1. What Are Capto Milling Tools and PSC Tool Holders?
The term Capto milling tools is widely used in the machining industry to describe a family of cutting tool systems built around a polygonal taper shank coupling — a geometry originally pioneered by Sandvik Coromant under the "Capto" brand name and later standardized internationally as ISO 26623 (PSC — Polygon Shank Coupling). In modern industrial practice, the terms "Capto," "PSC," and "polygon shank coupling" are often used interchangeably to refer to any tool holder system that conforms to the ISO 26623 standard.
Unlike conventional cylindrical or straight-shank tool holders, PSC / Capto holders use a three-lobe polygonal taper profile that simultaneously contacts both the taper surface and the face of the spindle bore. This dual-contact principle is the defining technical differentiator that gives PSC its reputation for outstanding rigidity, torque transmission, and repeatability — qualities that are especially critical in modern high-performance CNC turning centers and multitasking machining centers.
At Jiaxing XiRay Industrial Technology Co., Ltd, established in 2000 and operating from a 30,000 m² production facility in Zhejiang Province, China, the PSC Tool Holder Series represents the pinnacle of the company's precision manufacturing capability. With over 25 years of experience, 8 dedicated production lines, and a 100% in-house manufacturing rate for all core components, XiRay has built a comprehensive PSC product portfolio that covers the full spectrum of CNC machining requirements.
Fig. 1 — Cross-sectional comparison of cylindrical BT/CAT shank vs. PSC three-lobe polygon shank geometry. The three lobes create the self-centering torque-transmission surfaces that distinguish PSC from all other shank types.
2. The Science of Polygon Shank Coupling
The mechanical genius of the PSC / Capto interface lies in a simple but powerful geometric principle: a three-lobe polygon inscribed within a taper. When this polygon is pressed axially into a precisely matching bore, three physical phenomena occur simultaneously, each contributing to the interface's outstanding performance.
2.1 Dual-Surface Contact
Traditional steep-taper holders (BT30, BT40, CAT40) establish contact only along the taper surface. The spindle face and the holder flange remain separated by a small gap, which allows the holder to tip under eccentric cutting loads — a primary cause of vibration and accelerated insert wear. The PSC polygon geometry eliminates this gap: the holder is dimensioned so that both the taper surface and the flanged face make firm contact simultaneously when clamping force is applied. This "two-face contact" doubles the effective support area and fundamentally changes the stiffness of the interface.
2.2 Self-Centering Mechanics
The three-lobe polygon profile creates a natural self-centering action as the taper is pressed home. Each lobe acts as a guide, directing any small radial offset back toward the centreline of the bore. The result is a positioning repeatability of ≤ 0.003 mm (3 μm) — a specification that remains consistent across thousands of tool change cycles, making it practical to rely on stored tool-length offsets in the CNC controller rather than re-measuring after every change.
2.3 Torque Transmission Without Friction Drive
Conventional tool retention systems rely heavily on friction between the taper surfaces to transmit cutting torque. Friction-based torque transmission degrades under repeated clamping cycles and is sensitive to lubrication contamination. In the PSC system, the three lobes act as positive mechanical torque-drive surfaces, transmitting torque through direct geometric engagement rather than friction alone. This means torque capacity remains consistent and predictable throughout the tool's service life, making PSC especially reliable for high-torque roughing operations.
3. ISO 26623 Standard — Sizes, Tolerances, and Compliance
The ISO 26623 standard (formally titled "Tool holders with polygon hollow taper interface — Part 1: Dimensions and designation of shanks") defines the geometric specification for PSC tool holders, including the taper angle, polygon profile, flange dimensions, and clamping thread specifications. Any tool holder and machine spindle both manufactured to ISO 26623 will be dimensionally interchangeable, regardless of the manufacturer's brand or country of origin.
ISO 26623 defines five standard PSC sizes, designated by the bore diameter of the polygon shank at its reference plane:
Table 1 — ISO 26623 PSC standard sizes with indicative torque and speed ratings. Exact values depend on holder design and clamping system.
XiRay manufactures PSC tool holders in all five standard sizes, with complete dimensional compliance verified through CMM inspection during production. Because XiRay controls 100% of its core component manufacturing in-house, dimensional traceability is maintained at every step — from raw material receipt to final inspection before shipment.
4. XiRay PSC Product Families
XiRay's PSC Tool Holder Series is organized into three principal product families. Each is engineered for a specific combination of machine type, operation profile, and production strategy. Understanding the differences between these families is key to making the optimal tooling selection.
PSC One Piece Shank
The PSC One Piece Shank integrates the polygon taper shank and the cutting tool head into a single monolithic component. By eliminating any mechanical joint between the shank and the tool body, one-piece construction achieves maximum static and dynamic stiffness — the theoretical ceiling of what PSC interface rigidity can deliver.
This product family covers a broad range of turning tool configurations, including PCLNR/L-HP2, DCLNR/L, PCLNR/L-M1, PDUNR/L-HP, DDUNR/L, PSKNR/L-HP, DTFNR/L, PTFNR/L-W, and MVUNR/L designations, each encoding the insert geometry, approach angle, hand of cut, and coupling standard. The one-piece design excels in long-overhang applications, deep-bore access, and finish-turning passes where any compliance at the interface translates directly into surface finish degradation.
Best suited for: High-volume production turning with a fixed part number, finish boring, deep internal turning, and any application where maximum interface stiffness is the priority.
PSC Holder for Turning Mills Series
Turning-milling composite machining centers are the backbone of modern precision manufacturing for complex components. These machines alternate between rotary cutting (milling, drilling, tapping) and stationary cutting (turning), demanding tool holders capable of performing reliably in both modes within a single clamping.
XiRay's PSC Holder for Turning Mills meets this challenge through a combination of robust PSC polygon interface geometry (handling milling torque demands), precision-ground tool seats (providing turning geometric accuracy), and integrated internal coolant channels (ensuring effective chip evacuation in both cutting modes). This product family is particularly important for automotive manufacturing of complex housings and shafts, as well as precision parts processing where eliminating re-clamping errors is essential for maintaining geometric form tolerances.
Best suited for: Turning-milling machining centers (MTCs), Swiss-type lathes with live tooling, and any multi-function machining requiring both turning and rotary cutting in a single setup.
Modular PSC Turning Holder
The Modular PSC Turning Holder system decouples the shank body from the cutting head, enabling rapid head exchange without removing the calibrated shank assembly from the machine spindle. A precision-ground coupling mechanism at the head-shank interface delivers positioning repeatability of ≤ 0.003 mm — matching the absolute repeatability of the PSC shank itself — so that stored tool-length offsets remain valid across head changes without recalibration.
This architecture is transformative for job shops and flexible manufacturing systems: instead of investing in a large inventory of complete one-piece holders, a shop maintains a smaller number of PSC shank bodies and a larger assortment of interchangeable cutting heads. The economics are compelling: head replacement cost is a fraction of a complete holder, and changeover time measured in minutes rather than hours of re-qualification.
The Modular PSC system is particularly valuable in medical device manufacturing (small-batch implants and surgical instruments requiring frequent changeovers) and electronics manufacturing (miniaturized components requiring high precision combined with production flexibility).
Best suited for: Job shops, flexible manufacturing cells, prototype production, and any environment where tooling variety and rapid changeover are operationally important.
Fig. 2 — Modular PSC system concept: a single shank body permanently seated in the spindle accepts multiple interchangeable cutting heads. The coupling joint delivers ≤ 0.003 mm repeatability, eliminating the need to re-measure tool offsets after head changes.
5. Key Technical Specifications
The following table summarizes the core performance and dimensional specifications of XiRay's PSC tool holder series. These figures define the performance envelope within which each holder is warranted to operate when installed, operated, and maintained according to XiRay's published guidelines.
Table 2 — XiRay PSC Tool Holder Series key technical specifications. Source: xiray-tools.com/psc-tool-holder-series
6. How to Select the Right PSC Tool Holder
Fig. 3 — Simplified PSC tool holder selection flowchart. For complex applications, XiRay's engineering team is available to assist with detailed application analysis.
Selecting the correct PSC tool holder requires a systematic evaluation of five interconnected factors:
Step 1 — Machine interface confirmation. The PSC size of the machine spindle is the non-negotiable starting point. Verify the spindle designation (PSC32, PSC40, PSC50, PSC63, or PSC80) in the machine's documentation or by directly measuring the spindle bore reference diameter. Using a holder of the wrong PSC size will result in either no engagement or improper clamping, with potentially catastrophic consequences.
Step 2 — Operation type analysis. For dedicated turning with maximum rigidity, the PSC One Piece Shank is the preferred solution. For machines that combine turning and milling, the PSC Holder for Turning Mills is purpose-engineered for this dual-mode requirement. For environments where tooling flexibility and rapid changeover matter most, the Modular PSC Turning Holder delivers the best cost-per-tooling-position economics.
Step 3 — Workpiece material. Titanium alloys, Inconel, and hardened steels generate high heat and cutting forces that demand through-coolant-capable holders and maximum interface stiffness. For these materials, specify a through-coolant PSC holder and size up if in doubt. Softer materials (aluminum, brass, plastics) allow more flexibility.
Step 4 — Overhang evaluation. Any compliance at the tool-spindle interface is amplified by overhang. For l/d ratios above 4:1, prioritize stiffness above all other selection criteria and choose the one-piece PSC shank.
Step 5 — Batch size and changeover frequency. High-volume single-part-number production favors dedicated one-piece holders. Mixed-production and job-shop environments favor the modular system, where the payback period on the shank investment is typically well under one year for shops running more than two job changes per week.
For application-specific guidance, XiRay's engineering team can be reached through the service and support page or directly at sales@xiray-tools.com.
