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24 MMS August 2017 mmsonline.com RAPID TRAVERSE Machining Technology in Brief features with high precision, whether in relation to one another or to any other critical datums. "We can cut at least five machines out of most pro- cesses," Mr. Terry says. In fact, a single clamping can take a gear through turning, internal and ex ternal skiving, milling or drilling around the periphery, and even chamfering and deburring processes that might otherwise require special- ized equipment. "That means zero stackup error," he continues. "Every feature, every dimension, every tolerance—they're all dead concentric to each other." As for precision, testing demonstrates the machines can reliably and repeatedly produce gears to American Gear Manufacturers Associa- tion (AGMA) quality standards of Q11. However, that's not a hard limit, he says, explaining that users in the field must find their own balance between quality and productivity. "If you need that AGMA 14 or 15 spec on every part, and you don't want to waste time in the roughing process, maybe you can just plow through to get the part off the machine and onto a grinder. Or, if you have some tool life and cycle time to burn, you can have finished gears when they come off the machine." Whatever the user's requirements, effective skiving begins with rigidity. Constant contact across wide swaths of the multi-toothed tool and the work creates " tremendous force," he says. Even if that weren't the case, two rapidly s p i n n i n g, c o o rd i n ate d s p i n d l e s wo u l d l e ave little room for deviation from the skiving tool's specified crossing angle and feed rate. Even slight chatter can be sufficient to throw geom- etry out of specification. To avoid chatter, "you want everything that's holding that part to be cased in stone, or in this case, iron," Mr. Terry says, referencing the cast iron construction common to all the company's HMCs. Like the FH-J models on which they're based, GS series HMCs feature double rows of ceramic bearings at the front and back of the spindle and oversized roller bearings on all axes. In fact, aside from the workholding spindle and lack of a pallet system option, the most significant dif ferences between GS series machines and their FH-J series cousins are glass scales and higher-quality axis drives. Capability to synchronize two rapidly rotating spindles is largely the province of the GC70 CNC, as well as the machine's Toyopuc programmable logic controller. "The main thing is the processing speed, the ability to control multiple axes in a full synchronous environment," he says about the combination of these systems. "We're waiting for the material to be removed; we're not waiting for the electronics to catch up to the physics." He adds that fast processing speed is impor- tant to ensure not just proper synchronization, but synchronization at speeds that make HMC skiving cost-effective. For its part, the GS series offers work rotation as fast as 3,000 rpm and tool rotation as fast as 6,000 rpm. Mr. Terry emphasizes that this is fast enough to justify the use of carbide A look at the interior of the GS300H, which accommodates gears ranging to 8.66 inches in diameter and 5.91 inches wide. Other machines in this line include the GS200H, which accom- modates gears as large as 220 mm in diameter and 250 mm wide; and the GS700H, which can accommodate workpieces as large as 27.56 inches in diameter and 19.68 inches wide.