Spindles and tool holders are in a constant battle with the forces of nature, with this battle becoming more and more difficult with heavier cuts and longer projections. Chattering and deflection have always been the bane of machinists’ existence, so much so that the sight of a long and slender toolholder will immediately cause goosebumps. If you understand why a long tool holder behaves the way it does, you’ll know that there are ways to fight back against this bending. Every machinist knows that short and stubby holders are more resistant to deflection than long and slender holders. You’ve also probably heard that, if possible, you’ll want most of your cutting forces to be axial rather than radial. Not only does this fight chatter in operations like boring, but your spindle also is better equipped to handle loads in this axis. However, these options aren’t always going to be on the table, especially in unavoidable longreach situations and many milling operations. In this constant battle with tool deflection, much time and effort has been spent designing shorter holders, stiffer tools, and clever antivibration geometry and materials. But oftentimes, the body diameter(s) of the holder can be overlooked as a means of increasing rigidity, especially in situations where it is all you have to work with. This is a serious shame, as you’ll soon discover. The concept of dualcontact technology has been around for years, existing in many different forms but always with the same goal of capitalizing on this untapped potential of rigidity. For those who don’t know, dual contact refers to the shank contacting the spindle taper and the spindle face simultaneously. Oftentimes, the solution involved ex post facto alterations to the spindle or tool holder, such as using ground spacers or shims to close the gap, for example. In other words, there was no standard solution, and if you wanted dual contact, you would have to be prepared to spend time and money either buying modified tool holders or modifying them yourself to adapt them to your spindle. BIGPLUS emerged as a solution to this issue. Essentially, both the spindle and tool holder were ground to precise specifications so that they closed the gap between spindle face and flange in unison (while depending on very small elastic deformation in the spindle). What this meant is that operators were able to confidently switch BIGPLUS tooling in and out of a BIGPLUS spindle and achieve guaranteed dual contact. Not only that, but standard tooling could still be used in a BIGPLUS spindle if necessary, and vice versa. Though not technically an international standard, it’s been adopted by many machine tool builders because of the clear performance improvements and simplicity. In fact, BIGPLUS spindles come standard on more machines than you would think. We often come across operators that have machines with BIGPLUS spindles and don’t even realize it. How exactly does dual contact help with tool rigidity? The torque (or moment) exerted by the cutting forces is maximized at the point where the holder and spindle meet, the base of the tool holder. With standard CAT40 tool holders, this would be the gage line diameter. When the holder contacts the spindle face via BIGPLUS, the effective diameter would be the larger diameter of the vflange, since this is the new anchoring point of the holder and spindle. So, you are beefing up the diameter at the point where the reactionary force is greatest. It’s not too much of a leap to conclude that a larger effective diameter will give you more rigidity. That being said, you may still be asking yourself: does such a seemingly small increase in diameter really make a difference? To understand the effect of BIGPLUS, you must understand the physics behind it. Imagine a simple scenario in which a tool holder is represented by a cylindrical bar that is fixed at one end and freefloating at the other. In other words, a cantilever beam. If you think about it, this is essentially what a tool holder becomes once it’s secure in the spindle. Now, let’s introduce a radial force F that acts downward at the suspended end of the bar, which represents a cutting force you would encounter when milling or boring, for example. The bar, as you might expect, will want to bend downward. It’s similar to how a diving board bends when someone stands at the end, though less exaggerated. It’s possible to predict the amount of deflection (or inversely, bending stiffness) at the end of this hypothetical bar if you know its length, diameter and material. The expression below represents the stiffness k at the end of the bar where d=diameter, L=Length and E=Modulus of Elasticity I won’t ask you to do any math here, I just want you to look at the equation. We can see that increasing d will increase the value of k, while increasing L will decrease the value of k, since it’s in the denominator of the equation. This certainly makes sense if you think about it: a short and squat bar (large d, small L) will be more rigid than a long and slender bar (small d, large L). Something interesting to note is that d is raised to the 4th power, while L is only raised to the 3rd power. Diameter affects rigidity an entire order of magnitude more than the length does. This is where the power of BIGPLUS comes from and is why a small increase in diameter can have such a powerful effect on performance. For a CAT40 tool holder, the gage line diameter is Ø44.45 mm and the flange diameter is Ø63.5 mm. Let’s imagine two bars of identical length and material, so L and E remain unchanged. One bar has a diameter of Ø44.45 mm (standard CAT40) and the other has Ø63.5 mm (BIGPLUS CAT40). If you were to plug these values into the above equation for comparison, you would find that the BIGPLUS holder results in a k value that is around 4 times greater than the standard bar. Based on this comparison, you could say that a BIGPLUS holder is 4 times as rigid as an identical standard CAT40 holder, because it is 4 times as resistant to deflection. Think of the tool life and surface finish improvements you would see with a tool that is 4 times more rigid, not to mention the reduction in fretting and potential for reduced cycle time. You would get similar results if you were to make the same comparison for CAT50, BT40, BT30, etc. If you’re still not convinced, we can also compare the rigidity in this way: Let’s say there is a Ø63.5 mm BIGPLUS CAT40 bar of some arbitrary length. One of our more common gage lengths is 105 mm, or just over 4 inches, so let’s use it as an example. You’re probably wondering, at what length would a comparable standard CAT40 holder have an equal stiffness? If we take our stiffness expression and set it equal to itself (one side representing BIGPLUS, the other non BIGPLUS), we can plug in this BIGPLUS holder length and our known diameters to find our unknown nonBIG PLUS length: What does this mean? A BIGPLUS holder of around 4 inches or 105 mm in length will have equal rigidity to a standard CAT40 holder of around 2.5 inches or 65 mm in length. Any experienced machinist will know quite well the difference in rigidity between a 4inch long holder and a 2.5inch long holder.
If this is true, we can say that implementing BIGPLUS is equivalent to a 40% reduction in length in terms of rigidity. Theoretically, a BIGPLUS tool holder will behave like a standard tool holder that is nearly half of its length! Obviously, we’ve used simple and idealized cases here to represent the complicated and dynamic world of metal cutting. Tool holders, of course, don’t have uniform body diameters or materials and the cutting forces usually aren’t acting in one direction in a constant and predictable way. If our holder necks up and down to different body diameters along its length, which is realistically what happens, each of these sections would be its own microcosm of “beam” that would influence the overall behavior (at that point, finite element analysis on a computer becomes the only practical way to predict behavior). So, will the advantage of BIGPLUS really be as dramatic as our handcalculated classical beam theory suggests? Probably not, but it depends on the tool holder/tool. Most cases will follow our simple model quite closely in practice; others not so much. If nothing else, we’ve demonstrated how dramatically the flange contact of BIGPLUS can influence rigidity, at least in a purely mathematical sense. As if you needed any more reasons to be on the BIGPLUS bandwagon besides increased rigidity, you will also eliminate Zaxis movement at high speeds, improve ATC repeatability and decrease fretting. This means that you will take heavier cuts, scrap less parts, and increase tool and spindle life. BIGPLUS isn’t a new idea by any means, but with a proven track record of tackling tough jobs, it’s hard to imagine working in a modern machine shop and not taking advantage of what it has to offer. If you’re still not convinced, we can also compare the rigidity in this way: Let’s say there is a Ø63.5 mm BIGPLUS CAT40 bar of some arbitrary length. One of our more common gage lengths is 105 mm, or just over 4 inches, so let’s use it as an example. You’re probably wondering, at what length would a comparable standard CAT40 holder have an equal stiffness? If we take our stiffness expression and set it equal to itself (one side representing BIGPLUS, the other non BIGPLUS), we can plug in this BIGPLUS holder length and our known diameters to find our unknown nonBIG PLUS length:
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Technical Support BlogAt Next Generation Tool we often run into many of the same technical questions from different customers. This section should answer many of your most common questions.
We set up this special blog for the most commonly asked questions and machinist data tables for your easy reference. If you've got a question that's not answered here, then just send us a quick note via email or reach one of us on our CONTACTS page here on the website AuthorshipOur technical section is written by several different people. Sometimes, it's from our team here at Next Generation Tooling & at other times it's by one of the innovative manufacturer's we represent in California and Nevada. Archives
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