
The arbor sizes between lapidary and tile saws often don't match anyway. Standard tile saws frequently use 5/8" arbors, but some use 7/8" or even 1" arbors depending on the saw size. The blade bushings available for tile saws don't always match lapidary requirements. Even when the arbor size technically matches, the flange design—the washers that secure the blade to the arbor—may be different, affecting blade stability and safety.
Measuring and Verifying Blade Specifications
When you need to verify blade specifications—either to match a new blade to your saw or to confirm what you already have—here's what to measure and where to find the information.
Arbor size is straightforward to measure with calipers or even a ruler. Measure the diameter of the hole in the center of the blade. The most common sizes in lapidary work are 12.7mm (1/2"), 15.875mm (5/8"), and 25.4mm (1"). Some manufacturers print the arbor size on the blade itself, usually near the arbor hole or along the blade body.
Blade diameter is measured from tooth tip to tooth tip across the center of the blade. This should match the advertised size, though older blades that have been resharpened may be slightly smaller than their original diameter. A blade sold as 10" should measure close to 10" across. Any significant deviation suggests either mislabeling or substantial wear.
Kerf width is trickier to measure directly because you're measuring the widest point of the diamond rim. Calipers work, but the rim thickness varies slightly around the blade. The most reliable method is to make a test cut in a piece of soft material and measure the width of the resulting slot. This gives you the actual cutting kerf, which is what matters in practice.
Most quality lapidary blades have specifications printed or stamped on the blade body. Look for text near the arbor hole that lists diameter, arbor size, kerf width, and maximum RPM. This information might be partially worn off on used blades, making it difficult to verify specifications without measuring.
If you're unsure about your saw's arbor size, the saw's manual or manufacturer documentation will specify it. For older or used saws without documentation, you can measure the arbor shaft directly with calipers. Remove any blade that's currently mounted and measure the diameter of the arbor shaft itself. This measurement should match one of the standard sizes.
Matching Blades to Cutting Tasks
Different lapidary tasks require different blade characteristics. The blade that works well for one application might be wrong for another, even if the arbor size and diameter match your saw.
For trimming small stones and preparing cabochon blanks, thin-kerf blades in the 4" to 8" diameter range are ideal. These provide precision cuts with minimal material loss. If you're working with expensive opal or turquoise, an ultra-thin blade with a 0.1mm kerf makes sense despite the higher cost and greater fragility. The material you save on a single expensive stone can pay for several blades.
For slabbing large agates, jasper, and other hard materials in production quantities, thick sintered or notched blades in the 10" to 14" range provide durability and cutting speed. The wider kerf removes more material per cut, but these blades will last through hundreds of slabs without significant performance degradation. Production efficiency matters more than minimizing kerf loss when you're cutting common materials.
For cutting soft, porous materials like turquoise, opal, or softer grades of jade, sintered blades with continuous rims produce the cleanest cuts. The continuous rim minimizes chipping at the edges of the cut, which is critical when working with materials that fracture easily. These materials are typically cut with water as the coolant.
For cutting dense, hard materials like Brazilian agate, petrified wood, or jade, notched or thick sintered blades with oil-based coolants provide better cutting performance and blade life. The notches help channel coolant to the cutting surface and improve debris removal. These blades can handle the higher cutting pressures required for dense materials.
The blade's RPM rating must match your saw's operating speed. Each blade diameter has a recommended RPM range for safe and efficient operation. Using a blade at speeds significantly higher than its maximum rated RPM can cause the blade to overheat, warp, or even fracture. Using it at speeds too low results in inefficient cutting and premature wear. Most lapidary saw manufacturers provide RPM specifications for their equipment, and blade manufacturers include maximum and recommended RPM ratings on the blade or in the product documentation.
Common Blade Sizing Mistakes
The most common mistake is buying a blade based only on diameter without checking the arbor size. The blade arrives, and it doesn't fit. If you're lucky, the blade came with bushings that solve the problem. If not, you're ordering bushings separately or returning the blade.
Another frequent error is assuming that "standard" means the same thing across different types of saws. A "standard" tile blade and a "standard" lapidary blade might share a diameter but have completely different arbor sizes, kerf widths, and cutting characteristics. The term "standard" refers to what's common within a specific application, not a universal specification.
Underestimating the importance of kerf width when cutting valuable material is expensive. The difference between a 0.090" kerf and a 0.1mm kerf doesn't sound like much until you calculate the total material lost across multiple cuts. On a $50 piece of high-grade opal being cut into five slabs, that difference in kerf width could represent $20 or more of lost material.
Buying the cheapest blade without considering the application usually results in poor cuts, rapid blade wear, or damaged materials. Ultra-cheap lapidary blades often use lower-quality diamond grit or inadequate bonding agents. They might cut initially, but they wear quickly and produce increasingly rough surfaces as the diamond grit is lost. For expensive materials, a quality blade that costs three times as much but lasts ten times as long is a better investment.
Ignoring the maximum RPM rating is dangerous. Running a blade faster than its rated speed generates excessive heat, can cause the bond between the diamond rim and the blade core to fail, and in extreme cases can cause blade fracture. The blade's maximum RPM is based on the structural properties of the blade at that diameter. It's not a suggestion.
Resources and Standards
The lapidary community has limited formal standardization compared to other cutting tool industries. Most blade specifications follow general circular saw conventions, but there's no universal lapidary blade standard. Different manufacturers use slightly different specifications even for blades marketed as the same size.
Industry resources like Highland Park Lapidary and suppliers like SUVA Lapidary Supply maintain technical documentation on blade specifications, compatibility, and usage. These companies often provide compatibility charts that match blades to specific saw models, taking the guesswork out of blade selection.
Rock and gem clubs often maintain knowledge bases about equipment compatibility. Members who have worked with various blade and saw combinations can provide practical guidance on what actually works well. Online lapidary forums document real-world experiences with different blade types, including information that doesn't appear in manufacturer specifications.
When manufacturers like MK Diamond or Hi-Tech Diamond publish technical specifications, these documents include arbor size, kerf width, recommended RPM ranges, and coolant recommendations. These specifications should be considered as starting points. Real-world performance depends on your specific saw, the material being cut, and cutting conditions.
Some suppliers offer blade selection services where you provide your saw model and what you're cutting, and they recommend appropriate blades. This service is particularly useful if you're working with an unusual or older saw where finding specification information is difficult.
The key takeaway: when ordering a lapidary blade, you need to know three measurements—arbor size, kerf width, and diameter—and you need to understand how those measurements relate to what you're cutting. The diameter gets the marketing attention, but the arbor size determines whether the blade fits, and the kerf width determines how much material you'll lose with each cut.
If you're setting up for lapidary work and need guidance on saw equipment, understanding these blade specifications helps you evaluate whether a particular saw will work with the blades you need for your projects. The slabs produced by proper blade selection often become raw material for cabochon making, where precise thickness control from blade kerf selection affects the final gem. And if you're expanding your lapidary capabilities into other areas like rock tumbling, the same attention to specifications and compatibility applies across all the equipment. These technical skills—understanding blade geometry, material properties, and cutting mechanics—represent the kind of practical lapidary knowledge that hobbyists now preserve as professional training programs disappear.