Kemmler Hydraulic Expansion Chucks

Available Sizes and Part Numbers

Purpose and Application

Kemmler Hydro series hydraulic expansion chucks are designed for installation on CNC milling machines and machining centers with SK spindles according to ISO 7388-1 (formerly DIN 69871). The chucks are intended for high-precision finishing and semi-finishing milling, drilling, boring, and reaming operations where minimal radial runout, high surface finish quality, and maximum tool life are required.

Design and Features

The operation of the chuck is based on a closed hydraulic system with an oil channel. When tightening the clamping screw using a hex wrench, internal fluid pressure elastically deforms the inner steel sleeve, symmetrically clamping the tool shank across the entire clamping length. The oil cushion acts as a damper that absorbs micro-vibrations during cutting, reduces tool deflection, and prevents cutting edge chipping. Radial runout is ≤ 3 µm. Factory dynamic balancing is executed to class G 2.5 at 25,000 rpm. The chucks are equipped with an adjustment screw for quick tool projection setup and a bore for an RFID chip.

Compatibility

Chucks are intended for machine spindles with SK 30, SK 40, and SK 50 tapers (ISO 7388-1 / DIN 69871). Designed for direct clamping of cylindrical shanks conforming to DIN 1835 Form A, B, E and DIN 6535 Form HB, HE (with h6 shank tolerance). Precision reduction sleeves are used to clamp smaller diameter tools or other shank types. Spindle mounting is performed using pull studs according to ISO 7388-3 (formerly DIN 69872).

Selection Parameters

Selection is based on spindle taper (SK 30, SK 40, SK 50) and required DCONWS clamping diameter:

• Direct Clamping: diameters 6, 8, 10, 12, 14, 16, 18, 20, 25, and 32 mm;
• Projection LPR: from 60 mm to 150 mm (including extended series .1 at 110 mm and .2 at 150 mm);
• Coolant Supply: Form AD/B execution (switchable coolant supply through center or flange).

Key Advantages

• Superior Surface Quality: hydraulic system damping properties absorb vibrations during machining.
• Precision Accuracy: radial runout ≤ 3 µm extends cutter life and guarantees exact part dimensions.
• Quick Servicing: tool clamping and unclamping are performed in seconds using a single hex key.
• High-Speed Machining: balancing G 2.5 at 25,000 rpm enables operation at maximum spindle speeds.
• Shank Protection: zero deformation or scratching on tool shanks during clamping compared to mechanical systems.