Not even the suppliers of best quality ER collets will provide a guarantee, of specified parameters, for anything but the nominal size &#; certainly not the minimum achievable.
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Hobbyists are not generally absolute perfectionists to absolute sizes &#; as may be required for series production of replacement parts for high precision machines. I use ER &#; and also a Clarkson occasionally.
Maybe viewing some of those REGO-FIX videos first would have turned up the information that less than nominal sized tool shanks, or in our case when there being used as a work holding collet, they show no increased run out, and they will in fact guarantee those same guaranteed run out numbers over the holding range of the collet. At least REGO-FIX does. If an ER collet and it's chuck are correctly and accurately made, the collets segments will close down evenly against the tool shank, in fact there designed to do exactly that and provide the high grip strength ER collets are known for. So why would smaller than optimal diameters be any different than on size diameters since the collet has to close at least a bit even with on size tool shanks? My Bison ER 40's show no increase in run out over the various sizes I've checked. When I want holes with a high degree of location accuracy, or I'm using large diameter reduced shank drills, I'll use them instead of a drill chuck, so I can also use mine as a tool holder with a variety of sizes within each collets closing range. That ability is simply due to the radial and axial precision the collets and chucks are being made to, and what I think can be assumed adds a high percentage to the actual cost for those better collets and chucks. There's also more than a few YouTube videos that show cheap off shore ER collets having visually noticeable differences in segment widths, differences in slot widths, burrs etc. Since the collet isn't and can't close evenly around it's full circumference, then of course it will produce higher run out numbers even "if" it was bored and ground true to it's tapers. And if there being made that poorly, then it's highly doubtful anything else is correct other than by pure luck. There's also videos showing collet chuck thread deviations and nuts with internal tapers that are out of square enough to force the collet sideways or physically tilt the collet axially as the nut is tightened. So it's not only the concentricity of the collets themselves, it also has a lot to do with just how accurate the collet blocks or chucks are as well.
5C is completely different because of how there designed to work. That design of collet isn't meant to accept anything over sized, and even a bit too far under size will or can crack or break collet segments if the collet is closed on any smaller than optimal diameters. Since a 5C collet is a single taper and closed by drawing the collet inwards against the collet holders taper, that forces the collet segments to exert the most holding power towards the front of the collet. For that reason, special soft 5C over sized collets can be machined and used even for very short parts. If 5C was being used for driving tools, then yes nominal sized collets to fit the tool shanks diameter would be logical to obtain the highest grip. Possibly there still being made somewhere, or at least were at one time. But other than those now fairly rare machine tools that were designed to use 5C, I can't recall seeing any actual 5C milling chucks. About the only option left would be to build your own if that's what you really wanted to use. As a tool holder, I think 5C is a rather poor second choice.
ER collets are a dual taper, and the segments at each end are forced in and closed by both the chuck and closing nut tapers as it's tightened to the correct torque. For that reason it's highly recommended that at least 80% (or more) of tool shank, or work piece fills the collet length. If that's not done, then the collet's grip is seriously decreased and a collet can be permanently damaged because the tool or part is then only being gripped by the front of the collet. Run out numbers will then increase, but that's the fault of the user because there being used improperly and outside there intended design application.
It's also not about being a perfectionist, and as I already said, those REGO-FIX videos clearly explain just how detrimental any excess run out is to maximum tool life no matter what collet type or tool holding method is used. And since the ER collet design has a decent amount of closing range when holding work pieces, you can be quite sloppy about those exact sizes as long as the part length is inserted deep enough into the collet. 5C collets would require much more attention to those nominal diameters than ER's ever would. Like anything else, there's no perfect one size fits all when it comes to tool and work holding collets. 5C is logically the clear winner as a work holder just due to it's versatility. ER is a much better and far more secure tool holding method because of it's grip ability over the length of a tool shank.
Collets are among the most commonly found items in machine shops. However, even professionals who routinely use these toolholding mainstays may not know all the critical details about them.
This article dives into the intricacies of collets &#; from their design and types to how they compare with other toolholding options. It also covers the latest advancements in collet technology and provides tips for choosing and using collets to extend their lifespan and improve machining results.
Placed in a chuck, a collet forms a collar around the tool or workpiece. The ER collet, the most widely used tool-clamping option, exerts clamping force through compression when tightened with a nut. ER collets are commonly used to hold tools like endmills, drills, taps, and reamers.
Shrink-fit holders are designed for precision but come with limitations:
In contrast, ER collets are more versatile, as one holder can accommodate a variety of tool shank sizes.
Hydraulic and milling chucks allow for straight reduction collets to adjust tool sizes. However, their performance is reduced compared to ER collets due to increased runout and decreased clamping force.
Contact us to discuss your requirements of Collet Material. Our experienced sales team can help you identify the options that best suit your needs.
Alan Miller, engineering manager at BIG KAISER Precision Tooling Inc., explained that the main advantage of ER collets is their versatility. For example, an ER32 collet chuck can hold tool shanks ranging from 3.175 mm (0.125") to 19.05 mm (0.75") by simply swapping out collets.
Held by a collet, a thread mill cuts threads. Image courtesy of Guhring.ER collets offer compression flexibility but have limitations. Andy Moon, product manager for milling and toolholders at Guhring Inc., noted that this flexibility is limited to a small range &#; typically between 0.5 mm (0.02") and 1 mm.
ER collets are not ideal for high-torque cutting. Their compressibility, which provides flexibility, also introduces runout and instability, making them less suitable for heavy-duty machining.
&#;For high-performance applications, especially in milling, I generally steer people away from an ER collet chuck,&#; Moon said.
However, for light milling or finishing tasks, ER collets remain an excellent choice. Matching collet size to the tool shank diameter is critical for optimal performance.
Emuge Corp.&#;s FPC collets are designed for precision with minimal flexibility. They conform to ISO H6-H9 standards and fit one specific tool diameter. The newly introduced Slim Line models address challenges in confined workspaces, especially for five-axis machining.
FPC Slim Line collet chucks are ideal for confined work areas. Image courtesy of Emuge.BIG KAISER Precision Tooling introduced Perfect Seal and Perfect Jet collets for hydraulic chucks:
Proper maintenance can significantly extend the life of collets and improve machining results. Here are some do&#;s and don&#;ts:
Collets are used for securely holding tools or workpieces in machining tasks, such as milling, drilling, and reaming.
Types include ER collets, FPC collets, shrink-fit holders, and hydraulic chucks, each with unique strengths and applications.
Base your choice on tool size, required clamping force, and machining application. ER collets are versatile, while hydraulic and shrink-fit chucks are better for precision work.
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