1. Definition of Capto
Capto is a double-sided hollow conical positioning tool holder available in seven models: C3, C4, C5, C6, C8, C8x and C100, each corresponding to a different diameter. The cross section of the Capto tool holder features three evenly spaced curved surfaces with three evenly spaced convex edges at 120° intervals around the circumference. This design maximizes contact area, minimizes stress concentrations, reduces deformation and wear, ensures more uniform force distribution, enables better torque transmission and improves positioning accuracy.
2. Interface structure of Capto tool holder
The Capto tool holder has a triangular pyramid structure, as shown in the figure below. Its three convex edges are evenly distributed around the circumference. The convex edges are connected by arcs. The taper ratio of the tool holder is 1:20. After being installed in the spindle, the hollow taper shank is automatically centered in the taper hole of the spindle. The Capto tool holder is installed in the spindle hole. Before the tie rod is tightened, the gap between the tool holder flange surface and the spindle end surface is 0.2mm. Under the action of the clamping force, the hollow taper shank undergoes elastic deformation, which causes the surface of the tool holder flange to be in close contact with the end surface of the spindle, thereby enabling clamping and simultaneous positioning of the conical surface and the end surface.
3. Features of the Capto tool holder interface
Compared with HSK tool holder, the main feature of Capto tool holder is that its cross section is composed of three evenly distributed curved surfaces, and the unique triangular pyramid structure achieves two-way torque transmission without slipping.
The shape of the BB interface in the figure above is defined by the following equation:
As Dm changes, the cross-sectional shape of the tool holder changes as shown in the figure above. It can be observed that as Dm increases, the size of the cross section increases uniformly. If the spindle hole dimensions remain constant, the interference fit between the tool holder and spindle will increase. This improves the connection rigidity and radial positioning accuracy of the Capto tool system. On the contrary, as Dm decreases, the cross-sectional size decreases uniformly. As a result, the interference fit between the tool holder and the spindle is reduced, possibly causing backlash. Reducing the contact area of the tapered surface will weaken the radial positioning effect and ultimately lead to its loss.
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