Industrial Metalworking Chucks
Any industrial metalworking tool that relies upon rotation uses chucks. From drills to lathes and CNC mills, chucks are everywhere in the metal and woodworking industries. The key to understanding chucks is that while holding something still is easy, holding something that moves can be very hard. Not only does the chuck have to resist gravity, it has to resist rotational force and do so from a range of angles.
Lathe vs. Mill Chucks
The biggest difference between lathe and drill chucks is that lathe chucks hold the workpiece while mill chucks hold the cutting head. Just like industrial drill chucks, mill chucks are designed to hold a relatively small range of sizes based on the tool heads used. This also means that lathe chucks often have to be significantly stronger due to the fact they have to hold much greater rotating masses. However both types of chucks still have to deal with the same kinds of forces at work.
Types of Chucks
Most standard chucks rely on two or more jaws to hold the workpiece or tool in place. The majority are self-centring in that the jaws move as a unit so that the rotating mass is always centred on the axis of rotation to reduce stress and maximise control. Independent jaw lathe chucks usually have a minimum of four jaws and allow you to adjust the position independently for irregular shaped pieces or off-centre work. Some even reverse so you can hold a piece from the inside if necessary. Combination chucks support either self-centring or independent modes for maximum flexibility.
Where most traditional chucks rely on jaws, magnetic chucks rely on magnetic fields. These chucks can only work with ferrous metals such as steel but have the advantage that you have a flat surface to mount on. Permanent magnets provide the simplest approach, as they just work. Electromagnets offer more hold, but require a power supply and produce heat in operation. Electro-permanent chucks require a current to activate and deactivate but not to maintain their hold.
Collet chucks use a cylindrical opening rather than discrete jaws. They are best suited to small pieces and allow more rapid changes. Lighter and narrower than standard chucks, collet chucks have less rotational inertia so they are better for high speed operations. However they are also less flexible in the size ranges they can accept.