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The Essentials of Tool Balancing

Bill Koenig
By Bill Koenig Senior Editor, SME Media

For some job shops, the question is whether to go with tool balancers or not

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Axel Wagner of Allied Machine & Engineering using a tool balancing machine.

Balanced toolholding assemblies, with even weight distribution, operate better. Unbalanced assemblies may experience vibration and shorter tool life, which are amplified by high machining speeds. While reducing spindle speed can lead to smoother cutting, it also decreases metal removal rates and productivity.

The question for some job shops is whether tool balancing machines are worth the additional cost. Companies that produce tool balancers make the case it is.

“Often, the reason a shop may opt to use a tool balancer comes down to dollars and cents—the initial investment cost,” said Matt Brothers, Industry 4.0 tech manager for Zoller Inc., Ann Arbor, Mich. “What is often overlooked in these cases, though, is the increased productivity and quality, and the reduced machine wear offered to shops using a tool balancer,” he added. “Tool balancers save money over time by reducing costs.”

Brendt Holden, president of Haimer USA LLC, Villa Park, Illinois, said some job shops resist the idea of tool balancers. “People will say, ‘I’m still making parts. Why should I add to the complexity? Balancers aren’t producing parts. I’m getting by OK without it, so why do I need it?’” he said.

The executive said tool balancers can improve performance at various speeds. “You can get more productivity with the machines that you already have,” he said. Customers without tool balancers “don’t know the productivity they are missing.”

Some cutting tool makers say they’ve improved the process of prebalancing tools. “We have two steps to our balancing process,” said Michael Schuffenhauer, senior global manager of tooling systems for Kennametal Inc., Pittsburgh. “The first step is balancing the tool during the design phase by carefully controlling the weight distribution. The second step is fine balancing toolholders that require higher quality to a [balancing grade of] G 2.5 – 25,000 rpm specification during the manufacturing phase. Our toolholders are well-balanced before being shipped to the customer.”

The Basics of Balancing

Tool balancing is generally performed with weighted balancing screws. It is the last step in the process before the assembly is sent to a machine. Necessary offset measurements defined by the presetting operation are uploaded directly to the machine control via a presetter’s built-in postprocessor, so operators don’t have to key in the numbers manually and risk entry errors.

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Zoller’s balancing machines use laser marking, which indicates the position of unbalance and correction with a laser.

Balancing machines measure and compensate for unbalance. The balancer can be used for milling, drilling and other operations, and can range in price from $30,000 to $500,000. “Not all shops require a balancer,” said Drew Strauchen, executive vice president of GWS Tool Group, Tavares, Fla. “Due to price, ROI on a balancer is typically only seen via shops running at higher speeds.” That’s usually higher than 10,000 rpm.

Strauchen continued, “While there are outlier applications where balance certainly helps below these speeds, ROI in applications under this speed are more difficult to quantify. In addition, shops that buy balanced holders that also maintain their balance after repeated tool changes further limit the need for the balancer.”

There are other reasons why a shop may take a pass on buying a balancer. “Some shops may not use tool balancers because their applications don’t necessarily require them,” said Wes Hostetler II, design development team operations manager for toolmaker Allied Machine & Engineering Corp., Dover, Ohio. “Their tooling may be large and rigid, or their tolerances don’t require the precision that a balanced tool allows,” he added. “Depending on the tool balancer options available to their facility, shops may not be able to justify that type of capital investment.”

One question is whether there are longer-term benefits to tool balancers beyond the immediate cost. “Machine shops should assess the requirements of their customers to determine if they should invest in balanced tool systems and tool balancers,” said Axel Wagner, business development manager for toolmaker Wohlhaupter GmbH, Frickenhausen, Germany, an Allied subsidiary. “They should consider current customer requirements and production levels as well as future growth strategies to justify capital investments in tooling and tool balancers.”

Others state that quality must be considered as part of the ROI. “Balancing the entire tool assembly can improve your machining operations in several ways,” said Zoller’s Brothers. “First, by balancing the entire assembly, you can make a more precise part with a better surface finish because vibrations in the assembly will be eliminated. When the vibration is eliminated, you will also see improved tool life and a more consistent production. Additionally, balancing the entire assembly will reduce wear and tear on the machining spindle, which will extend its life.”

Haimer’s Holden makes a similar point. Without balancing, he said, tool tolerances will be affected. “You will cut an oval-shaped hole rather than a round hole in a boring head application, for example.” With balancers, he said, “You can make your parts quicker and more accurately than you’re currently making them.”

The executive added that balancers have enabled some jobs to boost machining speed. “One of our best success stories” involved “a guy running at 300 rpm who can now run at 1,200 rpm with the appropriate increases in feed rate.” At the same time, Holden said balancers can provide peace of mind.

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Haimer’s balancing machines measure unbalance on one and two planes.

“Having a balancer in your facility is a way to confirm that your process is reliable” if problems arise, he said. “We always preach it’s about consistency. If you want a consistent running tool in your production, you need to check the balance of the tooling assembly off the list. If shops want consistency, they have to confirm their settings are balanced every time.”

Allied Machine’s Hostetler described some of the considerations for shops beyond the price of balancers. “The manufacturer has to look at his or her situation and weigh the cost vs. the benefits,” he said. “If the toolholder isn’t spinning, like in many lathe operations, balancing may not be necessary. Depending on what the toolholder is assembled from, a prebalanced toolholder is a good start but not as good as balancing the entire assembly.”

For instance, a toolholder assembly that includes a short 3/16" (4.76-mm) drill would most likely not need balancing compared to a toolholder assembly with a long 1.5" (38.1-mm) drill. In many situations, a balanced tool will outperform an unbalanced tool. “A manufacturing engineer needs to approach each application logically,” said Hostetler. “Many times, they’ll need to perform tests to determine if the cost justifies the end results, with cost being both capital investment and time. End results to consider are quality, tool performance and tool life.”

To Balance or Not to Balance

When does it make sense to balance? There isn’t much question when it comes to high-speed operations. “This is something people can understand,” said Haimer’s Holden. “It is important for high-speed operations. As you rotate a tool, especially an unbalanced tool, you’re going to see an effect on cutting oversize. Your half-inch tool is cutting larger than a half-inch due to the runout caused by vibration due to unbalance and you will probably have to reduce your speeds and feeds. In high-speed machines, the spindle bearings are closer to the working area.” Any adverse effect of unbalance will result in more force being applied to the spindle, which leads to premature spindle failure.

“It becomes very obvious at high speeds,” he added. “Imagine you went out and bought a Ferrari. Driving on the highway, everything is fine up to 65-70 mph, but when at 80 (mph), the car is really shaking, rattling, rolling. You go back to the car dealer and he says, ‘then just drive the car at 60 mph.’ You would think that the car dealer is crazy and you would be quite upset.” That is what is happening in the machining world, as shops are buying high-speed machine tools, or “Ferraris,” that have the capability of going fast but their owners need to slow them down to make good parts. As a result, “They highly underutilize the capability of the machine tool,” Holden said.

“High-speed machining can increase the usefulness of tool balancing in much the same way that balancing the entire toolholder assembly can improve machining,” said Brothers of Zoller. “By machining at high speeds, you can make more precise parts, with a better surface finish, which provides you a more consistent production process.”

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A GWS Tool Group reaming tool. The company says that tool balancing improves performance when a tool is run at higher speeds by ensuring proper hole tolerance and finish, as in this example of a single-fluted, self-locating reamer, which is non-symmetrical by design.

There are other considerations when using balancers. “It really comes down to each facility’s individual machining process and how they want to balance,” Brothers said. “For instance, you can balance in one or two planes (top and bottom). You can add weights to a toolholder if it’s a multi-use holder for other types of tooling. Or, if it’s a dedicated holder, you could remove material by milling or drilling the matter out.”

Zoller says its toolBalancer product can help users by going through each step of the process, including how much weight to add, where to place it or where to remove it.

Shops “will need options for balancing short tools, long tools and grinding wheels,” Brothers said. The Zoller toolBalancer, he added, “can handle the various types of balancing needed for these differing tool types.”

Balancing is a good best practice to institute in any shop, according to Strauchen of GWS Tool Group. “Having one enables manufacturers to learn which applications and tool types are frequent offenders that need balancing (boring bars for example), so as to learn over time which applications they should be balancing and which are likely good to go,” he said. “For example, a shrink-fit holder with a small-diameter tool in an HSK-type holder is likely going to be perfect out of the gate.”

Strauchen outlined examples of how balancing can vary. “The size and relative options typically correlate to the shop’s level of production output,” he said. “Very long tools (over 6" [152.4-mm] long) may require a balancing machine with two-plane balancing, using balancers with taller hoods to contain the entire assembly. Grind shops using wheel packs, which are shorter, will generally need standard balancing options with short hoods and single-plane balancing. When it comes to the tool in the spindle, we recommend balancing the entire assembly…to a balance spec of G 2.5 at a speed equal to the fastest spindle in their shop.”

In this way, “balance is good regardless of what machine they run our tool in,” Strauchen added. “Because we make a lot of custom tools, including boring tools and form tools, balance often plays a role as the nature of design can often create a non-symmetrical cutting tool that needs to have a balance correction. While we make balance corrections on the tool itself, best practice is still to do so with the entire assembly together to ensure proper performance.”

The Tool Dynamic TD Comfort Plus offers an optimized touchscreen, integrated PC, and storage for balancing accessories and equipment.

Once you choose a system, you should stick with it, according to Holden of Haimer USA. “You want to make sure the balancing system can clamp the tooling assemblies correctly in order to measure accurately and then give you easy-to-follow instructions on where and how to correct the unbalance,” he said. “Choose one that you know will be accurate and guide you to the results you want—a truly balanced tooling assembly.”

How to Choose the Right System

Every tool balancing system has pros and cons, according to Hostetler of Allied Machine. “Some systems are overkill for certain machining applications and others may not have enough options to achieve the performance required,” he said. “Ultimately, you need a tool balancer that works best with the types of operations you perform. An engineer can help determine their shop’s requirements and assist in sourcing the best economic solution available.”

Some of that may depend on the shop’s customer base. “If a shop has customers from aerospace or automotive, they look for high-precision tools and will invest more to meet their customers’ requirements,” said Wagner of Wohlhaupter. “To achieve the best process, they need to have well-balanced tools. These shops will have applications where every tool gets balanced before they put it in the machine.”

Also, the type of tool comes into play when selecting balancing options. “Short tools and small grinding wheels have limited options, but assuming there isn’t as much weight to these type of tools, there should be less manipulation required to balance them,” Hostetler said. “In my applications with small grinding wheels, I’ve learned that I need to establish the wheel to the machine before balancing it. When establishing the wheel, I’m not running at high speeds, I’m merely stabilizing the wheel to the truing roll and removing as many imperfections as possible. I can then balance the entire assembly with minor adjustments to get the best performance.”

Hostetler said it’s important to consider the steps needed to balance a tool. “I suggest finding a balancer that is able to give a reading in two to three process steps. When it comes to the physical action of balancing, there are many options out there. I use radial drilling, axial drilling and weighted set screws. Besides drilling, shops could also be milling or grinding. Instead of weighted set screws, they could utilize weighted rings. What’s nice is that many of these options can be tailored to their shop, giving them the freedom to pick and choose what is best for their business.”

Wagner added that tool size and machining speed are the key issues. “The larger the tool, the more important it is to get the tool balanced by dynamic balancing, rather [than doing] that statically. Small grinding wheels mean higher rpm. As the rpm increases it becomes more important to assure your tools are balanced.”

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