High Speed and High Velocity Machining
Rotational Speed and Balance
Designing tools for high spindle speeds.
A toolholder is the interface between a precision machine spindle and a precision cutting tool. The toolholder has three base elements; the taper connection, the retaining device and the cutting tool connection.
Taper design principles:
Common toolholders for machine tool spindles today are typically one of two classes of taper; steep taper (Cat, BT, DIN) and hollow taper (HSK). These are taper only contact or simultaneous contact.
Steep Taper:
The most commonly used taper principle. Provides very good durability and excellent dampening characteristics for speeds ranging from very low to moderately high. The typical maximum is 30,000 rpm for 30 taper, 20,000 rpm for 40 taper and 15,000 rpm for 50 taper. At higher speeds the spindle may expand due to centrifugal forces allowing the taper to draw into the spindle. This restricts the practical speeds that steep taper can be used. The length of the steep taper allows for a straight line bending mode based on applied side forces.
HSK:
Due to the face contact (no movement allowed) and the hollow thin wall (expands to fill the spindle) of the HSK design, the spindle speed is not restricted by draw-in of the holder due to centrifugal forces. Speeds for HSK spindles are as high as 40,000 rpm. These higher speed spindles (Form E and F) do not utilize a direct tang drive system and therefore are not practical at lower speed higher force applications. The short thin wall taper and face contact provide a stiffer bending mode at lower forces and a very rapid bending at higher forces. This results in a less dynamic stiffness mode.
Balance Design Principles:
Toolholders are a very important element in the overall performance of cutting tool performance at high speeds. Cutting tool concentricity is generally the most important criteria when selecting the holder to use. Tool, toolholder and machine spindle assembly balance is also an important criteria.
Parlec Parsymmetry Toolholders
are designed for higher machining speeds. All Parlec Toolholders designed for high speed operation are design with Parsymmetry. These include all taper ends (except DIN 69871 on request only), collet chucks, shrink fit, shell mill and power milling chucks.
Balanced Toolholders:
Parlec will precision balance any toolholder to any G class and spindle rpm that is practical upon request. Limits below 2 gm are capable (equipment will repeat to .2 gm) but not practical. Generally the industry is asking for balance grades that are much tighter than provide a benefit to the user. The higher your cutting forces the less impact assembly unbalance will have.
Balanceable Toolholders:
The use of balanceable Toolholders provide the benefit of balance correction, at each assembly, when a precision level of balance is preferred. This solution requires that the user have a balancing machine. Parlec’s radial offset technology provides a non-intrusive low cost precision method of balancing toolholder assemblies.
