Precision grinding as few as 25 gears at a time becomes profitable by eliminating costly, formed, diamond dressing wheels.
Warren Johnson's GM Goodwrench Service Plus Pontiac runs the quarter mile at an earth-shaking 200.53 mph in 6.883 sec. If a transmission gear has been manufactured with a tooth-form profile out of specification, all that horsepower will eventually find the error, break the tooth, and end racing for the day.
A Gleason TAG 400 grinder features advanced software, a special closed-loop, servo-controlled dresser system, and an inexpensive sintered-diamond disk with a generic 0.025-in. edge radius. It automatically dresses grinding wheels used to modify racing transmission gears, making those short-run jobs profitable for large gear manufactures.
After heat treating, Gleason's TAG 400 CNC threaded-wheel grinder takes off 0.007 in. of stock from this racing gear.
CNC wheel forming on the TAG 400 lets machinists analyze gears from last weekend's race, program profile changes into the dressing system, and have the new gears ready for this weekend's racing.
When the green light flashes, over 1,200 hp and 1,000 ft-lb of rock-crushing torque travels through the transmission of an NHRA Pro Stock car, accelerating it to over 200 mph in under seven seconds in a quarter mile. These transmissions and the gears within must endure this intense abuse time after time without failure.
Because gears only last about 5,000 race miles and each race track demands different sets for top car performance, professional racing is a market the precision gear manufacturer hates to blow by. The only problem is running these 25 to 100-piece jobs in-house without losing money.
One way is on a gear grinding machine that doesn't require costly, formed diamond dressing wheels. A TAG 400 CNC threaded-wheel gear grinder from the Gleason Corp., Rochester, automatically contour dresses wheels using a relatively inexpensive sintered-diamond disk with a generic 0.025-in. edge radius. Showcasing advanced software and a special closed-loop, servo-controlled dresser system, the machine profiles grinding wheels for modifying gears with as small as a 16-diametral pitch.
High-torque/high-speed wheel spindles adapt to a wide range of wheel compositions and bonds, including high-performance abrasives such as SG ceramics. Wheel speed is continuously variable up to 2,500 rpm, which delivers process flexibility along with automatic surface-speed control. Workpiece capacity ranges from 8-in. face widths to part diameters of 15.75 in., and the TAG 400's GE Fanuc 15MB controller permits full CNC control of eight axes.
William Fuss, president of Hanover Gear Manufacturing, Hanover, Pa., states that manufactured (form-specific) diamond dressing wheels can cost $6,000 to $8,000 and take weeks to design and manufacture. Without this cost, he adds, small lot sizes or prototype gear work can be profitable.
"The TAG 400's CNC wheel forming," says Fuss, "lets our machinists tweak gear profiles in a fraction of the time it would take using formed diamond dressing wheels. Our people analyze gears from last weekend's race, program profile changes into the TAG's dressing system, and have the new gears ready for this weekend's racing—all in small lot sizes of 25 to 100 pieces done with precision at a reasonable cost." All of which puts customers such as G-Force Products ahead of the standard transmission-manufacturing pack.
The Annville, Pa., company makes gear sets for a NASCAR-approved transmission. It relies on Hanover to eliminate gear runout and distortion from heat treating while also holding tight tolerances.
After gears are heat treated, Hanover removes approximately 0.007 in. from the gear-tooth surface—not just ground straight across, but rather in a crown-shaped fashion. This crown shape compensates for slight shaft flexing caused by extreme and instantaneous loading of the gear teeth.
When transmission shafts flex, or spread apart, they are no longer perfectly parallel to each other. Gear teeth in contact then take on more load at the corners. A crown shape strengthens the contact area and helps alleviate this problem.
Fuss adds that once a grinding wheel is dressed with the proper pitch, and that gear type will be produced again, Hanover retains the wheel rather than redress it.
But, the TAG 400 can also completely redress grinding wheels, saving the cost of purchasing a new one.
Building a race-worthy transmission
For NASCAR racing, ordinary off-the-shelf transmissions would probably last several laps at best. Replacing gears and servicing these transmissions is a pain. Mechanics must remove the whole transmission, tear it down, put in the new gear sets, and then reinstall. This can take hours.
A fraction of a second can be the difference between first and second place, so most teams will opt for a custom-designed transmission that lets them quickly change and match gears for optimum track performance. Two design features that make it possible are split cases and slip-on gears.
There are only three manufacturers that make NASCAR-approved transmissions, and Leonard Long, owner of G-Force Products, builds the gear sets for one of those companies' products called a T-101, which replaces standard transmissions. Long works with Tex Racing, who owns the transmission case. It's made of magnesium and withstands extreme temperatures, shock forces, and torque loads.
Long also builds a G-Force transmission that is predominantly used in drag racing and road racing. Its split-case design along with gears that aren't pressed on makes for quick ratio changeovers and easy routine maintenance. In demanding NHRA Pro Stock cars and trucks, his gears have proven reliable in handling 5,000 race miles equivalent to 150,000 to 200,000 standard transmission miles.
Standard-transmission gears, says Long, are made to AGMA 10 requirements for automotive use and can't withstand the shock loading and high-torque. Racing gears are produced to a minimum of AGMA 12 specification, and manufacturers hob, heat treat, and grind to meet these requirements. However, adds Long, other proprietary processes bring gears up to his company's level of quality.
He explains that minimizing gear wear is only a beginning concern—a more crucial one is actually gear breakage. For instance, in drag racing, the car is at a dead stop with the engine revving to as high as 10,000 rpm. Drivers quickly pop the clutch, instantly loading torque and inertia directly onto the gear teeth that are in contact.
Long builds transmissions with AGMA 12+ gears in various diameters from 3 in. to as large as almost 5 in. These gears are eight pitch and can have as few as 20 teeth or as many as 35, depending on the ratio needed. Gear-face widths are less than one inch in most cases to reduce parasitic drag in the transmission. In comparison, for a normal application involving over 1,200 hp, gear widths would be almost five times that.
According to Long, the intense stress gears are subjected to further underlines the importance of quality gear teeth. As he remarks, "in NASCAR, statistics show that on average 3% of the cars in a race will drop out with gear-box failure. I want to make sure it wasn't one of my transmissions."