Cranking out power: Drilling Performance

All images courtesy of Pamela J. Tallman

Three axes of movement and ram movement on a Bridgeport milling machine.

The knee casting (lower left), the saddle and knee joined by their dovetails (lower right) and the knee, saddle and milling table together (top).

Eagle Machine Inc., in Abbotsford, B.C., frequently takes on challenging jobs, such as modifying a diving bell for deep-sea submarine rescues or designing and machining a set of solid aluminum wheels for an 800-mph land speed car based on an F-104 jet aircraft. Owner Steve Green said, “People come to us with the craziest things because other people tell them, ‘the only place you can go is Eagle Machine.’ “

One customer needed a durable crankshaft for a 1,000-hp drag racing motorcycle engine. As a result, Eagle redesigned the engine and now produces it as the “Nitro V45.” Based on a 45° V-Twin Harley-Davidson engine, the normally aspirated (nonsupercharged) motor displaces up to 200 cu. in., burns nitromethane fuel and can send a bike through the quarter mile in about 6 seconds, reaching a top speed of 235 mph.

The engine’s block and heads are aluminum, but the crankshaft needs to be made of tougher material. Nitromethane carries its own oxygen and boosts power—and thereby stress on engine components—by a factor of 10. “You are hitting the crank with a big sledge hammer when you pour in nitromethane,” Green said. “The crankshaft is the heart of the engine.”

Accordingly, Eagle Machine determined that the best crankshaft material is EN30B steel alloy from Corus Group in the U.K. Green said the alloy is similar to 4340 steel but has more than 4 percent nickel content, compared to 4340’s 2 percent or less. The alloy’s high nickel content lets the crankshaft endure considerable flexing without cracking, but the increased toughness makes the steel more difficult to machine.

The shop acquires the alloy, in 23- to 25-HRC annealed condition, from distributor Encore Metals as 20 ‘-long, 8⅞ “-dia. bars in minimum shipments of 20,000 lbs. “We make 25 crankshafts at a time and 20,000 lbs. will make four batches,” Green said.

The bar is sawed into 9 ” lengths and chucked on a Daewoo Puma 300L CNC lathe, where half of the part is rough turned from a maximum OD of 8⅝ ” down to a 2.776 ” main bearing journal diameter. For rough turning, Eagle Machine uses a Sandvik Coromant grade-4015 CNMG 433 PR insert, applied at 300 sfm, a 0.150 ” DOC and a 0.018-ipr feed rate. The part is then flipped for similar operations on the other end. Roughing leaves 0.030 ” excess stock on the part for finish grinding after heat treatment.

After rough turning, the crankshaft is moved to a Haas CNC mill where the shop employs ballnose endmills to machine lightening pockets into half of the face of each end of the crankshaft.

Next, the shop rough mills the part’s crankpin on a Takumi Seiki V10 AH vertical machining center fitted with a 4th- axis rotary table. The finished diameter of the crankpin, on which the pistons’ connecting rods ride, is 2.375 “. To hold the part in the mill, “we have a fixture on the rotary table that we chuck onto one journal, and we stick a tailstock into the other journal to give it rigidity,” said CNC Supervisor Dave Krol. A 50mm-dia., square-corner Iscar shell mill, tooled with five Iscar grade-950 inserts, then cuts a space in the middle of the crankshaft, creating two flywheels and the crankpin. The milling cutter is mounted on a 4 “-long extension made of tungsten to provide rigidity and dampen vibration.