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BT40 Dual Contact Tool Holders
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A standard v-flange tool holder is held firmly inside the CNC machine tool spindle with taper to taper contact. This style tool holder is clamped by a drawbar and has an approximate .125 inch gap between the CNC machine tool spindle face and the tool holder flange. High rpm operation and or high machining loads can cause a standard spindle to expand (bell mouth), which then allows the tool holder to move deeper into the expanded taper, as it is under constant drawbar pressure. This can create chatter, poor concentricity and dimensional inaccuracy of the Z-axis. Tool holders can also stick in the spindle taper causing tool changer faults.
Dual contact tool holders close the .125 inch gap between the tool holder flange and the CNC machine tool spindle face. Their taper diameter and flange face are controlled to a very specific dimension within microns. When a dual contact tool holder is placed into the spindle by hand an actual gap of .0003-.001 inches (depending on machine and spindle size) can be measured. This gap is closed due to the drawbar force, which is between 1,000-2,500 lbs. The spindle is made to elastically deform and the taper will expand until the point in which there is no longer a gap. Thus a very secure connection is made between the CNC machine tool spindle and the tool holder resulting in reduction of chatter and increased tool life. Dual Contact is also referred to as BIG-PLUS® and both are compatible. *BIG-PLUS® is a trademark of Daishowa Seiki Kabushiki Kaisha; Big Daishowa Seiki Co., Ltd., Corp. and is used only for identification purposes. Compatible with BIG-PLUS® spindles, but not licensed.