The people at Eppinger GmbH felt very hesitant about the goal Ewe Eppinger had placed on their first Hardinge Super-Precision Quest. This was a big change, and nobody really believed they could replace grinding with turning or hard turning, but it became obvious very quickly that they could do what nobody believed they could do.
DENKENDORF, GERMANY — Uwe Eppinger, president of Eppinger GmbH (founded 81 years ago in 1925), says from day one the company has been making turning center tool holders and tooling systems. The company now has three plants (One in Germany and another two in India) and employs some 500 people. Today the company ships 80 percent to 90 percent of their turning center products overseas.
“When the company was founded,” Eppinger says, “we focused on making static tool holders for lathes. But in the last twenty years, our focus has shifted to driven or “live” tooling that enables today’s multi-tasking turning centers to complete complex parts in one set-up.”
The traditional lathe has evolved into a turning center with both turning and milling capabilities. In fact, today’s multi-tasking machines can not only turn a part, but also mill, drill, tap, and cut off — a list of desired functions that just a few years ago would have been unrealistic.
“What we would have typically done in a machining center, followed by multiple secondary operations and machines,” Eppinger says, “we’re now doing in one machine — a turning center. Making tooling systems for this growing range of turning center applications our specialty.”
It was funny thing, Eppinger recalls, but I met a representative from Hardinge in Europe at an exhibition some years back, and he asked if we were doing hard turning. And we were. Then he explained that Hardinge can do what our current turning centers were doing, only so much easier and much more precisely. So, we tested a Hardinge Super-Precision Quest 8/51 in our plant, and after two weeks we bought it.
His thinking, why should I wait? The Quest did everything Hardinge said it would — and more. Plus, Eppinger believed the Quest held capabilities as yet to be tapped.
His people at that time were very hesitant. This was a big change, and nobody really believed they could replace grinding with turning or hard turning, but it became obvious very quickly that they could do what nobody believed they could do, except Eppinger. And Hardinge, of course.
“The new Quest was running a single shift when I ordered the second machine, not knowing what I would do with it,” Eppinger says. “But we were just so impressed with the capabilities and remarkable precision of the Hardinge that I ordered the second one within a couple of months.”
Today Eppinger employs a total of 4 Super-Precision Quest’s, along with an array of other machine tools from the Hardinge Group.
Hardinge: the right stuff?
Eppinger says his company works with many different turning center makers, but among the rest, only Hardinge is known for its rigidity and ultra precision. “That’s why we chose Hardinge turning centers for very special applications,” Eppinger observes. “The big advantage is that we can finish a part on a Quest, which is not the case with all other turning centers that I know. With a general precision turning center, we can do pre-machining, followed by heat treatment, and then finish grinding. With the Quest turning centers, we can completely finish the same part on the turning center, in a single set up, largely because the axial movement of the machine is so precise.
“If we need a finish dimension within microns, we can do it on the Quest,” he continues. “When the operator plugs in one micron of axis movement, this is what the machine really does. With some other turning centers, if you plug in one micron, either the machine cannot read the instruction, or it moves five microns or more, which is not precise enough for finish work. With the Quest, we plug in one micron and the machine moves by one micron — exactly. No more, no less.”
Hard turning and more
Eppinger says his view of Hardinge machines differs from others in the turning center community. “I have a lot of interaction with Hardinge. I have given presentations in Europe, Asia and in North America on how we perceive the machine and how we are using it. Hardinge turning centers are seen by most to be hard turning machines — which is absolutely true. But I think these machines are much better in life than on paper. There are many machines to choose from if all you want to do is hard turning. What really differentiates the Hardinge from the rest is that the Quest will finish a part in one fixturing and deliver the very highest levels of precision, accuracy and repeatability. So it’s not only a hard turning machine; it is truly a finishing machine.”
A new direction in tool holding
Eppinger explains that until quite recently the tool holding system most commonly in use was the VDI system, which is really just a shank sitting in a machined pocket. It was designed sometime during the 1960s, and it was made for static tool holders on drum-type turrets, and in this arrangement it worked pretty well — as long as your main goal was turning rotating parts. Further, it was known as “quick change tooling.” One could swap tools in and out quickly. However, setting the tools was something else entirely and often took hours once you’d changed them. The result: any gains from “quick change” were quickly lost on the altar of setup and productivity.
Other areas where VDI systems have fallen short include backside machining and the use of “live” tooling. “The VDI system was just not made for live tooling,” Eppinger says. “That’s why we concluded that if you need highly precise, rigid tool holders, we have to look at the way the tool holder is attached to the top-plate. VDI just doesn’t work well enough for today’s needs. We needed a different system. And this system became our ESA system.”
A new design
“Our system is completely different,” Eppinger says. “A couple years back we started from scratch, because it was very obvious that the whole top-plate and tool holder arrangement were not made for real precision work.”
The Eppinger design is one where the position of the tool holders is not dictated by machined tool pockets, but by a patented key and keyway system. Each top-plate has twelve ground keys, and these adjustment keys can be individually adjusted in the Y-axis. This allows adjusting each key to 0 on the spindle centerline. We cannot machine without a tolerance, so we cannot machine at 0, but we can adjust to 0. So we have twelve keys on the machine’s top-plate and each of the keys can be adjusted to 0 on the spindle centerline.
Next, the tool holder itself has a keyway, and the tool holder is pulled against the key on the top-plate to position the tool holder. This is a backlash-free system, so we make sure by the way it’s designed that there is contact between one phase of the key and the keyway. Normally, when you’re working with a key and keyway, you have to make sure that the key itself is a little bit smaller than the keyway, but when there is clearance, then again you can introduce positional inaccuracy. In our case, we’ve designed a clearance-free system because we get contact only on one side of the key, leaving one side of the keyway completely free.
“Without any adjustment, we just bolt each tool holder under the top-plate, and it sits there within microns, station-to-station, to the centerline of the spindle,” Eppinger says. “The tool holder system is highly precise because each cutting tool tip is sitting exactly within two to three microns, which dramatically reduces set-up time. When an operator puts a tool holder under the top-plate he doesn’t even have to check; he knows that his cutting tool is sitting exactly where it is meant to be.”
Another consideration is the way the tool holders are attached to the top-plate. They are much more rigid; they are bolted down with five or six times the force than would be common with VDI. This produces a far stronger and much more precise and rigid arrangement.
Eppinger’s PreciFlex (Precision Flexibility) system is a modular tooling system. You have to think the whole system through, beginning with where the chip is being made. Until now, cutting tools, like a drill, were clamped in most cases with a collet, and while a collet has some advantages — it’s very flexible, for example — it had disadvantages as well. Runout inaccuracy of the collet was a severe limitation.
“We developed a system where all our spindle collet seats have a ground spindle nose with four threads,” Eppinger says, “and against this ground spindle nose we attach an adapter with a cone face contact. The cone of the adapter has the same shape as an ER collet, but in the tool holder we can use either the ER collet, as we have always done, or we can use an adapter. The adapter is bolted down under the spindle and sitting in the ER seat, so it has contact with the ground spindle nose. This gives a very rigid connection between adapter and spindle, as well as extremely high repeatability.
“The big advantage now is that we can leave the tool holder on the top-plate and change only the preset adapter. That adapter can be preset outside of the machine, and we are getting an extremely fast tool change as well as very, very high repeatability.”
The new RS-Series from Hardinge
Hardinge North American turning product manager, Jeff Ervay, has become such a believer in the Eppinger top-plate and tool holders that he pushed hard to make them standard features on the all-new Hardinge RS-Series turning centers. “We set out to design and build the best Hardinge turning center ever…nothing less would do. Therefore we decided early on in our development that, Eppinger products would be required features”, explains Jeff Ervay.
The system Eppinger is supplying on the new Hardinge RS-Series High Precision turning centers consists of the top-plate, the tool holder and the adapter. The Preciflex adapter delivers four times higher clamping force than a collet, for example. And the runout is higher also; the runout accuracy is much higher, so the tool life is much longer, especially at high speeds. The Hardinge RS-Series machines are capable of running 6,000 RPM, and runout is key for the lifetime of the cutting tool.
At a certain RPM, when you’re reducing the runout error by 50%, you’re doubling the lifetime of the tool. That’s why the runout is so important, especially on the new Hardinge RS-Series. They’re getting this high runout accuracy through these highly precise adapters.
The new tool holding system for the Hardinge RS-Series — the ESA top-plate, tooling and PreciFlex adapters — was developed and made on Eppinger’s original four Harding Quests. Today, machining time on almost all parts running on these four Quest turning centers with the new tooling system has fallen greatly — operating and set up time have been reduced by 80%.
Whether a machine costs $30,000 or $50,000 more is not the issue. If you have the product for the machine and you know what you want to do, then price doesn’t matter that much. It’s accuracy, precision, repeatability and flexibility that matter. No one wants to try this turning center or that one, looking for the precision and all the other capabilities the new Hardinge RS-Series have.
“For example,” Eppinger says, “we have the capability to make high precision spindles, and we are eliminating nine work steps per spindle, nine other machines, with a single specially equipped Hardinge Super-Precision Quest. So you can imagine what this means to set-up costs and precision, now that we’re clamping the part just once. In fact, we’re not really setting it up any more. We are leaving the twelve tool holders on the machine, and we are changing the adapters. To change the adapters it takes a minute or so. It depends upon how many you have to change, but the change in itself is something less than 10 minutes, total.”
And what of changing the jaws? “I have limited set-up time to a maximum of 15 minutes. What my operators do is put the first work piece in the machine, push a button and that’s that. And we would normally not see that on other machines.
“With the system we developed for the new Hardinge RS-Series,” Eppinger says, “We know where our tools are sitting, because we didn’t change the tool holder. So there’s no inaccuracy in the system. The operator has confidence in the system. He’s only changing the adapters, and the adapters are pre-set outside of the machine within microns, so why should he check them? He puts the work piece in place, loads the program and pushes the button. That’s it.”
From trial to showroom
It’s been a while since the Hardinge sales rep approached Eppinger about the Hardinge Quest turning center. It’s also been some time since Eppinger took a clean sheet of paper and designed a new tool holding system for turning centers which delivers what the 40 year old VDI system could not — greater precision, repeatability, accuracy, better tool life, faster changeover and increased productivity. When it came time to actually make this new tooling system and roll it out, Eppinger made the parts on Hardinge Quest turning centers. And that speaks to the relationship of the two companies: Hardinge turning centers making the new tooling systems — the ESA top-plates, the tool holders and PreciFlex adapters — seen today on the new Harding RS-Series turning centers.
So it seems only natural that Eppinger would become a sometimes-display site for Hardinge. “When there is a potential customer sent by the Hardinge factory, the nice thing is they come and see what we’re doing and how we‘re using Hardinge and the new tooling system,” Eppinger says. “They look at what kind of parts we’re making, how we’re making them, and they ask a lot of questions. I have not seen a single potential customer who has come here and left our factory without placing an order for a Hardinge. Of course, Hardinge sends only seriously interested people. But once they see the machine run, see how simple it is to handle the system and the accuracy and precision levels that we’re reaching, the visitor places an order before he leaves, always.”