Dual Contact Spindle System
Design Rivals HSK Performance.

The Big+Plus spindle system is an option being offered by major machine tool builders, especially in Japan, that rivals the performance of HSK toolholders. The Big+Plus spindle system provides simultaneous dual contact between the machine spindle face and toolholder flange face, as well as between the machine spindle taper and the toolholder taper shank. The result is superior rigidity that improves accuracy and surface finish, as well as extends tool life and minimizes toolholder deflection and vibration when used in high speed cutting or for machining in difficult metalcutting applications.

Elastic deformation of each machine's spindle is different and must be carefully measured to determine proper spindle nose dimensions and tolerances by the Big+Plus-licensed machine tool builder.

Also, the machine spindle is protected from fretting corrosion, the repeatability of automatic tool change is improved, and even Z-axial movement during high speed rotation is eliminated since the face contact prevents the toolholder from being pulled up into the machine spindle. In addition the Big+Plus system ensures precision location of the toolholder in the spindle within 1µ (0.000 040´´) when using an automatic tool change for loading tools.

Dual contact is achieved with the Big+Plus spindle system by eliminating the gap or space that generally exists between the machine spindle face and the toolholder flange face. For example, in the case of BT30 and BT40 taper machines, the gap is about 0.08´´ (2mm) and in the case of BT50 taper machines, the gap is about 0.12´´ (3mm). Big+Plus toolholders are manufactured with thicker flanges that eliminate half of the gap. The other half of the gap is eliminated by utilizing machines that have Big+Plus spindles installed in them. The machine spindle face is extended by like distances, 0.08´´ and 0.12´´ respectively, making up the other half of the gap.

The working principle behind achieving dual contact of the face and taper involves utilizing the elastic deformation of the machine spindle to control the gage line accuracy. Because of the pulling force of the pullstud, a machine's spindle will expand from elastic deformation when the toolholder taper comes into contact with the machine. Since axial movement is different on each machine model, depending on the external diameter, rigidity, and clamping mechanism of the machine spindle, the axial movement of each toolholder must be carefully measured to determine the proper spindle nose dimensions and tolerances.

The Big+Plus spindle system is interchangeable with existing toolholders and machines, but to get the best result--dual contact--combination A is the best choice.

With the Big+Plus spindle system's simultaneous contact, machining rigidity is greatly enhanced because of the larger contact diameter of the toolholder flange face. This larger face contact combined with the taper contact works to resist deflection, which results in superior accuracy and finish. Also Big+Plus eliminates Z-axial movement at high rotational speeds--a major cause of poor dimensional accuracy. At high spindle speeds, the mouth of the machine spindle can expand slightly due to centrifugal force. As the machine spindle expands, a conventional toolholder, which is under constant drawbar pulling pressure, moves farther into the spindle. On high tolerance applications, this slight pullback of the cutter can affect dimensional accuracy of the Z-axis and can also cause the toolholder to get locked into the machine spindle taper. The face contact provided by the Big+Plus spindle system prevents the toolholder from being drawn back into the machine spindle.

All tolerances are strictly controlled by high tolerance gages and measuring equipment, which are supplied to machine tool builders, to ensure that dual contact of the face and taper is achieved. Gages are appropriate for CAT-V flange, ANSI B5.50, JIS-BT, DIN69871, and ISO 7388/1 standards. Gages include a master ring gage as a reference dimension between the gage line and spindle face; measuring devices for measuring the distance between the gage line and the spindle face; and master arbor to measure axial movement of the holder.

Another noteworthy aspect of the Big+Plus spindle system is that, unlike the HSK DIN standard, the spindle system can be used interchangeably with existing machines and toolholders. This ensures that existing accessories such as presetters, tooling fixtures, and tooling storage systems can be used with Big+Plus toolholders; nor is it necessary to modify tool magazines and ATC devices of existing machines.

Big+Plus spindles and toolholders close the gap on conventional machines, which is 2mm on BT30 and BT40 taper machines and 3mm on BT45 and BT50 machines.

Another major benefit of the Big+Plus spindle system is the interchangeability with existing CV or BT toolholders and machines. Unlike the hollow shank or HSK-type spindle system, standard CV or BT toolholders can be used in Big+Plus machines. Alternatively, Big+Plus toolholders can be utilized in machines equipped with standard CV or BT spindles. The design of the Big+Plus spindle system allows the user to gain the benefit of Big+Plus tooling without the need to discard existing tooling, which usually represents a significant investment. The Big+Plus spindle system can be used for drilling, end milling, face milling, and boring operations on machining centers with improvements in tool life, accuracy, and quality of surface finishes.

Companies such as Mazak, Okuma, Matsuura, Mitsubishi, Mitsui Seiki, and Takisawa, among many others, are licensed by Big Daishowa Seiki Co Ltd, Osaka, Japan, to offer the Big+Plus spindle system on their machining centers. The Big+Plus system has been introduced to the US by Stanley Sheppard Co Inc, Berlin, CT, which markets and supports Big Daishowa's CNC and conventional toolholders in North and South America.
 

Originally published in the February 1999 issue of Tooling & Production.
Please Note: some pictures or diagrams are only available through the printed media.
 

Buckley Owens Machinery Corp. 6416 Fly Road | East Syracuse, New York 13057 Telephone 315.432.0708 Fax 315.432.0736 Email: info@buckleyowens.com