Getting a Grip on Rotating Round Tools

Getting a Grip on Rotating Round Tools

Toolholding for rotating round tools—end mills, drills, and taps—continues to evolve with innovative designs aimed at guaranteeing precision, security, and repeatability. As a result, suppliers of toolholding technology have made supporting the precision, security, and repeatability of shrink-fit, mechanical, and hydraulic toolholding the highest priority. You don’t have to look any further than the recent offerings from tooling suppliers to find better ways to improve metal removal rates, part quality, and tool life.

The challenge always is to transmit machining force from the machine’s rotating spindle to a metalcutting tool. Toolholders have a front end to grip the rotating round cutting tool and a back end connection to the machine tool spindle. Back end choices to connect to the machine spindle include CAT (ISO), BT (JIS), HSK (DIN), KM (ISO), and Capto (ISO) standard interfaces and the proprietary BIG PLUS. Each has its particular strengths for milling, turning, and drilling, and each requires precision machining, usually grinding, gaging, and advanced inspection to be manufactured to the required precision specifications.

For front end connection to the cutting tool, there are a number of technologies to choose from that have been developed to meet the challenges of high-speed cutting (HSC), heavy-duty roughing of difficult-to-machine metals like Inconel, and sophisticated toolpath strategies. The main culprit that can lead to catastrophic and costly scrapping of workpiece is tool pullout from the toolholder. One chief remedy that has long been identified as beneficial is high gripping torque. To provide additional security, tooling manufacturers have come up with rather ingenious solutions to guard against the possibility of pullout.

Guarding Against Twisting Cutters Out of Holders

“When you look at toolholders, there are four important considerations: rigidity, accuracy, balance, and security,” said Brendt Holden, president Haimer USA (Villa Park, IL). “If you don’t have good taper contact and a properly made interface, you’re not going to be rigid to start with as far as how you interface with the machine spindle. You need balance so that the toolholder is able to hold the runout accuracy properly, and you need security to prevent tool pullout.

“For a long time, we in the industry talked about high gripping torque for example for our heavy-duty shrink fit chucks. High gripping torque systems of shrink-fit, milling chucks, and hydraulic chucks are all based on a high accuracy friction fit with 360° clamping,” said Holden. “However, if there isn’t a form fit in addition to the friction-fit to prevent the tool from spinning or twisting, the tool could ultimately pull out or begin to creep out even with high gripping torque.”

To counter this tendency Haimer developed SafeLock, which combines a shrink-fit chuck or another high-precision chuck with locking elements. The locking principle results from helical grooves that are ground on the cutter’s shank so that they can interface with the form-closed drivers in the holder. The helical form of the groove protects the tool against overturning and pulling out.

“The modification to the cutting tool shank is straightforward and symmetrical. In fact, cutting tool suppliers have found that they are able to add the SafeLock grooves to standard stock end mills, or even end mills that have an existing Weldon flat,” said Holden. “The grooves don’t greatly affect the balance, which is an issue with the Weldon flat. In fact, the modification keeps the cutting tool stronger since the grooves are very shallow as opposed to a deep Weldon flat cutting through a great portion of half the shank,” said Holden.

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