The three keys to hole quality are diametral accuracy, form and position, and surface finish. Boring tools are the undisputed king in all of these areas, but they're also one of the slowest methods of hole finishing, and in most cases are limited to 10:1 depth to diameter ratios or less.
Conventional carbide-tipped reamers produce good hole quality, are substantially faster than boring and able to reach much deeper, but they also have an Achilles heel. The steel shank to which the carbide flutes are brazed has a thermal coefficient three times that of carbide, and is subject to growth during machining operations.
Worse, sharpening of these tools often leads to less than desirable results. The mixture of carbide and steel wreaks havoc on grinding wheels, providing a reground edge that is rarely as good as the original tool. Also, PVD and especially CVD coating of reground tools is problematic, because the temperature inside most coating vessels reaches upwards of 530 degrees C (986 F), leading to micro-movement of the brazed carbide flutes.
WIDIA Products Group has addressed these problems and more with its new Top Ream carbide reaming solution. Instead of four to eight (or more) individually brazed carbide tips, Top Ream uses a single carbide disc and brazed joint, providing a strong connection that is virtually immune to thermal effects during machining operations.
WIDIA manufacturing engineer Tom Bobos notes another important advantage of Top Ream's all-carbide tip. "Steel-bodied reamers tend to get banged up on the ends. The center can get nicked or distorted, preventing an accurate regrind. With carbide, you always have a good center to locate on." The result is a minimum of four "like new" regrinds vs. an average of three questionable ones.
However, there's more to Top Ream than its ability to hold an accurate edge. "Overall it's just a better design," Bobos says. "A single piece of carbide is inherently more stable and resistant to vibration. The through-hole style has an 18-degree left hand spiral that does a great job of pushing the chip forward. It's really best in class."
Jerry Hanna, WIDIA Director of Sales Operations, says the Top Ream covers hole diameters up to 42 mm (1.65 in.), with the TRF shank-style starting at 14 mm (0.551 in.), and the TRM modular tool from 20 mm (0.787 in.) and up. "This size range covers the lion's share of requests from our customers," he says. "We also offer a wide variety of custom geometries, diameters, and edge preps, all available in three weeks or less."
One of the best features of the Top Ream is the TRM series' mounting mechanism, which makes simultaneous contact on the cutting head's face and taper. Twist the locking screw and the reamer head pops out, with no need for head to body orientation. This provides a strong, vibration-free, and -- most importantly -- extremely precise reamer interface. "There's virtually zero run out with the modular design," Bobos says. "Once you have everything dialed in, you just put the head on and tighten it down. There's never a need to re-indicate after a tool change."
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