The Perfect Gear

More than any other type of machining, gear making
relies on a perfect mix of science and art,” says Bill Tandrow,
Director of Mechanical Engineering at Haas Automation.
“I have a lot of respect for anyone who makes gears,” he adds, in a noticeably
reverent tone. “As much as any of our other efforts, the quality of our gear
making defines the quality of our final product.”
The science part of gear making is evident – it is well established in theory,
with books full of formulas. But it’s the less-apparent half that makes the
dramatic difference. The real art of gear making, according to Tandrow, lies in
careful observation and skillful control of the machining process itself. There’s
no “black magic” required, only complete and dogged attention to detail.
Gears don’t make themselves. While that statement may seem obvious,
the fact is that both cylinders and spheres, the most common bearing surfaces
in mechanics, often do make themselves. Although a machinist’s skill is
required to consistently produce them in exact sizes and finishes, these
shapes exist naturally, and their geometry can be machined accurately using
only the most basic implements and setups. Chuck almost any shape stock
into a lathe, run the cutting tool parallel to the turning axis, and you’ve made
yourself a perfect cylinder.
Spheres are formed just as easily, except in three axes. Early machinists
found they could make precision ball bearings with nothing more
complicated than two rotating grooved plates, a suitable abrasive and lots of
patience. The random rolling of rough blanks placed in the grooves
automatically produced precise spheres. Perfectly spherical rocks have even
turned up in riverbeds, created by nothing more exotic than a combination of
the river’s current and a hollow depression in the hard bottom.
But, while cylinders and spheres are natural shapes, the involute gear
tooth is anything but. Even with modern CNC machines to tackle the
problem, skill and careful attention are required to get it right

“From the beginning,” Tandrow continues, “this company’s success
has been built on attention to detail – not just being detail-oriented,
but having the observational talents to see and understand what’s wrong,
and then having the know-how to make it right. That is the single bona fide
secret to producing perfect gears.”
Haas Automation approaches gear making seriously. The company
machines every high-precision spur gear, worm and worm gear for its
extensive product line in-house at its huge manufacturing facility in Oxnard,
California. Out of more than 600 skilled machinists and assembly specialists,
only a handful are assigned the task of making these demanding parts.
Consummate machinists Boris Klebanov and Edik Beginian have been
with the company for about as long as anyone can remember. They
purportedly learned most of what they know about gears from company
founder Gene Haas.
“Years back, when we first started making mills,” recalls Edik, “Gene
wasn’t completely happy with the gears we were getting from vendors, so he
purchased a Reishauer RZ-80 and started making the gears himself. He did a lot
of experimenting and testing to figure out exactly what was going on. He not
only solved all of the performance problems, but he learned how to repair and
maintain the machine himself. Then he taught us.”

“We use those same perfected techniques today,” Boris
adds. “We’re making essentially the gears that Gene evolved,
along with 70 or 80 other kinds of gears. We’re still doing
everything in-house, and we’re still solving all of our
problems ourselves.”
With schedules demanding different machine setups
daily, maintaining process control is just one of many
demands facing these highly talented machinists – but it’s
a big one.
“Spur gears were never intended to be precise,” Tandrow
remarks. “Until recently, nobody had equipment to make
them precise. Machinists were often happy if they just fit
together. If you open a Machinery’s Handbook to the section on
spur gears, you’ll find a lot of tables for backlash and things.
Those tables weren’t based on a desire to make a bad gear,”
Tandrow says. “It’s just that when those tables were written,
back around World War II, that was the state of the art. CNC
gear-hobbers and grinders obviously didn’t exist then. You
just couldn’t expect to hold 30 millionths of an inch on a grind.
But now we have equipment and processes that can hold
down in those ranges repeatedly. We can literally produce an
oil-film fit. We manufacture smoother running gears than
anyone could even have imagined back then.”
Why does Haas insist on making its own gears?
“Because,” says Tandrow, “quite simply, it allows us to
precisely control the outcome. There are so many little tricks
and subtleties in the hobbing and finish grinding, that we
just would not succeed by having them done externally. We
build our own gears to get exactly the right thing for us, at
the highest precision possible.”
Straight-cut spur gears are the basis for all of Haas
Automation’s gearboxes. The company started out buying
complete assemblies, but they just weren’t as perfect as
the engineers wanted them, explains Tandrow. “Finally,
we just designed our own gearbox. Now we make every
part ourselves.

“When you buy gears from someone else,” he
continues, “you effectively have to buy through a
middleman. Even if their shop is just across the street,
you’ve got to build a relationship with them. You’ve
got two different companies, two different cultures,
and you probably have a pretty big disjuncture
between the process of using the gears and the process
of making them.
“But when you make a gear in-house, you can
build things into it that they can’t do across the street.
For example, you can preassemble the gears in a rough
state on a single mandrel, put them into a hobber or a
grinder, and finish-grind them perfectly. The gears are
as exact as you can measure them, and they’re already
on the shaft they’ll run on. ‘Across the street’ is just not
close enough to ensure this kind of quality,” Tandrow
says. “For most of our gearbox operations, the operator
who hobbed or finish-ground the gear is literally within
a hundred yards of where we assemble the gearboxes.
“For a manufacturing environment, that’s the
ideal. We can make the gears in very tight batches of 10
or 20, and quickly process them through. It’s more costeffective
than ordering big batches, and if there are any
issues, we’re only looking at a small number of
reworks to get production flowing again. That’s if there
are any issues,” Tandrow emphasizes. “Honestly,
we’ve not had one since we adopted this approach.”
In the same area where the spur gears are cut and
ground, Haas also machines precision worm gears and
worms for its rotary products. This is where the
dedication to tight process control really pays off.
“The aluminum-bronze worm gears at the heart of
our rotary products are actually quite mature
concepts,” explains engineer Thomas Velasquez, who
has been designing these products for more than a
decade. “The inherent accuracy is assured by the singlelead
hobbers that we use, and by the preassembly we
do before cutting. We place the shrink-fit gear blank
onto the spindle, mount it on the fixture and actually
tram it in. The guys (Boris and Edik) try to shoot for a
runout of about 50 millionths.” This procedure ensures
that the pitch diameter of the finished gear is perfectly
concentric with its mounting diameter.
Again, the inherent accuracy of the setup is
translated into actual product accuracy through the
skill of these machinists, and through their careful

control of the process. “Every third or fifth one is checked on
the Klingelnberg gear analyzer against a master worm,” notes
Velasquez. “We can verify tooth-to-tooth and overall pitch
accuracies on both the worm and the gear at the same time.
We also have special worms that we use to check the gears as
we’re cutting them, for more immediate feedback. We need to
know that they’re coming out of the machines right.”
“That’s another very important aspect,” adds Tandrow.
“You can’t compete at the level just described without having
some of the best equipment in the world: like the Reishauer
RZ-362A hobber, the Studer S40 grinders and the exceptional
inspection equipment we have on the floor. You have to have
the best tools to generate these results repeatedly.”
“We also have new Mitsubishi GC15 and GC40 gear
hobbers,” adds Velasquez, “as well as high-quality carbide
hobs, and a real passion for maintaining the equipment so
that it stays accurate.”
Another factor critical to the accuracy of the gears is the
careful process of heat-shrinking the worm gear to the
spindle before cutting it. “That all but eliminates
concentricity errors,” says Velasquez, “and it simply could
not be done if the gear was jobbed out. In a nutshell, we keep
tabs on everything: We know where we’re going and how to
get there.”
“That’s the complimentary part,” says Tandrow. “We
have an assembly staff that can inspect as they build. Since
the parts are made in a controlled process, and the assembly
staff knows all aspects of it, including the tolerance bands for
testing the parts, we have complete control of the quality.”
Akey member of that assembly staff, Misha Brkic, uses a
proprietary inspection setup to verify the accuracy of each
final product. With his years of experience, though, he can tell
almost as much with his hands during the assembly process.
He knows perfectly the subtle feel of an exactly machined
worm and gear, and can stop the assembly process almost
before it starts if he finds anything unusual.
“This level of skill and experience is the final key to the
success of the process,” says Tandrow. And while Brkic
performs his duties on the opposite side of a long wall
separating the machine shop and assembly areas at Haas, he’s
still only a hundred yards from Boris and Edik. There’s a
large doorway conveniently located midway between them.
“It’s perfect!” Tandrow exclaims with a smile. “Just like
the gears.”

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