Xi'an Heaven Abundant Mining Equipment CO.,LTD
A PDC cutter (Polycrystalline Diamond Compact cutter) is the cutting element mounted on a PDC bit body. Its diamond layer — the thin polycrystalline diamond table sintered onto a tungsten carbide substrate — is the component that actually contacts and shears the rock. Understanding the specifications of this diamond layer is essential for selecting the right cutter for a given formation, whether you are drilling water wells, performing geological exploration, or operating rock drilling tools in mining applications.
In this article, we break down the key diamond layer specifications — thickness, cobalt content, diamond concentration, thermal stability, impact resistance, and surface finish — and explain how each parameter affects cutter performance in different drilling environments.
The four-digit code printed on a PDC cutter is the first and most visible specification. It follows a simple convention: the first two digits represent the cutter diameter in sixteenths of an inch, and the last two digits represent the diamond table thickness in thousandths of an inch.
For example, a 1308 cutter has a diameter of 13/16 inch (approximately 20.64 mm) and a diamond table thickness of 0.008 inch (approximately 0.203 mm). A 1313 cutter has the same diameter but a thicker table of 0.013 inch (approximately 0.330 mm). A 1613 cutter has a larger diameter of 16/16 inch (25.4 mm) with a 0.013-inch table.
| Model | Diameter (mm) | Total Height (mm) | Diamond Layer Thickness (mm) | Typical Formation |
|---|---|---|---|---|
| 1308 | 13.44 ± 0.05 | 8.0 ± 0.1 | 2.0 – 2.2 | Soft to medium-hard formations |
| 1613 | 15.90 ± 0.05 | 13.0 ± 0.1 | 2.2 – 2.5 | Medium-hard to hard formations |
| 1913 | 19.05 ± 0.05 | 13.0 ± 0.1 | 2.5 – 3.0 | Abrasive hard formations |
| 1916 | 19.05 ± 0.05 | 16.0 ± 0.1 | 2.5 – 3.2 | Ultra-hard formations in deep wells |
| 1008 | 10.00 ± 0.05 | 8.0 ± 0.1 | 1.8 – 2.0 | Sidetrack or coring bits |
It is important to understand that the four-digit code only defines the physical dimensions — it does not indicate performance, quality, or material grade. Two cutters with the same size code from different manufacturers can perform very differently depending on the specifications discussed below.
The diamond layer thickness typically ranges from 0.5 mm to 3.5 mm, depending on the cutter model and its intended application. This dimension is arguably the most important specification because it directly governs the trade-off between impact resistance and wear life.
Cutters with thicker diamond tables — such as the 1913 and 1916 models — are designed for hard, abrasive formations like granite, quartzite, and interbedded rock. The extra diamond material absorbs impact energy more effectively before the carbide substrate takes the load, reducing the risk of edge chipping and spalling. In deep-well drilling where bit trips are expensive and time-consuming, the longer service life of thicker cutters translates directly into lower operational costs. A thicker diamond table also provides more material that can be worn away before the cutter loses its cutting edge, making these cutters ideal for high-abrasion environments.
Thinner cutters, such as the 1008 and 1308 models, are better suited for soft to medium-hard formations including shale, sandstone, and coal. Because the diamond table is thinner, the residual stress from the high-pressure sintering process is lower, which reduces the risk of internal microcracks. Thinner cutters also tend to have a sharper cutting edge, which improves the rate of penetration (ROP) in softer rock. They are a cost-effective choice when extreme wear resistance is not the primary requirement.
Cobalt acts as the metallic binder that holds the diamond particles together during the sintering process. The cobalt content in the diamond layer typically ranges from 6% to 16% by weight, and it has a direct effect on the cutter's mechanical properties.
Some manufacturers use a graded cobalt distribution — higher cobalt near the substrate interface and lower cobalt at the cutting face. This technique improves the bond strength between the diamond layer and the carbide substrate while maintaining wear resistance at the cutting edge. When evaluating a supplier's datasheet, check whether the cobalt content is uniform or graded, and whether the test method is disclosed.
Diamond concentration is expressed as a percentage of the theoretical maximum diamond density, where 100% equals 4.4 carats per cubic centimeter. In PDC cutter production, concentration typically ranges from 90% to 130%.
Higher diamond concentration (110–130%) provides better wear resistance and is preferred for abrasive formations. However, it also generates more friction heat at the cutting face and increases raw material cost. Lower concentration (90–100%) allows more cobalt binder in the matrix, improving impact resistance — a better choice for hard rock where toughness matters more than wear life.
The diamond grain size is another critical factor. A multi-modal grain distribution — combining fine grains (around 4 μm) with coarse grains (up to 25 μm) — is commonly used in modern cutters. Fine grains fill the interstitial spaces to improve compactness and wear resistance, while coarse grains form a structural framework for impact resistance. This balanced formulation allows the cutter to withstand compressive strengths exceeding 200 MPa without cracking.
Standard PDC cutters begin to degrade when the cutting temperature exceeds 650–700°C. The degradation occurs because cobalt has a higher thermal expansion coefficient than diamond, causing microcracks to form as the cutter heats up during drilling. To address this, manufacturers apply a cobalt-leaching (acid-leaching) treatment to remove cobalt from the surface layer of the diamond table.
After deep cobalt removal to a depth of 0.15–0.3 mm (or up to 0.5 mm for extreme applications), the thermally stable cutter can withstand temperatures of 750°C to 1200°C without significant hardness loss. This is especially important for:
When reviewing a cutter specification, the thermal stability rating should be accompanied by the test method — typically TGA (thermogravimetric analysis) or controlled oven exposure — and the temperature at which the abrasive wear rate doubles relative to room temperature.
Impact resistance is measured by dropping a controlled mass onto the cutter table and recording the energy (in Joules) at which the first spall or chip appears. Standard PDC cutters typically have impact resistance in the range of 15–65 J, while premium impact-graded cutters can reach 40–80 J.
The required impact resistance depends primarily on the formation type:
A reliable datasheet should state the impact resistance in Joules, specify the test method (ｄｒｏｐ-weight or pendulum), and indicate the sample size (n ≥ 5 is standard). Claims of "high impact resistance" without numerical values are not comparable across suppliers.
The cutting face of a quality PDC cutter should be mirror-polished to a surface roughness of Ra ≤ 0.1 μm. A polished surface reduces friction between the cutter and the rock, which in turn reduces heat generation and improves cutting efficiency. The flatness tolerance across the full cutting face should be ≤ 0.01 mm.
Poor flatness — even deviations as small as 0.03 mm — can create localized high-pressure contact points that lead to micro-chipping within the first few meters of drilling. For any bit expected to drill deeper than 200 meters, mirror polish and tight flatness control are not optional refinements — they are requirements for reliable performance.
Additionally, a precision chamfer (typically 0.2–0.3 mm at 45° or 30°) along the cutter edge disperses the initial impact force when the cutter first engages the rock. This chamfer design can reduce early-stage edge damage by a significant margin and is especially important in formations with variable interlayers.
Beyond the raw specifications, a reputable PDC cutter supplier should provide evidence of quality control. Key quality indicators include:
Choosing the right diamond layer specifications is a matter of matching the cutter to the formation and the drilling objectives. Here is a summary decision framework:
| Application | Recommended Size | Diamond Layer Thickness | Cobalt Content | Impact Resistance |
|---|---|---|---|---|
| Water well drilling (soft) | 1308, 1008 | 1.8 – 2.2 mm | 10 – 14% | 20 – 35 J |
| Water well drilling (hard) | 1613, 1913 | 2.2 – 3.0 mm | 6 – 10% | 35 – 55 J |
| Geological exploration | 1308, 1613 | 2.0 – 2.5 mm | 8 – 12% | 30 – 50 J |
| Mining / hard rock | 1913, 1916 | 2.5 – 3.2 mm | 6 – 8% | 50 – 80 J |
| Oil & gas deep drilling | 1613, 1913, 1916 | 2.2 – 3.2 mm | 6 – 10% | 40 – 70 J |
Conclusion
The diamond layer specifications of a PDC cutter — thickness, cobalt content, diamond concentration, thermal stability, impact resistance, and surface finish — collectively determine how the cutter performs in a given formation. The four-digit size code is only a starting point. When selecting cutters for your drilling project, demand datasheets that disclose all seven parameters with numerical values and test methods, not just adjectives. Matching the right diamond layer specifications to your formation is the single most effective way to maximize bit life, maintain ROP, and reduce the total cost per meter drilled.
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