Today’s Machining World Archive: April 2009, Vol. 5, Issue 04
Boring machines remain vital in recession-proof industries.
Though they don’t boast as many bells and whistles as other, fl ashier machines, boring mills perform machining operations that are in demand across the board in today’s global manufacturing market.
“Every type of big industry out there that uses machinery will sooner or later require a boring mill,” said Bob Conners, vice president of sales and marketing at United Precision Services, Cincinnati, Ohio, an importer of Union Boring Mills.
“They’re precise, intricate, capable machines that have a lot of versatility,” added Greg Morgan, president of job shop CNC Industries Inc., Fairmont, W. Va.
Boring is a machining process in which a drilled hole is enlarged using a single-point cutting tool in an internal turning operation. Boring can be used for roughing or finishing an internal surface. Tolerances are generally held within ±0.002″ to ±0.0005″.
There are two main advantages to using a boring mill rather than another machine tool. In general, they have a larger configurable envelope for a part; very large parts can easily be machined on a boring mill. “Boring mills are synonymous with large envelope work,” Conners said. “So any workpiece that has to be machined and has dimensions beyond about a 60″ envelope is typically routed toward a boring mill, because the traditional horizontal machining centers aren’t built for larger envelopes.”
Another advantage is that a boring machine features a spindle that advances out from its headstock, allowing the end user to reach into small cavities. “With a live spindle you have the opportunity to keep the tooling short from the cutter point to where it fixes to the spindle and you minimize tool deflection,” said Kenneth Campshure, director of sales for boring machine manufacturer MAG Giddings & Lewis, Fond du Lac, Wis.
There are two types of boring mills, horizontal and vertical. On a horizontal machine the spindle is mounted horizontally and on a vertical machine the spindle is mounted vertically. The main difference between the two is that on a horizontal boring mill, the workpiece is stationary and the tool turns, while on a vertical boring mill, the tool is stationary and the workpiece turns. The shape of a workpiece will generally determine if a vertical or horizontal machine is used.
“On a horizontal you have more versatility, because it doesn’t limit your part size,” Morgan said. “You might only be working on three feet by three feet of it but you could put a 10’ tall part on the table, whereas with a vertical machine you could only put maybe a three foot part on the table.”
Despite these differences, vertical and horizontal mills generally see equal amounts of use. John Ilczyszyn, owner of job shop Pride Machine Tool Inc., Melrose Park, Ill., has both types in his shop and finds it difficult to say which is more popular. “All of our machines are busy and we have just as much work on the vertical boring mill as we have on the horizontal boring mill,” he said.
How to Bore
A boring bar consists of an indexable insert, a spindle and an anchor where the spindle is anchored to the machine. The length by which the spindle extends from the anchor is its overhang.
End users seek to limit overhang as much as possible, as the longer a spindle extends from the anchor, the greater the risk of deflection, which can lead to chatter and insert failure. “You’re machining with a flagpole, so the longer the flagpole, the weaker it is,” Campshure said.
Machinists generally judge acceptable overhang by the ratio of overhang to the diameter of the bar, which should be as large as possible. Some peg this ratio at four to one, overhang to diameter. According to Conners, the ratio can go as high as 10 to one, but that would be “absolute worst case.” Ilczyszyn’s shop’s boring mills have bar diameters between 5″ and 6″, and his machinists try not to overhang more than 36″. He says that an eight to one ratio can be achieved without any problems at all.
The diameter of bar on a machine will determine how much horsepower is needed. “A 5” spindle is roughly 50 to 70 horsepower, as you go larger in diameter you can also increase your horsepower,” said Gary Carlson, vice president of machine tool manufacturer WMW Machinery, West Nyack, N.Y.
Where the rubber meets the road on a boring mill, is the insert. What type of insert is used is determined by whether an end user is roughing or finishing. “On the finishing side, we make specific wiper geometries that we refer to as a knife-edge,” said Tony Williams, solutions leader at Sandvik Coromant, Pontiac, Mich. “You get a clean, sharp cutting edge, which allows the boring tool to pass through the bore at a higher feed rate and still generate a nice, smooth surface finish.”
According to Williams, the most popular type of material of boring mill inserts is cemented carbide. The type of insert coating used is determined by the workpiece material that a shop is machining, but Williams noted that aluminum oxide is almost always an ingredient in the coating.
History of Boring
The history of boring mill machines goes back 100 years. MAG Giddings & Lewis built its first boring machines in 1905.
The biggest change in boring mills since they emerged has been their controls. CNC controls were first applied to the machines in the mid-1950s.
“They started as gear-driven, mechanical machines,” Carlson said. “The operator would throw levels to engage clutches and change feed rates, and even have to crank large wheels to move an axis. Now of course it’s evolved to totally CNC-controlled, lights-out type machining. The program is downloaded from the production manager’s office and the operator just calls it up, sets the workpiece and goes on to something else.”
This is due not to just the addition of CNC controls, but also to how motors and drives have increased in quality and speed.
Not all job shops have upgraded to CNC controls. Dusan Radakovic is owner of job shop Field System Machining Inc. in South Elgin, Ill., and he continues to use manually controlled boring mills. He says the one-off, custom nature of his work makes CNC not worth the expense. He asked, “If you want to make just one piece, why would you spend 20,000 for upgrading to CNC?”
Cost and Demand
The cost of a boring mill machine can range from roughly $500,000 to $5 million. Demand for boring mills remains consistent, but since the machines are long lasting and expensive, the market is small compared to other machine tools. Like all other industries, it’s currently somewhat fl at due to the state of the economy.
“Now, at this particular time in the economy, [people are] going to be repairing what they have,” said Campshure, who explained that up until recently people were prone to buy new boring mills because of advancements in technology on the machines and because “the used market was pretty much scarfed up, the good stuff was gone.”
Some manufacturers, however, are not seeing any slowing of sales for boring mills. Ralph Appleby, president of TOS Trade North America, Mt. Juliet, Tenn., a seller of horizontal boring mills, reports having a “guilt complex” over his sales. “Because you hear what’s going on in the country, it’s depressing and I’m thinking ‘But why is business so good for me?’” He offers this explanation: “If you’re in energy, you’re going to be busy, or you should be busy, and a horizontal boring mill really suits itself for energy.”
Boring the World
Boring mills are used to machine parts for use in the energy industry, oil and gas production, windmill manufacturing, mining, printing, chemical processing, aerospace, ship building, communications, construction and even machinery manufacturing itself.
According to Ilczyszyn, the current state of the economy has driven up demand for boring work as it’s led to a shakeout of boring job shops. “A lot of people went out of business and there are not many of us left,” he said. “That’s why we [are getting] a little bit more work than usual.”
A good deal of the work shops see on boring mills are repair jobs, where a part, such as a large shaft or valve, needs to be repaired rather than replaced because of the size and the cost of the component.
“If you think of a digger with a long arm on it, every one of those joints is a shaft and a bushing where it swivels, and those wear out,” Carlson said. “So they use the boring mill to create a straight, larger diameter bore and then install a new bushing and reinstall the shaft.”
Carlson estimates that 90 percent of such parts are sent to a shop for repair. In instances where this isn’t possible, a shop sends its boring mill to the job site and performs the repair onsite. Field System Machining is one such shop that designs and makes boring machines capable of going to a job site.
For such jobs, the shop’s crews may be onsite for two to three weeks in locations all over the world. Frequently the crews are reporting to jobs where the repair needs to be performed immediately, so the shop exercises all possible options in terms of shipping its machinery.
“For example, about a month ago we had to go to Hawaii,” Radakovic said, “and luckily for the customer we were able to put [the boring mill machinery] in two small boxes 48″ long by 10″ high and 30″ wide,” so it could be shipped by plane. In instances where larger equipment is needed, Field System Machining moves its equipment by ship or ground transportation.
A Boring Day
The day-to-day reality of a boring mill shop is often custom machining. Some end users of boring mills are making their own product for resale, but most are taking on contract parts. “In terms of a job shop getting boring mill work, they advertise what they [have], not specifically by brand but by envelope capacity, spindle size [and] spindle power,” Campshure said.
When Field System Machining gets contacted for a job, Radakovic and his staff look at its specifications and schematics to see if they can take it on. If they decide they have the necessary capacity, they decide which machine to use and begin designing custom fixturing.
“When we look at the drawings we have the fixture in our head right away [from] how the piece looks physically,” Radakovic said. Ilczyszyn reports that his shop’s boring mills are used continuously during every shift. Conners feels this level of use is required if a shop is going to own a boring mill.
“If it’s in a shop it has to see use of 40 hours a shift, three shifts a week, because it’s an expensive piece of equipment it’s a big investment,” he said. “Nowadays, as closely as justifications are looked at, you need a full work schedule to justify the use.”
As in other types of industrial manufacturing, good, experienced help is hard to find for boring mills these days. With boring, however, finding a skilled machinist is of paramount importance due to the high cost of parts a shop is likely to run on a boring mill.
“If you have a small machining center and your material costs are $10 then it’s easy to [use] a young man who is learning and can scrap three or four of them before he gets it right,” Conners said. “But if you’re putting a casting that costs $100,000 on a boring mill, you don’t want to scrap that.”
However, as the machines themselves evolve, the level of skill needed to run them is changing. “We find that a lot of old timers who are excellent tool-and-die makers or machinists, are afraid to switch over to a CNC boring mill,” Carlson said. “So the new operators are all younger guys who don’t necessarily have the experience yet, but the machine does a lot of what the tool-and-die maker used to do as far as the calculations and the actual machining and setup.”