Single-Pass Bore Finishing From Engis Revs up Productivity for Motorcycle Gear Supplier

(WHEELING, IL) - Tight tolerances are extremely important in gear manufacturing; even more so when those gears are used in performance motorcycle transmissions. Just as important is the ability to manufacture as competitively as possible. This was the position a motorcycle component manufacturer faced recently when they contacted Engis Corp. about single-pass bore finishing.

"The first alternative they considered was installing a number of conventional honing machines, where multiple passes of an expanding mandrel achieves a precision finish," explains Robert Marvin, Engis product manager. "But they also had to be as cost-competitive as possible in producing these parts, which led to our discussing single-pass bore finishing."

The spec requirements for the motorcycle component supplier included removing 0.050 mm of material from a 20-mm gear made of hardened steel (Rc 58-64). Bore tolerance was 0.015 mm, the finish requirement was 0.8 Ra, and cylindricity needed to be held to 0.008 mm.

Conventional honing uses a hone that reciprocates many times while expanding and contacting the cutting stones during each cycle. By comparison, single-pass bore finishing on an Engis SPM-series machine is performed with pre-set barrel-shaped tools that pass once through the bore while the tool, part, or both rotate. Tooling on the Engis machine also features a proprietary slow-wearing diamond coating that together with the single-pass system can achieve bore-finishing tolerances within 0.000020 inches in a single finishing cycle. For the motorcycle component supplier, actual bore tolerance achieved was 0.007 mm, 0.6 Ra finish, and 0.005-mm cylindricity.

With two single-pass Engis SPM machines, each configured with six spindles capable of finishing two parts at a time, the motorcycle components supplier is producing 14,000 gears per day. Where conventional honing machines would require taking the machine out of service every 2,000 pieces to change tooling, the slow-wearing superabrasive diamond coating can routinely finish more than 60,000 parts, even in hardened steel. And since the tooling finishes the full periphery of the bore, interruptions such as keyways or splines do not effect performance.

"The result is much more machine uptime and a tool cost reduction of more than 50% while providing the precision finish these gears require," Marvin explains. "Total perishable tooling costs are approximately one cent per finished gear."

Leader in Superabrasive Finishing
Engis Corp. single-pass bore finishing technology and systems have been adopted by many of the world's leading manufacturers in a number of industries, including automotive and transportation, aersopace, firearms, hydraulics and pneumatics, and gears. Process development, automation, and customized application assistance is always available. For more information, contact Engis toll-free at 1-800-99-ENGIS or visit the company's Web site at

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