How to Produce a Giant Gear

This novel process uses a horizontal boring mill and special tooling for cutting gear teeth to produce giant gears.

MAG (Fond du Lac, WI) proved it knows how to use machine tools, as well as build them, by developing a process that uses a horizontal boring mill (HBM) and specially designed tools to cut 588 teeth in a 19 m (62.5 ft) diameter gear assembly weighing 60 tons (54,836 kg).

The two-piece gear assembly is made of ASTM A290 steel and consists of a 24-section track that also serves as the base, along with a 12-section upper gear rack. The team designed dedicated fixtures for each operation and special tooling for cutting and finishing the gear teeth on an HBM. “We cut the gear teeth on an unconventional machine,” explains Mark Huhn, a project manager at Fond du Lac factory. “In most cases the tooth involute would be generated by the machine itself, but we used a tool with the involute built into the cutter, which was accomplished by grinding the tooth form into the cutter first.”

The gear teeth were manufactured to American Gear Manufacturers Association (AGMA) Gear Quality No. 6, and the gear was assembled to a pitch diameter concentricity of .8 mm (.031 in). The track, comprised of A148M Grade 620-415 castings, required a special cutter to produce a 2.127 deg surface angle. “The angle was circular interpolated onto the track surface and we designed a special cutter to cut the angle on one of our gantry-type machining centers,” notes Huhn.

GEAR SPECS
For “gear aficionados,” here are some specifications:

• 20 deg full-depth, involute teeth cut in accordance with AGMA 201.02
• Pitch Diameter = 19,016.2 mm (748.6693 in)
• Circular Pitch = 101.6 mm (4.0 in)
• Teeth per segment = 49
• Fillet Radius: 9.702 mm (0.382 in)
• Addendum: 32.3 mm (1.273 in)
• Min. Dedendum: 40.4 mm (1.591 in)
• Backlash: 2.286 mm (0.090 in) on pinion, 2.286 mm (0.090 in) on rack, 4.572 (0.180 in) total
• AGMA Gear Quality Number: 6
• AGMA Gear Accuracy Standard: AGMA 2000-A88
• Face Width = 230 mm
• ASTM A290 GR.3 CL.E
• SUP. REQ. S1, S2, S3 and S6
• Alloy Steel Forging

MAG IAS, LLC, PO Box 590, 142 Doty Street, Fond du Lac, WI 54935, 920-921-9400, Fax: 920-906-2522, www.mag-ias.com.