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Do you want traditional or leading-edge technology? Part two of our toolholder review.
Not long ago, if someone mentioned a toolholder it was a foregone conclusion that they were talking about a CAT steep taper. That venerable design has been a standard in the industry for more than 20 years, and makes up about 70 to 80% of the nation's toolholder inventory. But the move to higher speed machining is changing the game significantly. According to William Popoli, president IBAG Spindle (North Haven, CT): "Speeds over 15,000 rpm are becoming standard, and the venerable CAT and also the well-established BT configurations don't do well at these speeds."
Among the designs to consider are the HSK (covered in our April 1999 article," What's Happening With HSK?"), a German design that has gained wide attention, and proprietary designs from Kennametal (KM), Valenite (RV), Sandvik (Capto), and Stanley Sheppard (Big Plus), a design of Diashowa Seiki (Japan).
For those requiring the stiffest toolholding systems, there are also various hydraulic chuck designs and thermal systems that use expansion and contraction to hold the tool.
When considering all this diversity, Bruce Travis, business manager for connection tooling at Valenite (Madison Hts., MI), notes that, "about 30 years ago companies were dedicated to making specific systems. It's one big supermarket. No one wants to draw the line. If you need it and will pay for it, we will make it.
"One of the problems with toolholder diversity is that a user makes choices without understanding the benefits and limitations of each system," says Travis. "For example, there is no reason to buy a heat shrink system if a collet will do the job. You have to ask yourself, `What are my part tolerances and how does the runout for each type influence that part?"'
Can CAT come back? The initial CAT design was chiefly the result of the Caterpillar Corp. (Peoria, IL) pushing for a standardized toolholder for use in machining centers. The issue centered on the position and shape of the "V" where the gripper held the tool. Gradually ANSI B5.50, which covers both the CAT and earlier BT designs, was developed. (They are interchangeable if hand loaded, but can't be used together in an automatic loading system.)
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