Danobat SL 400

Pendulum grinding (also called CBN crankshaft grinding or orbital grinding) is the technique used to grind eccentric crankpins on a rotating crankshaft. The crankpin rotates in an eccentric circular path as the crankshaft turns — the grinding wheel must continuously follow this eccentric motion to maintain contact. The CNC coordinates the C axis (crankshaft rotation) with the X axis (grinding wheel infeed) so that the wheel tracks the crankpin orbit and grinds at the programmed stock removal rate throughout the rotation. This requires very high CNC interpolation accuracy — the Siemens 840D sl on the SL 400 manages this coordination at 0.0001° C-axis and 0.0001 mm X-axis resolution.

CBN (cubic boron nitride) is the second hardest abrasive material after diamond and is specifically suited to high-speed grinding of hardened ferrous metals. In crankshaft grinding, CBN wheels operate at 80–120 m/s (versus 45 m/s for conventional aluminum oxide wheels) and maintain their cutting geometry for hundreds of crankshafts between dresses — a conventional wheel wears rapidly and requires frequent dressing. The result is consistent journal geometry across large production batches, shorter cycle times (higher feed rates possible at CBN wheel speeds), and predictable tooling cost per part. The higher CBN wheel cost ($5,000–$15,000 per wheel) is offset by the dramatically longer wheel life in automotive production volumes.

The SL 400 handles crankshafts up to 800 mm in length between centers with a maximum throw radius of 200 mm (400 mm total crank throw). Journal diameters from 30–120 mm on main journals and 30–100 mm on crankpins are within the machine's grinding range. This covers 4-cylinder passenger car crankshafts (typically 400–600 mm long, 50–70 mm journal diameter), 6-cylinder car and light truck crankshafts (600–750 mm, 60–80 mm journals), and some smaller commercial diesel crankshafts. Very large diesel crankshafts (marine, locomotive) require dedicated large-capacity crankshaft grinders beyond the SL 400's envelope.

The SL 400 is optimized for crankshaft grinding (main journals and crank pins). Camshaft grinding is a related but different process — camshaft lobes have non-circular, mathematically defined profiles that must be traced precisely, requiring CNC-controlled C-axis and X-axis interpolation with cam profile data. Danobat offers dedicated camshaft grinding machines (NG/NGL series) optimized for camshaft lobe grinding. While the SL 400's CNC architecture (Siemens 840D sl, C+X interpolation) is technically capable of simple cam profile grinding, the machine's setup and tooling are engineered around crankshaft journal dimensions and production workflows.

In-process gauging on the SL 400 uses a Marposs contact gauging head that measures the journal diameter continuously while grinding is in progress. The gauge signal is fed back to the Siemens 840D sl CNC, which uses the real-time diameter data to automatically switch from roughing to finishing feed rates and stop infeed precisely when the target diameter is reached. This eliminates the need for operators to stop the cycle, remove the part, manually measure, and re-grind to size — a critical requirement on automated crankshaft production lines running 24/7. In-process gauging also compensates for wheel wear, thermal drift, and workpiece material variation, ensuring consistent journal diameter across large production batches without manual adjustment.