Collet-style toolholders, which use a nut to push a tool-gripping collet into a mating taper in the toolholder's body, offer versatility and affordability for a variety of machining applications. For high-spindle-speed cutting operations, though, more costly toolholding methods are often required to deliver the balance and tool runout necessary for effective cutting at high rotational speeds. The SINO-T toolholder from Schunk (Morrisville, North Carolina) employs expansion technology similar to that used by high-end hydraulic toolholders at a cost comparable to collet-style toolholders.
Instead of using hydraulic fluid under pressure to provide an equally distributed clamping force about the shank of a tool, the SINO-T toolholder compresses an elastic material concentric to the tool's center line. The material under pressure not only clamps the tool to 5 microns of runout accuracy, but it also absorbs both tool and machine vibrations.
New tool installation is simple. Once a tool is placed in the toolholder (intermediate sleeves can be used to allow a single toolholder to clamp different diameters), an axial stop screw is adjusted for proper tool length. Axial tool length adjustment accuracy is said to be +/-0.005 mm. The tool is fixed in the toolholder by tightening a clamping sleeve with a special C-spanner wrench, forcing the elastic material against an expansion sleeve that presses tightly about the tool's shank. A hard stop prevents toolholder damage resulting from over-tightening the clamping sleeve.
In securing the tool, the clamping pressure also directs any oil or residue on the tool's shank into small grooves machined in the expansion sleeve. This cleans and dries the clamping surface area to eliminate slippage and allows good torque transmission from spindle to tool. The tool can be removed with a counterclockwise turn of the C-spanner wrench.
The toolholding mechanism is completely sealed to allow use with through-spindle coolant tools. The toolholder is available in CAT 40 and HSK-A 63 spindle interfaces and can rotate up to 42,000 rpm.