Chuck
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A chuck is a device that takes on tools such as drills or milling cutters ( drill chuck ) or the workpiece to be machined ( lathe chuck or colloquially American ).
Collet chucks and collet chucks
Clamping head chucks usually work according to the pulling principle. The clamping head is coupled into the pulling mechanism by means of a changing device. The clamping cylinder pulls it into the cone of the chuck body via the draw tube. The link between the draw tube and the draw mechanism is the draw tube adapter. It and the spindle flange are each adapted to the specific machine. Clamping head chucks are balanced to a high balance quality and have a stroke limitation in both directions on the chuck side. All clamping jaws of the clamping head have a groove for radial fixation. Clamping head chucks are characterized by a high degree of rigidity, concentricity and ease of conversion.
Drill chuck
Drill chucks often work in such a way that the part to be fixed is clamped between three clamping jaws (three-jaw chuck). This design has the advantage that fixed insert tools (e.g. a drill) can be centered well, which is particularly important in the case of rapidly rotating machines. Inside the chuck there is a screw that pushes the clamping jaws into a cone when they are closed, thereby clamping the tool. Keyless chucks can be opened and closed effortlessly by hand despite the high clamping forces. Key-type drill chucks offer higher clamping forces on hand drills by clamping with a drill chuck key. Machine chucks on milling cutters and boring mills must also be tightened with appropriate tools because of the high torques . As a rule, the holding thread of the drill chuck is 1/2 "x 20 in UNF fine thread design. Drill chucks for masonry drills on rotary hammers do not clamp the tool in an SDS drill chuck by frictional connection , but allow the tool to move axially and transmit the torque by means of Form fit . Drill chucks with adjustable clamping jaws for cylindrical shafts are commercially available up to 16 mm (hand drills 13 mm), smaller dimensions are 10, 6 or 3 mm, each of which also represents inch fractions. On pillar or column drilling machines , the mount is via Morse taper adapter .
For precise holding of fine drills with diameters of 3 mm and smaller, collets with 3 tongues are used in miniature drilling machines - each only for a narrow area. 4-tongue collets are built into the simplest drill bits for small drill bits with a square shaft.
For machine tools, there are holders with hollow shank taper or steep taper for drills, which are designed as whistle notch or weldon . A surface is attached to the drill shaft on which a screw fixes the drill in the receptacle. Furthermore, drills with a cylindrical shaft can be clamped in shrink holders of machine tools.
Lathe chuck
The chuck on lathes or on lathes / turning lathes is called lathe chuck .
They are either supplied directly suitable for the lathe mounting system or attached to the machine by means of a so-called flange, which has the machine mount on one side and the shape of the chuck on the other. For reasons of precision, this chuck side is turned off directly on the lathe on which the chuck is to be used.
The usual chucks clamp round or regularly shaped three- and six-sided workpieces in three jaws (three-jaw chuck), precisely shaped round and square or octagonal workpieces in four jaws (four-jaw chuck). Special shapes also have two or more than four jaws.
When tightened, the jaws move evenly in the direction of the axis of rotation, so that the workpiece is always centered. A distinction is made here between the flat spiral chuck and the wedge bar chuck; With the flat spiral chuck, the jaws are moved by means of the flat spiral turned by the clamping key; The wedge bar chuck developed by the Forkardt company uses wedge bars which clamp the jaws.
The usual basic equipment of a lathe chuck includes a set of drilling and a set of turning jaws; Drill jaws are stepped sloping outwards from the feed center point and thus allow good machining of z. B. Rod material; Turning jaws are stepped sloping from the outside inwards and thus allow z. B. the clamping of larger workpiece diameters.
The clamping jaws are normally made of hardened steel, but better concentricity is achieved with soft clamping jaws, since the play in the guides can be compensated by turning the clamping jaws out. In addition, there are also special so-called split jaws that have a base body that is supported by the z. B. flat spiral is moved, and have screw-on soft jaws.
In some special lathe chucks, flyweights are located in the chuck body in order to counteract the centrifugal forces of the clamping jaws in high-speed lathes, which press the jaws against the workpiece via levers.
Manually operated chucks are mostly used in conventional lathes , but also in z. B. dividing apparatus used. They must be opened or closed with a chuck key. Hydraulic chucks (power chucks) are mostly used on CNC machines . They are operated manually by a pedal or, in the case of automatic loading, by the control system (example: bar material is automatically pulled out of the chuck with the bar gripper ).
Special forms of the lathe chuck:
- the so-called faceplate : it has (mostly four) separately adjustable jaws, which enable the clamping of parts with an asymmetrical clamping surface, e.g. B. a crankshaft.
- the clamping disc: it consists of a flat disc and has no jaws; Special parts are attached to it by screwing or with the help of clamping claws and rotated.
- The Wescott chuck: It combines a flat spiral chuck and a faceplate, the jaws can be adjusted separately as with the faceplate, but the adjusted jaws open and close together as with the plane spiral chuck.
Both the face plate and the clamping plate are only operated at lower speeds due to the imbalances that occur.
Other clamping means on the lathe: two-jaw chuck , clamping between centers , rotary mandrels and mandrels , hydraulic expansion , collet , bezel (steady rest).
Shrink chucks
One of the most precise clamping methods on milling machines in terms of concentricity is offered by clamping with a shrink-fit chuck. In the face of the chuck there is a hole that is approx. 3–7 µm smaller than the diameter of the cutter shank. When heated by induction , the chuck expands and the milling cutter can be inserted. When the material cools down and the material contracts as a result, the chuck clamps the tool in a force-fit and precise manner. The disadvantage is that a separate chuck is required for each shaft diameter. Shrink chucks are used in machine tools where the tools have to be changed several times. Due to the defined position of the drill, the drill is always clamped in the machine in the same way and there are no deviations due to different clamping lengths of the drill.
More chucks
Chucks on hand tools (e.g. for clamping interchangeable blades in scalpels or for fixing different needle file inserts in a file handle) often work according to the same principle, but can be mechanically less complex, as work is usually not done at high speeds.
literature
- Heinrich Matuszewski: manual devices . Construction and use, Friedrich Vieweg & Sohn Verlag, Braunschweig 1986, ISBN 978-3-528-04005-5 .
- Bozina Perovic: Devices in machine tool construction . Basics - calculation and construction, Springer Vieweg, Berlin / Heidelberg 2013, ISBN 978-3-642-32706-3 .
- Karl Schreyer: Workpiece clamp . Devices, Springer Verlag GmbH, Berlin / Heidelberg 1949.
- Heinz Tschätsch: Practice of machining technology . Procedure - Tools - Calculation, 7th edition, Friedrich Vieweg & Sohn Verlag, Wiesbaden 2005, ISBN 3-528-44986-1 .
- Günter Spur (Ed.): Manual machining and ablation . Carl Hanser Verlag, Munich 2014, ISBN 978-3-446-42826-3 .
Web links
- Clamping technology (accessed on January 26, 2018)
- Stationary chucks manual, pneumatic, hydraulic (accessed on January 26, 2018)
Individual evidence
- ↑ werkstatt-betrieb.de: Sectional view of a quick-release drill chuck , from the article "Tool holders for drilling", accessed on August 14, 2018
