Assuming that equivalent force is applied to the drawbar, twice as much clamping force is exerted on the flange of an HSK shank compared to a steep-taper shank.
This makes the tool more resistant to bending loads, thus allowing deeper cuts and higher feedrates in milling and boring operations. Higher rigidity also translates to a higher natural frequency for the cutting system.
This allows a tool to be operated at higher speeds before resonance or "chatter" commences. Because tool deflection is reduced, machining accuracy and surface finish also improve. With firm contact between the HSK shank's flange and the receiver, the axial position of the interface remains constant during boring and drilling operations that exert the strongest Z-axis forces.
With its stronger clamping mechanism, HSK tooling is also considerably more resistant to pull-out forces than conventional interfaces. But HSK transfers significantly greater torque than conventional shanks Figure 5, at right. This affects the repeatability of machining operations. Another factor that affects accuracy is tool presetting. With a CAT SK, BT interface, variation between the machine spindle and the pre-setter spindle changes the axial position of the tool tip.
This is particularly true in cases where bell-mouthing of the machine spindle has occurred as a result of wear. Conversely, the HSK interface with metal-to-metal contact both radially and axially maintains a constant tool tip position that does not depend on physical differences between the machine and a pre-setter spindle.
As the HSK connection wears during operation, therefore, the tool's rigidity is affected--but not its static accuracy. The HSK interface also offers some key advantages in relation to high speed machine spindles, tool collisions and maintenance.
Using a conventional interface CAT, SK, BT at spindle speeds greater than 8, rpm, the spindle receiver expands at a much higher rate than the toolholder shank. This causes the shank to be pulled back axially into the spindle under the force of the drawbar. This changes the Z-axis position of the tool tip and often locks up the toolholder inside the receiver, thus making tool-changing difficult.
Conversely, the design of the HSK connection prevents the shank from pulling back into the receiver during high speed operation. When a tool collision occurs using a conventional, steep-taper shank, the potential damage can be considerably greater than is true when using an HSK shank.
With its hollow design, however, the HSK shank acts as a fuse during collisions. When a cutting tool crashes, the toolholder breaks off and protects the spindle, thus reducing repair costs and machine downtime. Although regrinding must be done by a professional, many companies offer this service.
On the other hand, regrinding of an HSK spindle is considerably more difficult, requiring a highly skilled operator, an extremely precise grinding machine and the proper gaging equipment.
Because this work is beyond the capabilities of many machine shops, the cost is higher than is true for regrinding steep-taper spindles.
The tool-changing capability of HSK is another improvement when compared to steep-taper shanks. Because of the short length of the HSK taper approximately one-half the length of a CAT shank and the lighter weight of its hollow shank, tool changes can be completed more rapidly than is true with conventional toolholders.
Part of this time savings results from the fact that the HSK interface does not require a retention knob to clamp the shank. This applies particularly to modern CNC machining centers that are used in flexible manufacturing systems. Under these circumstances, machines may operate at low speed and high torque, as well as high speed and low torque. Because conventional toolholders are clamped from the outside, centrifugal force causes the spindle walls to expand faster in relation to the shank at spindle speeds higher than 8, rpm.
Consequently, the draw bar force pulls the shank deeper into its receiver, changing the position of the tool tip and frequently locking up the tool. The HSK interface is not subject to this problem because of firm contact between mating components.
This contact is enhanced at high speeds because, as the collet segments in the receiver rotate inside the hollow shank, centrifugal force increases the clamping force. Additional Performance Factors. Pull Studs. Mill Toolholding Kits. Mill Workholding Vises. Mill Vise Jaws. Workholding Accessories. Vise Kits. Milling Shell Mill Bodies.
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Please tell the model and the length of the precision test bar your need. All test bar arbors are supplied in a wooden frame to store safely, preventing distortion.
The largest cause of excessive tool wear and cutter bits breakage are directly caused from machine tool spindle runout as well as excessive slop or axial play. The spindle runout test bar can be used to test your CNC machine mills for accuracy and alignments, and also to ensure a stable production environment as well as consistency moving jobs from one machine to another. Spindle runout test bars are easy to use and a fast way to verify your machine spindle is running properly.
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