Making of an Accurate Hole with a Boring Bars

Holding the boring bar
The boring bar deflection is dependent on the bar material, the diameter, the overhang, the size of the radial and tangential cutting forces and the bar holding in the machine. The slightest amount of movement at the clamped end of the boring bar will lead to deflection of the tool. Modern high-performance boring tools deserve to be clamped with high stability so as not to introduce a weak link in the set-up. To start with, it is important that the internal surfaces of the tool clamping arrangement are clean and have high surface finish and sufficient hardness.

The optimum stability-solution for clamping the boring bar is a Coromant Capto integrated tool. For conventional boring bars, solid support is always better than screws acting on the bar, as these may damage the bar. Tuned boring bars should never be clamped by screws. The best stability is obtained with a holder which completely encases the bar. A Vtype bar-holder with screws may be adequate but a cylindrical holder with screws is not recommended.

It is important that the recommendations for length, surface finish and hardness of the clamping of the boring bar are met. The adjoining minimum values are primarily intended for use with tuned boring bars but can be seen as general guidelines. The clamping of the boring bar is a critical stability factor.

To modify a standard boring bar to suit an application, the simplest form of adaption is to shorten a standard bar. As regards tuned bars, the length that can be cut off is limited according to the table. When cutting off a boring bar, the minimum clamping length should not exceed 3 times the bar diameter. All boring bars have through-tool coolant supply via slots, on bars having diameters of 16 to 25 mm and through holes on the 32 to 60 mm range.

More:sandvik.com(SANDVIK – Metalcutting Technical Guide-General Turning)