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ISO 26623-2:2014 — Polygonal Taper Interface — Part 2: Dimensions and Designation of Receivers
Standardised dimensions and clamping force requirements for polygonal taper interface receivers
1. Standardised Dimensions for Polygon-Receivers
ISO 26623-2:2014 specifies the dimensions of polygon-receivers (sockets) for automatic and manual tool exchange on machine tools such as turning machines, drilling machines, milling machines, turn/milling centres, and grinding machines. The polygonal taper interface (PSC) with flange contact surface transmits torque through form lock rather than friction, providing higher positional repeatability and greater torque transmission capacity than conventional steep taper (BT/SKT) or hollow shank (HSK) interfaces. The standard is prepared by ISO/TC 29, Small tools, and is the second edition replacing ISO 26623-2:2008 with technical revisions covering updated dimensional tolerances and expanded receiver size range.
Eight nominal sizes are defined: 32, 40, 50, 63, 80, 80X, and 100 mm. Each size specifies critical dimensions including the polygon major diameter (Dm), gauge length (l2), taper length (l3), and the offset of the polygon curve (e). Tolerances follow ISO 2768-1 class m for linear dimensions and ISO 2768-2 class K for geometrical tolerances. The polygon profile is defined by a theoretical curve with a ground curve offset of +0.015/+0.005 mm for precise fit. The polygon profile consists of three equally spaced lobes that provide three-point centring and torque transmission through the full 360-degree interface, a key differentiator from traditional two-flat or keyway designs.
| Nominal Size (mm) | Dm (mm) | l2 +/-0.1 (mm) | l3 +/-0.2 (mm) | e (mm) | Clamping Force (kN) |
|---|---|---|---|---|---|
| 32 | 25.2 | 2 | 22 | 0.7 | 15 |
| 40 | 31.6 | 2.5 | 28 | 0.9 | 20 |
| 50 | 39.2 | 3 | 35 | 1.12 | 25 |
| 63 | 48.5 | 4 | 44 | 1.4 | 30 |
| 80 | 60.8 | 5 | 55 | 2 | 40 |
| 80X | 60.8 | 5 | 55 | 2 | 40 |
| 100 | 79.4 | 6 | 72 | 2.8 | 60 |
2. Clamping Force Requirements and Designation System
The clamping system must provide sufficient force to ensure flange contact and elastic deformation of the taper for proper seating. Recommended clamping forces range from 15 kN for size 32 up to 60 kN for size 100. These values ensure that no less than 80% of the total clamping force acts on the flange surface, which is decisive for interface stiffness. For light machining operations such as finishing cuts, lower forces within the tolerance range may suffice, while heavy roughing operations require the upper end of the range to prevent any micro-slip at the flange interface.
Variations in taper shank and receiver dimensions within specified tolerance limits will cause the proportion of clamping force acting on the flange to vary. The manufacturer should provide information regarding permissible speeds, torque transmitting capacities, and bending load limits for each receiver size. The standard explicitly warns that deviation from the specified force range can lead to reduced positioning accuracy, accelerated wear of the polygon profile, and in extreme cases, tool pull-out during heavy cutting operations. Proper lubrication of the taper interface is essential for consistent clamping force and prevention of fretting corrosion at the flange contact surface.
The standardised designation follows the pattern: POLYGON-RECEIVER ISO 26623-2 — PSC [nominal size]. For example, a size 32 mm receiver is designated as POLYGON-RECEIVER ISO 26623-2 — PSC 32. This systematic naming ensures unambiguous communication between tool manufacturers and end users globally.
The 80X size shares the same Dm (60.8 mm) as the size 80 but is designed for higher torque applications requiring a larger shank diameter (100 mm), bridging sizes 80 and 100. This special size was introduced to meet intermediate heavy-duty machining requirements where a full size 100 interface would be oversized and cost-prohibitive.
3. Engineering Design Insights for Machine Tool Spindles
The polygonal taper interface represents a significant advancement over traditional toolholding systems. Unlike steep taper (e.g., ISO 40/50) or HSK hollow shank interfaces, the PSC design uses a ground polygon profile with a defined offset curve (e) that provides form-locked torque transmission. This eliminates dependency on friction alone, reducing the risk of slip under heavy cutting loads and improving process reliability in automated machining cells. The three-lobed polygon profile provides inherent self-centring capability, achieving typical run-out accuracy of less than 3 micrometres at the gauge line.
Annex A provides informative recommendations on permissible speeds, torque capacities, and bending loads. Manufacturers should specify these parameters for each receiver size. The flange contact surface is critical for bending stiffness, and the clamping force must be sized to maintain at least 80% of the force on the flange under all tolerance conditions. The polygonal taper design also offers improved run-out accuracy compared to conventional interfaces, contributing to better surface finish and tool life in precision machining operations. The symmetrical three-point force distribution of the polygon profile minimises deflection under radial cutting forces, a significant advantage for long-reach tooling applications.
From a manufacturing perspective, the polygon profile requires precision grinding with CBN or diamond wheels to achieve the specified surface finish and offset tolerances. The ground curve offset of +0.015/+0.005 mm demands careful process control and frequent gauging during production. The surface roughness specification for the polygon profile is typically Ra 0.4 micrometres or better, achieved through sequential rough and finish grinding passes with controlled spark-out cycles. Regular inspection of the polygon profile for wear, verification of clamping force, and cleaning of the flange contact surface are recommended maintenance practices. The receiver bore should be protected from swarf and coolant ingress during operation to prevent damage to the precision-ground surfaces.
Position pins may be omitted in some designs, but careful consideration of anti-rotation requirements is essential. The surface roughness of the polygon profile must be held to tight tolerances. Surface finish requirements are specified in micrometres and must be verified during receiver manufacturing using profilometry or optical surface measurement.
4. Frequently Asked Questions
Q1: What is the difference between ISO 26623-1 and ISO 26623-2?
Part 1 covers dimensions and designation of shanks (tool-side), while Part 2 covers dimensions and designation of receivers (spindle-side). Both parts must be used together for a complete interface specification. ISO 26623-1 specifies the shank dimensions that must mate with the receivers defined in Part 2.
Part 1 covers dimensions and designation of shanks (tool-side), while Part 2 covers dimensions and designation of receivers (spindle-side). Both parts must be used together for a complete interface specification. ISO 26623-1 specifies the shank dimensions that must mate with the receivers defined in Part 2.
Q2: Can PSC interfaces replace HSK or steep taper in existing machines?
Retrofitting is possible but requires spindle modification and careful evaluation of the existing machine’s speed and torque capabilities. The PSC interface offers higher torque transmission and better repeatability, making it particularly advantageous for high-precision and heavy-duty machining centres where tool retention reliability is critical.
Retrofitting is possible but requires spindle modification and careful evaluation of the existing machine’s speed and torque capabilities. The PSC interface offers higher torque transmission and better repeatability, making it particularly advantageous for high-precision and heavy-duty machining centres where tool retention reliability is critical.
Q3: What is the significance of the 80X special size?
80X uses a 100 mm shank diameter but maintains the same polygon profile as size 80, providing intermediate capacity between sizes 80 and 100. It was developed to address specific heavy-duty applications where a full size 100 interface would be oversized.
80X uses a 100 mm shank diameter but maintains the same polygon profile as size 80, providing intermediate capacity between sizes 80 and 100. It was developed to address specific heavy-duty applications where a full size 100 interface would be oversized.
Q4: Are there any special maintenance requirements for PSC receivers?
Regular inspection of the polygon profile for wear, verification of clamping force, and cleaning of the flange contact surface are recommended. The position pins and taper surfaces should be checked periodically for damage. The receiver bore should be protected from swarf and coolant ingress during operation.
Regular inspection of the polygon profile for wear, verification of clamping force, and cleaning of the flange contact surface are recommended. The position pins and taper surfaces should be checked periodically for damage. The receiver bore should be protected from swarf and coolant ingress during operation.
