Inside and out: Turning Performance

When IDs and ODs must be concentric, a combination ID/OD grinding machine might be just the ticket.

Similar to a multitask machine, a machine tool that combines ID and OD grinding enables producing a part in one chucking. This is beneficial when the part requires a high level of concentricity because part refixturing can increase total indicator runout through tolerance stack up.

“If your TIR needs to be in the low tenths, say 0.0002 ” and under, you’d better consider doing all the grinding in one chucking,” said Denny L. Rowe, director of sales and marketing for Weldon Solutions, York, Pa. The grinding machine builder targets production applications and offers the Model 1632 Gold ID/OD CNC grinder.

Courtesy of United Grinding

The workhead on the Studer S41 ID/OD grinder from United Grinding.

In one application, Weldon Solutions reported that Aero Gear Inc., Windsor, Conn., uses the Model 1632 Gold with a 16 “-dia. faceplate for workholding to rework aerospace components with various IDs, ODs, tapers and radii while minimizing setup. The parts manufacturer performs ID grinding with a 30,000-rpm high-frequency spindle. OD grinding, for parts up to 16 ” in diameter and 26 ” long, is done between centers, and a live-spindle workhead accommodates a variety of chucks and other workholders.

Rowe emphasized that job shops, on the other hand, tend to use so-called B-axis ID/OD grinding machines that have multiple spindles on a turret—a universal grinder. “We don’t go after that market at all,” he said. “We strictly go after high-production work.”

Grinding machine builder Usach Technologies Inc., Elgin, Ill., also targets production applications, but doesn’t avoid the job shop market, noted Martin Nobs, the company’s technical director. For example, Usach is building two OD/ID grinders, a 200 OD-L with 80 ” between centers and a 300-OD-L with 135 ” between centers, for a shop that repairs helicopter parts. “They need to be able to regrind anything,” he said. “That is typical of a repair facility.”

Both machine models hold parts between centers for OD grinding and have ID grinding capabilities, Nobs explained. He added that Usach also offers machines more tuned to ID grinding with OD capabilities. On those models, the part is chucked like on a lathe without the need for a tailstock. Most Usach machines have spindle turrets that hold multiple grinding spindles for added flexibility and to allow parts to be completed in one setup.

Courtesy of Usach

A Usach 150 SG machine grinds a transmission part from both sides simultaneously. The right side is equipped with a turret for ID and OD grinding, including part centering and probing. The left side performs an ID and face grinding operation and also has probing capability. Probing on both sides includes the capability of measuring IDs in mid-cycle for correcting size during a cold start.

Using a center-drive, hollow-workhead design, Usach is also building an ID/OD grinder model that enables grinding features on one side of a part with one X-axis and one Z-axis cross-slide and simultaneously grinding features on the other side through the hollow workhead with a second X-axis and Z-axis cross-slide.

A Universal Approach

United Grinding Technologies Inc., Miamisburg, Ohio, specializes in CNC universal grinding machines for ID and OD grinding. One such offering is the Studer S41, which has 10nm scale resolution, a hydrodynamic and hydrostatic way system, axis drives with linear motors and extremely fast direct drive of the B-axis, according to the company. “The hybrid StuderGuide way system allows you to be extremely precise when positioning the slide and grinding to size,” said Hans Ueltschi, vice president, sales, cylindrical division of United Grinding. “That, in conjunction with the linear motors, gives better repeatability and faster movement.”

Ueltschi pointed out that United Grinding originally saw universal grinders as mainly for job shops because of their flexibility and versatility to handle whatever comes through the door, but is witnessing increasing interest from tier suppliers and OEMs, such as in the aerospace and automotive industries. “It’s a trend because of the accuracy requirements for multiple industries,” he said. “It all comes down to getting a part done as complete as possible in one clamping.”

In the job shop realm, Joe Tenebria, owner of Myers Precision Grinding Co. Inc., Warrensville Heights, Ohio, and International Grinding, Richfield, Ohio, noted an ID/OD grinder is advantageous for achieving tight concentricity tolerances on parts such as rings, bushings and spindle shafts. For dimensions and surface finishes, Myers Precision holds tolerances as tight as 0.000050 ” and imparts finishes as fine as 8 µin. Ra. Tenebria pointed out that 40 percent of Myers Precision’s work is thread grinding, 30 percent is OD and ID grinding and 30 percent is machining. “Our main field is thread grinding and everything revolves around it.”

Courtesy of United Grinding

The Studer S41 ID/OD grinder from United Grinding features linear guide ways, shown here with the machine base.

ID/OD grinding can also beneficial when cycle time is long. “You have a much longer setup but the payoff is, with CNC, the machine is doing most of the work, so the operator can run multiple machines,” Tenebria said, noting he has a Studer S40 ID/OD grinder with three grinding wheels. For ID grinding, Myers Precision uses Okamoto semimanual machines in which the user sets parameters such as feed and stroke with the machine’s computer but table motion, for example, is not computer-controlled, Tenebria added. By not being CNC, the machines grind faster because there is no lag time—however short—required for a machine to read the code.

Talk It Up

According to Victor Truelsen, technical sales engineer for Okamoto Corp., Vernon Hills, Ill., the most successful job shops he deals with offer ID grinding. They have a large number of customers with ID work but those customers don’t have enough individually to justify purchasing an ID grinder, which isn’t as common as an OD machine. “They might have 300 customers and each of those customers is sending them 100 to 200 parts a week,” he said.

Truelsen noted Okamoto builds an ID/OD grinder that’s not fully automated. An end user needs to weigh the advantage of grinding a part in one chucking on an ID/OD grinder vs. grinding it on a dedicated ID and dedicated OD grinder and having a quicker cycle time by running two parts simultaneously. “If you have good chucks, you shouldn’t lose concentricity,” he said about grinding on dedicated machines.

Regardless of the type of grinder, Truelsen emphasized that conversational programming is the predominant programming method, especially at job shops, as it suits most workers’ limited experience with G- and M-code programming. That can present limitations when automating a machine because the large number of variables to be input often requires G and M code, but 90 percent of ID and OD grinding can be performed with conversational programming, he added.

Courtesy of Weldon Solutions

On the Model 1632 Gold ID/OD CNC grinder from Weldon Solutions, ID grinding is performed with a 30,000-rpm high-frequency spindle (left), and OD grinding is done between centers.

Because doing everything in code enables more automation, only a small percentage of universal grinders are automated, according to Weldon Solutions’ Rowe. In contrast, he noted the company regularly automates its production grinders and offers two basic styles: a FANUC robot, the recommended route, and a gantry hard tool.

“We have customers who still prefer the old-style gantry, even though they’re paying a little higher price for it, because their service techs and maintenance guys can work on it,” Rowe said. “There are still people who are intimidated, believe it or not, about having a robot in front of a machine tool.”

Pictorial programming also avoids the need to know code. Bruce Hammond, vice president of sales and engineering for Campbell Grinder Co., Spring Lake, Mich., noted the grinding machine builder developed a user-friendly, pictorial front-end interface in which operators select shapes and routines from a series of menus for IDs, ODs, tapers, faces, wheel configurations and more. “It’s custom-written behind the scenes,” he said. “Operators don’t have to know how to write G code.”

For experienced operators and setup specialists who prefer G code, Pick-N-Place “talking” software from Tru Tech Systems Inc., Mt. Clemens, Mich., offers an expert mode they can select, noted Toby Roll, vice president of sales for the grinding machine builder. Otherwise, the software enables operators to select icons and enter values for the pictured part feature, such as a radius, while the software tells them what to do next. “Some almost hate the conversational side because they’re so picky about being able to control the machine through code,” Roll said.

He emphasized, however, that both modes provide the same options and functionality. A conversational screen “is not a dumb-downed screen,” Roll said. “It’s just a different way to show it. The software is catering to left-brain people or right-brain people.”

But the software enables those without any grinding experience to set up and run a machine with only a few days of training, Roll said. “Ask any grinding shop owner what the biggest challenge is and he’ll tell you it’s finding good people.”

Vertical Configuration

Most ID/OD grinding machines have a horizontal axis, but a vertical design is available, which is the case on ones from Campbell Grinder. A vertical axis is advantageous when mounting a heavy part on the worktable because gravity provides assistance. “It’s easier to get the part on center because you lay the part on the table, unlike a part that’s hanging horizontally,” Hammond said, adding that a vertical grinder has a smaller footprint.

Part quality is also a critical factor, according to Hammond. “Without the additional requirements of chucking the part between centers or using a steady rest or tailstock, in most cases, [vertical grinders] produce a part that’s much more accurate.”

A vertical ID/OD grinder is somewhat limited by part length, but Campbell Grinder has built ones for grinding an OD up to 18 ‘, Hammond noted.

Courtesy of Okamoto

Okamoto’s IGM-15NCIII CNC grinder enables end users to grind IDs, ODs and faces in one chucking and has a 10,000- to 60,000-rpm spindle speed.