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Waurzyniak, Patrick

Faster lathes, turning machines mandate speedier, more efficient chucks

Talk to just about any machine tool operator about chucks and they'll tell you they want faster, stronger chucks. With improved turning machines capable of faster spindle speeds coming on the market, high-speed chucks are becoming more common for many applications. But as much as machinists need speed, factors such as machine tool accuracy, quick-change capabilities, and quality, all remain important.

In workholding equipment, technical developments sometimes lag improvements in the industry's latest machine tool turning centers, lathes, and machining centers. But higher spindle speeds are forcing machine shops to reconsider their chuck requirements.

"There's an old saying that on the workholding side, nothing new has been invented in 150 years-it's actually reapplication of old technology, which is partially true," notes Spencer Hastert, vice president, Kitagawa Division/Sumikin Bussan International Corp. (Schaumburg, IL). "The trends tend to follow lathe technology and cutting tool technology, where I think speed is becoming more and more a factor with higher rpm spindles."

Some extremely fast chucks sporting speeds above 10,000 rpm have debuted in North America, notably the high-speed chuck introduced by The Goss & DeLeuww Machine Co. (Kensington, CD at IMTS last year, but relatively few applications require speeds exceeding the 6000-7000rpm levels typically found in Europe and Asia.

"We're working with [machine tool] builders in Japan, to develop the technology for power chucks with high-speed applications to 10,000 rpm," says Hastert of the jaw chucks which Kitagawa hopes to bring to North America in the future.

High-Speed Hazards. Most applications simply don't require running machines at more than about 6000 rpm, notes Sidney Roth, president of SMW Autoblok Corp. (Wheeling, IL). And going too fast with an unsafe chuck could be very hazardous to shop personnel.

"You run the danger of ripping the bolts right out," says Roth. He recalls an instance where an automotive shop running a machine at 4000 rpm had a small brass part that flew off a chuck and embedded into a nearby steel structure. "Can you imagine something like a workpiece coming out of the machine? None of the machines are built with enough protection for the workers-and here in the US, if someone's injured, the lawyers are going to line up.

"Safety must be a primary concern," adds Roth, noting that not all chuck manufacturers use the same ratings when publishing data on chucks' grip-force curves. Roth says that while SMW Autoblok measures its chucks' maximum rpm ratings at 50% loss of grip force, another competitor's specs assume a 66% loss of grip force, and safety levels differ.

"High speed doesn't have to mean high rpm," Roth states. "I've never sold one for running at 8000 rpm, and we probably sell more 10" [254-mm] high-speed chucks running at 5000 rpm than any other."

Litigation worries may even have prompted some overseas manufacturers to delay marketing their fastest chucks here in the North American market, preferring instead to sell those models in Europe or Asia until the highest speed chuck technologies are proven in the field.

Until then, the fastest chucks most likely are available only from Goss & DeLeuww, which has tested its new counterbalanced chucks at speeds well above what is considered the top-end norm for turning speeds. "We went way past 10,000 rpm, but there's no sense in shouting about that because nobody's got a lathe that could go anywhere near that fast," says Richard Hippner, Goss & DeLeuww's CEO.

Most lathes today run between 5000-7000 rpm, notes Hippner, with some shops turning parts at up to 8000 rpm. "There are a couple of smaller lathes spinning at 10,000, Wasino's got one," he says. "Spinner is developing one. Allied Signal was trying to machine at 8000 and had a terrible time hanging onto the parts, so they asked us if we could provide a solution, which we did, and it's in production testing now."

Faster chuck speeds are becoming more common, but in some instances, high-speed applications may be better suited to collets than the traditional power chuck, notes Hardinge Inc.'s (Elmira, NY) Workholding Engineering Manager Neal Des Ruisseaux. "High speed is definitely a trend," agrees Des Ruisseaux. "There are [highspeed] chucks available that are, even at this moment, ahead of the machines. There is the tendency for machine tools to move to higher spindle-speed capability, and in order to improve productivity, there's probably some market for that high-speed chuck. Whether it dominates or not, that's quite another question."

Accuracy's Critical. Today's shop floor demands not just improvements in a chuck's speed rating, but also in product quality achieved by improved accuracy. "People want to run it faster, but they also want higher and higher quality output," says Brian Lane, vice president and general manager of Logansport Matsumoto Co. (Logansport, IN). "I've been in this business many, many years, and I've seen requirements in turning operations go from maybe 0.002" [0.05 mm] accuracy on dimensions to where these new lathes will hold 0.0005" [0.013 mm].

"That's rather precise, and so this workholding has to improve," says Lane, whose company manufactures chucks, hydraulic cylinders, Neidlein face drivers and rotary tables. "It has to be capable of performing in that same environment, which it will, and so people are working hard, eliminating grind operations in some cases, because the turning centers can do the job. I've seen our workholding have to go in that direction to stand up in the turning environment. You have catalog chucks that'll run 7000 rpm, and they're just standard three-jaw chucks."

Lane sees an emphasis on end-user product quality, plus the elimination of downstream operations like grinding, as keys for the market. "If that customer can accomplish the end result that he needs on the lathe, then he stays away from grinding operations."

Some machining operations simply can't be accomplished at the higher spindle speeds used with the latest chucks. "There will always going to be some exceptions, but I think the more that machine developments move toward higher speed, the shop floor will demand more accuracy," Hardinge's Des Ruisseaux points out.

Given the choice of smaller parts run in short cycles, using a collet might be a superior choice over the traditional power chuck, he adds. "There's the issue of the type of part that you're holding-parts that chucks are typically used on tend to be bigger. It may be a first-operation situation where the part is pretty rough, it may be from bar, it may be a casting.

"You may not need the accuracy right away, and you may not be able to run it at the highest speeds," says Des Ruisseaux, "compared to the situation that exists when some of the operations have been done and you've got a part that's more inherently in balance which can be run at higher speeds."

Maintenance-Free Chuck. Another problem machinists constantly face is keeping chucks free of chips and other debris during machining operations, notes Autoblok's Roth. Since high-pressure coolant at up to 1000 psi often washes away most chuck lubrication during machining operations, and also forces chips and dirt down into the moving parts of a chuck, Autoblok has developed a new completely sealed chuck. The company recently demonstrated the unit at the EMO show in Paris.

Autoblok's new sealed chuck series features sliding jaws and requires no daily maintenance, says Roth. The chucks are completely sealed to resist penetration by fluids, dirt, and swarf, allowing the chucks to maintain lubrication even when used with high-pressure coolants. "The number one effect of highpressure coolant is that within a very short period of time, it blasts away all the chuck's lubricity," says Roth. "Any kind of chuck grease is going to be blown away. Another impact of high-pressure coolant is that it forces chips and swarf into the jaw slides."

Loss of lubrication can quickly lead to high chuck wear or even failure, he says. Likewise, if a chuck's moving parts are contaminated by chips or dirt, the chuck will bind and eventually lose gripping force. Autoblok's new 8.8, 10.6 and 13" (225, 270 and 330 mm) sealed chucks are available in threejaw versions with metric serrated master jaws, and inch serration will be made available in the future.

QuickCaange Chucks. Along with increasing speed, workholding manufacturers constantly strive to reduce customers' cycle times in setups and fixturing. Toward that goal, many chuck manufacturers now tout quickchange jaws on chucks that aim to cut down setup times and boost overall manufacturing productivity.

"Quick change is becoming more and more popular," notes Kitagawa's Hastert. "In the past, quickchange workholding typically has had a couple of problems. It tends to be a little more expensive than the standard workholding, and with any quick-change system, contamination with chips is a big issue.

"With any quick-change system, when you take something off and put it back on, there's always a potential to introduce some sort of contamination that will either affect your accuracy or affect the functionality of the chuck," he adds.

Some observers caution that many workholding users still haven't found the quick-change chuck jaws to be truly effective in boosting overall machining productivity. Hardinge's Des Ruisseaux estimates that from figures he's seen, roughly about 5% of chuck buyers opt for the relatively new quick-change systems, which he says could save some users about one-fifth of the setup time required for changing jaws.

"It does not seem that a high percentage of chuck users want to convert to quick-change usage," says Des Ruisseaux, "and I think that's because the labor savings or setup time reduction isn't great enough relative to the total job that they're doing. They don't deem the economics or the added cost to be particularly worth it."

Using quick-change jaws can be more accurate, however, since the systems include fixed positions for operators to return to, as opposed to conventional jaws, he says. "It's a little bit easier to make a mistake with the conventional jaws," says Des Ruisseaux. "You can miss the serration, and then the part's running out.

"The time-savings benefit may be small potatoes compared to total changeover time, because you've not only got to change over jaws on a chuck, but you're also probably retooling the machine," he adds. "You're setting up the machine, putting all new tools on, loading a new program, so it may be that the savings in changeover time is a small percentage."

Custom Workholding. Along with quick-change workholding, custom workholding solutions have become much more important to customers, and custom workholding is an area where Kitagawa has put particular emphasis, according to Hastert. Pressured by the waves of corporate downsizing over the past two decades, many manufacturing operations that might have employed a full-time workholding expert simply don't have that expertise in-house today, he notes.

"Historically companies would take just the standard chuck that came with the lathe and make it work-they'd do their own workholding," says Hastert. "There's a trend now for companies to realize there may be a better way, by taking advantage of custom workholding. They may contact a workholding house and ask: 'Here's my part; I run 100,000 of these a month. I'm just using a standard three-jaw chuck right now; is this the best way, or is there a better method?'

"With corporate downsizing and a lot of outsourcing, when you go into mom-and-pop shops, a lot of workholding knowledge has been lost," he adds.

In one recent case, trailer-hitch manufacturer Holland Hitch Co. (Holland, MI) kept trying to turn out a 3" (76.2 mm) pin, called a kingpin, that locks into a semi-tractor's hitch to connect its trailer. In order to improve the manufacturing process, Holland switched from its previous lever-style chuck to a Kitagawa wedge-style chuck.

"That's an example of where they used a standard chuck, but the application was so aggressive that they're just beating the workholding to death, they're literally killing it," notes Hastert. Holland decided to employ Kitagawa's N Series Closed Center Power Chucks designed for high-speed, accurate, repetitive chucking.

"Kitagawa's N15 chuck uses a lot less hydraulic input to grip the same part as our previous workholding equipment," says Bill Bushee, Holland Hitch manufacturing engineer. "There's much less wear and tear on a chuck when you compare 8000 lb [35.6 kN] of gripping force to 18,000 lb [80.1 kN] of force."

A major manufacturer of heavy-duty trucking couplings, Holland Hitch annually produces around 200,000 kingpins for trailer manufacturers like Utility and Great Dane. The kingpins generally last for about 500,000 miles before needing to be replaced.

Holland Hitch chose Kitagawa for its combination of quality, price, and delivery, says Bushee. "We expect Kitagawa's N15 to perform for the life of a machine," he says, "but if it lasts only as long as our former chuck, replacement costs would be far less."

Copyright Society of Manufacturing Engineers Sep 1999
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