How to Choose the Best Toolholding System for Your Shop
Article From: April 2020 Manufacturing Engineering, Bill Koenig, Senior Editor
Stay with the tried and true? Or go with something new?
Many job shops hold onto traditional, inexpensive tooling systems. ER collets and Weldon flats are tried and true; they work and are proven. At the same time, newer, advanced machining technology, such as multi-axis machines, may perform better when newer, advanced (and more expensive) toolholders are deployed.
As a result, job shops face more choices and more analysis is needed.
“Two of the main criteria for judging the quality of a toolholding system are runout and repeatability,” said Luke Pollock, product manager for Walter USA LLC, Waukesha, Wis. “From this perspective, shrink-fit and hydraulic holders belong in the ‘best’ category. They both securely make contact with a precisely ground cylindrical shank and offer minimum runout and maximum repeatability. ER collet systems are probably in the ‘better’ category. Reasonable runout and repeatability can be achieved with this type of holder. The runout and repeatability can be improved by using precision-ground collets. Weldon shank holders offer the least amount of runout control since the system uses a set screw to push the shank to one side of the toolholder bore, so it inherently introduces some runout into the tool setup.”
Pollock said clamping strength is another consideration. “Making a decision from this perspective changes which holders we consider ‘best,’” he said. “A Weldon shank toolholder uses a connection that makes it impossible for the tool to slip or pull out. Therefore, with this toolholder, we can push the machining application extremely hard, to the limits of the application. Shrink-fit and hydraulic holders also offer very good clamping strength. However, in certain circumstances that may include high material removal rates or a large contact between the tool and material to be machined, and it is possible for some slip or pullout to occur.”
Much depends on what applications are involved. Drew Strauchen, executive vice president for GWS Tool Group, Tavares, Fla., said that “generally speaking” the good category includes end mill holders and collets; better includes high-precision collet chucks and mill chucks; and the best includes shrink-fit, hydraulic, and press-fit.
“The core fundamentals of a great holder are rigidity, gripping strength, runout accuracy and balance,” he said. “As applications range from roughing to finishing, low production to high production, and low to high tolerance, the importance of the holder and its individual attributes become more or less critical.”
Controlling Runout Key to Tool Life, Accuracy
Edwin Tonne, training and service technical specialist for Horn USA Inc., Franklin, Tenn., cited examples of applications for different categories.
Hydraulic holders, he said, are best for drilling applications, high-speed finishing and reaming. Shrink-fit is best suited for rough milling, finish milling, drilling and reaming; and high-performance collet systems are also good for rough milling, finish milling, drilling and reaming.
Tonne also described the considerations when selecting toolholding options. For drilling or reaming tools, he said, runout “is key to economic tool life and dimensional accuracy.” With rough milling, runout also is critical “as well as shank gripping force. Since the torque demand on the toolholder is higher, the risk for pullout is greater.”
Said Walter’s Pollock, “It is important to match the correct type of toolholder to the application. A better way to look at it is to consider which feature of the toolholder is most important to the application. Rough applications will benefit mostly from a toolholder with the highest clamping strength. In finishing operations, where precise tolerances and fine surface finishes are the goal, toolholders with minimum runout and maximum repeatability should be the first choice.”
The equation for job shops may vary. Dan Doiron, product manager-milling for Emuge Corp., West Boylston, Mass., described the considerations when selecting toolholding options for different types of cutting tools.
“When I see a tool with a Weldon flat, that usually signals that this tool is designed for aggressive milling,” he said. “That’s not to say you couldn’t use the tool for finishing, but the Weldon flat was added to the tool to prevent pullout. For roughing, the pin-lock collet is a good choice. For machining of 3D surfaces of a mold core or cavity, an Emuge FPC brand toolholder will deliver a high level of accuracy out of the box. With the balanceable holder, accuracy is increased without having to purchase a separate holder.”
Toolholding Often Overlooked
For job shops, the question now is how to proceed. For example, when should job shops opt to invest resources and move forward?
“Toolholding is often overlooked, especially when a new machine is purchased,” Doiron said. “However, shops should consider upgrading their toolholding strategy if the machine was purchased to increase production and to perform at a higher accuracy standard. For example, using the old side-lock holders and expecting the performance level to improve will end up being disappointing. The holder is still inaccurate regardless if it is in an old machine or a new machine spindle.”
Some considerations depend on the size of job shops. “The biggest balancing act is between flexibility and performance,” said Alan Miller, engineering manager and product manager for BIG Kaiser Precision Tooling Inc., Hoffman Estates, Illinois. “The more flexibility a system has, the less performance that it’s probably going to offer for specific applications. In high-production environments, you want to focus on the best performing solution. Where we get into the very small job range, having the flexibility of the toolholder system may trump getting the ultimate performance out of the cutting tools.”
When it comes to investing in newer technology, “It’s easier to do with larger shops,” he said. “It’s harder for a very small shop to give up flexibility.”
Regardless, job shops are examining whether investing in newer technology is worth the cost in reduced scrap and longer tool life.
Big Benefit for Holemaking
“The core fundamentals of a great holder are rigidity, gripping strength, runout accuracy and balance,” GWS’ Strauchen said. “Holemaking tools benefit in particular from holders with higher degrees of runout accuracy and balance. End mills benefit from the same but generally need holders with additional rigidity and gripping strength to better manage radial loads and pullout forces created via helical end mills. Sometimes, pullout forces are such that a mechanical fit system like a side-lock or safe-lock system is needed.”
Executives say any time a shop is investing in new tooling, toolholding should be evaluated. “If a shop is investing in new machining centers, it is important to also complete the purchase with new toolholding,” said Horn USA’s Tonne. “It does not make economic sense to gain productivity advantages from, say, a faster chip-to-chip time if it is squandered on tool changing due to poor tool life.”
Strauchen expressed a similar view. When asked when a shop should consider upgrading toolholding, he replied: “Aside from the obvious answer of ‘always,’ a more realistic answer is when they purchase a new machine tool. Aside from the machining applications themselves and performance, higher quality toolholding systems generally have better balance properties and maintain better fit—more accurate V-flange tapers, for example—that will maximize the life of the spindle. You wouldn’t put your old car rims on your new car, nor should you put used holders in a brand-new spindle.”
One part of the evaluation is in the effect a new toolholding system will have on new tools. Improved tool life is a major reason to make a change.
“Probably the easiest place to see an ROI from improving the quality of the toolholding system is the performance of the tool,” Walter’s Pollock said. “Tool life is something most of us are able to monitor. Getting more tool life from a single tool means more parts from the same production cost. This means a lower cost per part is achieved.”
Also, he said, higher production rates may be achieved. “When accounting for the burden rate of the machine and operator, shorter cycle times have much more impact on lowering the cost per part,” Pollock said. “The overall cost per part is a pretty solid way to calculate the benefit of an improved toolholder.”
Big Tool Life Gains are Possible
“The biggest return on investment when purchasing the latest and best toolholding systems will be in the increased tool life, hands down,” said Emuge’s Doiron. “For example, it has been reported to us by an end user that tool life increased five times by simply changing over to the Emuge FPC toolholder. Their initial challenge was the tool life they were experiencing was unacceptable. Their part setup was not optimal because the nature of the application and part configuration didn’t allow for many workholding options. Without changing any speeds and feeds they were currently running, they immediately could tell the difference in performance once the FPC was implemented into the [machining process].”
Ultimately, it’s up to shops to see for themselves when deciding whether to upgrade. “Test it,” said Strauchen of GWS. “Quantifiable data points one can gather include” tool life, such as number of parts and number of minutes; cycle time; part surface finishing; and toolholder life, he said. “Most toolholder manufacturers, especially high-end ones, will work with customers to help prove out their technology.”
Added Tonne of Horn USA: “The best way is to run internal trials with all the prospective holder types. Find a job with known tool life data and enough volume to run the trial with all the options. Tool life is a main criteria but not the only one. Also, bring in a good cross section of the shop talent, from the newer machinist to the veterans. Have each assemble the tools and note any potential difficulties. During the testing, keep everything ‘apples to apples.’ Use the same machine, component, coolant, and program. Make measurements at regular intervals. This will ensure that tool life is under control and valuable components are not at risk.”
While tool life is critical, Tonne advised shops to take a wider view. “Don’t focus only on tool life,” he said. “Look at the burrs created, surface finish, [how the tool] sounds and try to use as much quantitative data as possible.”