Chucks are used to hold round shank tools. There are many styles of chucks, and chuck selection varies depending on:
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In the table below, you can see a comparison between different styles of chucks, which can help you to make the best chuck selection.
High-precision hydraulic chuckShrink fitPower chuckER collet chuckWeldon Pull-outThe cylindrical shank is clamped evenly and is used for the best run-out accuracy for milling, drilling and reaming. With no flat or locking, it has torque and axial force limits before the shank moves in the holder.
The hydraulic membrane provides high clamping force and run-out accuracy. It is very simple to handle, without the need for separate equipment. Collets can be used, which reduces the number of chucks needed and allows coolant to be delivered through the tool (drilling) or through the collets (milling).
The bore of the chuck is slightly smaller than the shank diameter; the chuck is heated up to expand when changing the tool. Due to thermal expansion between the holder and the tool shank, shrink fit chucks are mainly used for solid carbide round tools. Heating equipment is needed to change tools and each chuck is for one shank diameter and coolant delivery only. This makes shrink fit best suited for production with a tool-setting room for tool changing.
Shrink fit offers good accessibility and high run-out precision, with medium to high clamping force.
The run-out accuracy and clamping force are not as good as with hydraulic or shrink fit chucks. However, the very good flexibility with collets makes the ER collet chuck an economic all-round chuck for drilling and light milling applications. The tool change can be handled at the machine with a fixture. Use a torque wrench to ensure that the chuck is not overtightened, which reduces accuracy and damages the chuck.
A shank with a flat is used for higher torque applications where torque security is more critical than run-out accuracy.
The drill adapter is suited for medium to large drilling operations. The flat runs all along the shank, as the drill has only compressive axial forces (pull-out is not a risk), but has an axial face contact with the adapter for best stability. The drill adapter differs from the Weldon adapter, in that the face of the adapter is ground and the shank is longer for best stability.
The Weldon or “milling” adapter was the traditional chuck used for milling applications. The short flats provide torque resistance and pull-out security. However, the downside with Weldon is the run-out accuracy, which is an important factor for milling tool performance. More often, this type of chuck is replaced with shrink fit or hydraulic.
The modular screw coupling interface provides many benefits for milling and boring. For smaller machines, removing the need for a chuck allows for shorter gauge lengths, which dramatically reduces vibration. For long overhangs, the shank material and shape can be optimized more easily compared to solid tools.
For milling, longer solid carbide tools are costly; when only the end is used, tool costs can be significantly reduced.
Used mainly for small and medium machine spindles (HSK40/50/63 – steep taper #30, 40 – C3/C4/C5/C6). All other chucks build length into the assembly. Reduce the gauge length to below three times the flange contact to reduce vibration and increase productivity.
The shank length is selected that provides the best stick-out length from the chuck. Steel is used up to 3 x D and solid carbide up to 8 x D.
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The conical shape has a big impact on stability. Conical should always be used where clearance allows and for 5-axis machining. Replacing conical solid carbide end mills has a big impact on tooling costs. Conical shanks exist in cylindrical shanks as well as Coromant Capto® for steel.
Over three times the shank diameter, vibration is always an issue. Optimizing the stick-out length to the absolute minimum required makes a difference. The G undersized shanks are 0.3 mm (0.012 inch) smaller than the cutting diameter and used in combination with dedicated collets for hydraulic chucks, the shank length can easily be modified. Their application area is from 3-6 times the shank diameter.
The tap adapters are designed for tapping operations in machines equipped with automatic tool change. A construction for pull and pressure compensates for differences between spindle feed and thread pitch. Even micro differences between calculated feed and actual pitch of the tap can lead to extremely high thrust forces on the tap flanges and an increase in cutting pressure. When threading with a tap with a cylindrical square shank, it is important to use a tap adapter of the same size as the shank/square.
Synchronized tapping chucks, such as CoroChuck® 970, are based on a micro compensator, which aligns radial and axial deviations. Thrust forces are reduced on the tap flanks, which results in better surface quality and longer tool life. Synchronized tapping chucks use ER collets with a square drive. It is not recommended to use a collet without the square drive, due to the high torque that will make the tap rotate in the collet if the square drive is not used.
For quick change tap adapters, it is also important to use the right-sized tap adapter; otherwise, the risk of tap breakage is high and tolerance on the finished thread is poor.
To get the best result from machines that are not equipped for synchronized tapping, the following recommendations should be observed:
Instead of relying on a nut, collet or extreme temperature to clamp the body of a tool, hydraulic chucks use fluid. By compressing an internal membrane in the holder body, the hydraulic fluid applies uniform pressure around the cutting tool. This fundamental design feature brings us to the first asset hydraulic chucks bring to the table: concentricity. The evenly applied gripping provides more control and consistency than a collet or manual tightening of a nut.
Concentricity is especially valuable in high-speed machining applications where depth of cut is relatively shallow. Preventing even one of a cutter’s teeth from taking more of a load will extend tool life and reduce costs. Standard hydraulic holders offer exceptional runout, while our Ultra Precision Type measures staggering runout accuracy of one micron at 4xD. It stands to reason that hydraulic holders were originally designed for high-performance drilling/reaming applications and lighter milling.
Aside from stellar cutting performance and precision, hydraulic chucks offer setup flexibility. When assembling a tool, one of the best principles to follow is to make every tooling assembly as short as possible. The shorter the tooling, the less room for error. It also makes for easier access to tricky pockets when advanced workholding or extra axes aren’t an option.
Compared to more general-purpose holders, hydraulic chucks have a smaller nose diameter relative to the tools they hold. This is critical, as these holders allow a further reach into mold cavities or other tricky work envelopes with less interference and without using extensions that can sacrifice rigidity. These characteristics make hydraulic holders especially effective in delicate 5-axis machining, finishing especially.
Our Super Slim Type, for example, features nose diameters as small as 14 mm (.551"). We’ve been able to design the hydraulic system with a very tight tolerancing of the bore, allowing for clamping down to three millimeters and spindle speeds up to 45,000 RPM. Meanwhile, the natural damping characteristics of the hydraulics are especially advantageous in these extreme scenarios as well.
There’s also the option to have coolant delivery directly to the cut with hydraulic holders. Ideal for smooth, stable finishing operations our Jet-through Type allows for conversion between jet-through and center-through delivery for an improved surface finish and tool life.
Setups aren’t only flexible, they’re also quick and simple. A single hex key wrench is used to clamp or loosen the cutting tool, making it easy to swap cutting tools at the machine or offline without the need for any special equipment.
Ultimately, hydraulic chucks will cost you a little more. But as the old adage goes, you get what you pay for. Shrink-fit holders boast similar performance and cost less up front, but that doesn’t factor in the cost of heating/cooling equipment and time. ER collets or side lock end mills may remove a lot of material, but if any precision or consistency is required, hydraulic chucks are the better option. Plus, their simple handling and relatively low maintenance make life easy on machinists.
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