ISO 26622-1 Modular Taper Interface with Ball Track System — Shank Dimensions and Designation

ISO 26622-1:2017 specifies the dimensions, tolerances, and designation system for tapered hollow shanks used in the modular taper interface with ball track system — commonly known as the KM or KMTS (Kaiser Modular Tool System) interface. This quick-change tooling system, developed jointly by two prominent tool manufacturers in 1985 and introduced at EMO Milan in 1987, has become a globally accepted standard for both static (turning) and rotating (milling/drilling) applications.

The ball track system’s unique three-point contact design (one face and two taper surfaces) provides exceptional rigidity while enabling tool changes in under 3 seconds — a key productivity driver in modern CNC machining centers.

Shank Size Range and Key Dimensions

Nominal Size (mm)	d1 — Shank diameter (mm)	d2 — Gauge diameter (mm)	l1 — Taper length (mm)	Clamping force range (kN)
32	32	23.9975	20	9–18
40	40	29.9975	25	13–27
50	50	39.9975	32	22–40
63	63	49.9975	40	36–58
80	80	63.9975	45	53–80
100	100	81.9975	50	75–110

Engineering Design Insights

The Three-Point Contact Principle

The KMTS interface achieves its exceptional stiffness through three precisely controlled contact regions: the flange face and two distinct areas on the taper. When the drawbar pulls the shank into the receiver, the taper contacts at two zones (near the gauge line and near the flange), creating a statically determinate system. This three-point contact eliminates the rocking that can occur with single-taper systems, maintaining concentricity below 2 μm even under heavy cutting loads. The ball track itself serves as the locking mechanism — balls are cammed radially outward into a groove in the receiver, generating the axial clamping force through wedging action.

The clamping force must be carefully set within the specified range. Insufficient force reduces system stiffness and risks tool pull-out; excessive force can cause elastic overstrain of the taper, degrading positioning accuracy over repeated tool changes.

Design Features for Automated Tool Change

The shank design incorporates several features specifically for automatic tool changers (ATC): a flange groove (d3) for gripper arm engagement, orientation holes for spindle alignment, and optional balance holes for high-speed operation. The tool changer groove dimensions are critical — the standard defines precise widths (b1 from 8.9 mm to 24 mm depending on size) and depths to ensure compatibility across different machine tool builders’ ATC mechanisms.

Practical Application Guidance

Annex B provides essential recommendations: minimum clamping forces suffice for finish machining with low cutting forces, while maximum forces are needed for heavy roughing operations. Shanks should be through-hardened, and material selection must balance strength, toughness, and wear resistance. The coolant-sealing O-ring (Annex A, fluorocarbon with 90 durometer) is a small but critical component — a failed O-ring allows coolant ingress into the taper interface, leading to corrosion and loss of clamping force.

O-Ring Selection and Maintenance

The O-ring specified in Annex A serves the vital function of preventing coolant from entering the taper interface during high-pressure through-spindle coolant delivery. The recommended fluorocarbon (FKM) material with 90 durometer hardness provides excellent chemical resistance to water-based cutting fluids and maintains its sealing force across repeated thermal cycles. The O-ring dimensions are size-specific (d18 ranges from 15.6 mm for size 32 to 59.92 mm for size 100, with cross-section d19 of 1.78 mm or 2.62 mm depending on size). Regular inspection and replacement of this inexpensive component can prevent costly spindle repairs — a degraded O-ring allows coolant ingress that can lead to fretting corrosion on the precision-ground taper surfaces, ultimately requiring receiver replacement.

For high-speed machining above 15,000 RPM, order shanks with balance holes and specify G2.5 balancing grade. The standard’s size 32 and 40 shanks are particularly popular for high-speed spindle applications due to their lower mass and reduced centrifugal forces.

FAQs

Q1: What is the difference between ISO 26622-1 and ISO 26623-1?
ISO 26622-1 covers the ball track (KMTS) system with a round taper and ball locking mechanism. ISO 26623-1 covers the polygonal taper (PSC) system with a non-round (polygon) cross-section that transmits torque through form lock rather than friction.

Q2: Can KMTS shanks be used for both turning and milling?
Yes, the system was designed from the outset for both static (turning) and rotating (milling/drilling) applications — a key advantage over earlier systems that were optimized for only one mode.

Q3: What O-ring material is recommended?
Fluorocarbon (FKM/Viton) with 90 durometer hardness. This material resists degradation from water-based coolants and maintains sealing force over extended temperature cycles.

Q4: How is the nominal size designation interpreted?
The nominal size (32, 40, 50, 63, 80, or 100 mm) corresponds to the major diameter of the tapered shank (d1). The same size number is used for both shanks (Part 1) and receivers (Part 2) to ensure interchangeability.