Hydraulic toolholders
Hydraulic expansion clamping, shank and sleeve compatibility, product-specific runout, and thermal and assembly limits.
Tags: tooling, toolholders, hydraulic-clamping
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Clamping principle
SCHUNK lists the TENDO E compact C6, 3/4-inch bore at ≤3 µm runout at 2.5 × D (47.625 mm), and the SK40, 16 mm bore at ≤5 µm at 2.5 × D (40 mm). Here D is clamping diameter. The products also differ in projection and spindle connection. The figures apply at the stated measurement distances. Tool-tip runout needs the geometry and measurement of the assembled setup. C6 product 206856, SK40 product 1439112.
SCHUNK's illustrated TENDO mechanism uses a screw and piston to pressurize oil. The sleeve deforms elastically to center and grip the tool, and the chamber damps vibration. A separate screw sets tool length. On the illustrated mechanism an Allen key actuates the screw to its mechanical stop. SCHUNK, TENDO mechanism and actuation.
Two manufacturer examples
These SCHUNK TENDO E compact products illustrate why family-wide accuracy claims need limits. D denotes the clamping diameter in the manufacturer's stated measurement relationship.
| Product and ID | Machine interface | Clamping diameter | Projecting length | Listed runout accuracy |
|---|---|---|---|---|
| TENDO EC SCAPTO C6 Ø3/4 inch ×80, 206856 | SCHUNK CAPTO C6, ISO 26623-1 | 3/4 inch | 80 mm | ≤0.003 mm at 2.5 × D |
| TENDO EC SK40 Ø16×130, 1439112 | SK40, DIN ISO 7388-1 AD/AF | 16 mm | 130 mm | ≤0.005 mm at 2.5 × D |
Sources: C6 product 206856, SK40 product 1439112.
Both pages specify h6 tool shanks, allow additional diameters through intermediate sleeves, and publish a balancing grade of G2.5 at 25,000 rev/min or maximum residual unbalance below 1 g·mm. Those are specifications for the named holders, not a complete cutter-and-holder assembly's universal operating speed. C6 specifications, SK40 specifications.
The two rows differ in diameter, length and interface as well as runout. They do not isolate the effect of overhang, establish a stiffness ranking, or predict a finished-part tolerance.
Shanks, reducing sleeves and insertion
BIG DAISHOWA's hydraulic-chuck manual requires h6 shanks and adequate insertion beyond the model's minimum clamping length. It warns that clamping an empty bore or using too little engagement can damage the holder internally. Its English specification permits the stated Weldon DIN 1835 B exception to the restriction on flats; that exception does not qualify all flat or notched shanks. BIG DAISHOWA, Hydraulic Chuck operation manual, English page.
The same manual explains that its straight reducing collets must seat their flanges against the holder face, and that adding them reduces clamping force and runout accuracy. It excludes PJC12 collets. Reducing sleeves therefore change more than nominal bore diameter: their own compatibility and performance limits remain relevant. BIG DAISHOWA, straight-collet limitations.
Check cutter pullout resistance separately from spindle retention. Tool projection and gripping length measure different parts of the assembly.
Thermal design and operating limits
Hydraulic does not imply one common temperature rating. MAPAL's press release dated March 1, 2018 describes additively manufactured hydraulic chucks operating up to 170 °C, attributing this capability to eliminating the temperature-sensitive soldered joint between sleeve and body. That claim concerns the construction described in the release; it does not transfer to a conventionally joined chuck or establish a current product's rating. MAPAL, application-focused clamping technology, dated 01.03.2018, pp. 1–2.
Fluid pressure, sleeve elasticity, joint construction and operating temperature form one physical system. Heat resistance, radial gripping force, axial pullout resistance and allowable speed remain different properties. A balance grade or nominal shank tolerance supplies none of the missing load or temperature limits by itself.
Worked example: interpreting 2.5 × D
Original arithmetic using the named products. For the 3/4-inch holder, the nominal bore is 0.75 × 25.4 = 19.05 mm. Its 2.5 × D relationship corresponds to 47.625 mm. For the 16 mm holder, 2.5 × 16 = 40 mm. The listed accuracy limits convert to 3 µm and 5 µm, respectively. C6 measurement specification, SK40 measurement specification.
These calculations interpret a measurement relationship. They do not turn the gauge distance into a minimum insertion length, maximum cutting-tool projection or error bound at an arbitrary cutting edge. Such extrapolations would need additional geometry and measurement conditions.
Coverage limits
Sources were inspected on November 2, 2026. MAPAL's release prints its date; the cited SCHUNK pages show no issue date. The BIG manual is identified by its operation-manual title, without assigning its download-directory date as a revision date.
This reference covers the hydraulic expansion mechanism and selected manufacturer examples. It does not establish one universal screw torque, minimum engagement, coolant pressure, thermal limit, maintenance interval, assembled runout or cutting capacity. Damping claims describe the mechanism and manufacturer positioning; they do not quantify chatter reduction for an unspecified machine and cut.