Impact driver
Encyclopedia
An impact driver is a tool that delivers a strong, sudden rotational and downward force. In conjunction with toughened screwdriver bits and socket sets
, they are often used by mechanic
s to loosen larger screws (bolts) and nut
s that are corrosively "frozen" or over-torqued
. The direction can also be reversed for situations where screws have to be tightened with torque greater than a screwdriver
can reasonably provide.
Manual impact drivers consist of a heavy outer sleeve that surrounds an inner core that is splined to it. The spline is curved so that when the user strikes the outer sleeve with a hammer, its downward force works on the spline to produce turning force on the core and any socket or work bit attached to it. The tool translates the heavy rotational inertia
of the sleeve to the lighter core to generate large amounts of torque. At the same time, the striking blow from the hammer forces the impact driver down into the screw reducing or eliminating cam out
. This attribute is most beneficial for Philips screw
s which normally cam out as part of their design. It is less beneficial for slot head screws and is not beneficial at all for most other types.
Another type of impact driver uses a motor to automatically deliver rotational forces. These have the advantage of greatly increased speed. They are most often used in construction and manufacturing to replace screwdrivers where speed and operator fatigue are an issue. In some situations however, this type falls short since current designs cannot deliver the downward blow of a manual unit. This can be especially true on very stubborn fasteners. It is a common misconception that motorized impact drivers deliver a downward force when in fact they deliver no downward force at all.
These are not to be confused with the impact wrench
, which is a motorized tool (usually powered by compressed air
), with a similar name and function. These also use a hammering action to apply torque
to fasteners. The difference is that impact wrenches do not provide the positive engagement that impact drivers offer as mentioned above. Otherwise impact drivers and impact wrenches operate in essentially the same fashion.
Socket wrench
A socket wrench is a wrench with interchangeable heads called sockets that attach to a fitting on the wrench, allowing it to turn different sized bolts and other fasteners. The most common form is a hand tool popularly called a ratchet consisting of a handle with a ratcheting mechanism built in,...
, they are often used by mechanic
Mechanic
A mechanic is a craftsman or technician who uses tools to build or repair machinery.Many mechanics are specialized in a particular field such as auto mechanics, bicycle mechanics, motorcycle mechanics, boiler mechanics, general mechanics, industrial maintenance mechanics , air conditioning and...
s to loosen larger screws (bolts) and nut
Nut (hardware)
A nut is a type of hardware fastener with a threaded hole. Nuts are almost always used opposite a mating bolt to fasten a stack of parts together. The two partners are kept together by a combination of their threads' friction, a slight stretch of the bolt, and compression of the parts...
s that are corrosively "frozen" or over-torqued
Torque
Torque, moment or moment of force , is the tendency of a force to rotate an object about an axis, fulcrum, or pivot. Just as a force is a push or a pull, a torque can be thought of as a twist....
. The direction can also be reversed for situations where screws have to be tightened with torque greater than a screwdriver
Screwdriver
A screwdriver is a tool for driving screws and often rotating other machine elements with the mating drive system. The screwdriver is made up of a head or tip, which engages with a screw, a mechanism to apply torque by rotating the tip, and some way to position and support the screwdriver...
can reasonably provide.
Moment of inertia
In classical mechanics, moment of inertia, also called mass moment of inertia, rotational inertia, polar moment of inertia of mass, or the angular mass, is a measure of an object's resistance to changes to its rotation. It is the inertia of a rotating body with respect to its rotation...
of the sleeve to the lighter core to generate large amounts of torque. At the same time, the striking blow from the hammer forces the impact driver down into the screw reducing or eliminating cam out
Cam out
To cam out is a process by which a screwdriver slips out of the head of a screw being driven once the torque required to turn the screw exceeds a certain amount....
. This attribute is most beneficial for Philips screw
Henry F. Phillips
Henry F. Phillips was a U.S. businessman from Portland, Oregon. The Phillips-head screw and screwdriver are named after him....
s which normally cam out as part of their design. It is less beneficial for slot head screws and is not beneficial at all for most other types.
These are not to be confused with the impact wrench
Impact wrench
An impact wrench is a socket wrench power tool designed to deliver high torque output with minimal exertion by the user, by storing energy in a rotating mass, then delivering it suddenly to the output shaft.Compressed air is the most common power source, although electric or hydraulic...
, which is a motorized tool (usually powered by compressed air
Compressed air
Compressed air is air which is kept under a certain pressure, usually greater than that of the atmosphere. In Europe, 10 percent of all electricity used by industry is used to produce compressed air, amounting to 80 terawatt hours consumption per year....
), with a similar name and function. These also use a hammering action to apply torque
Torque
Torque, moment or moment of force , is the tendency of a force to rotate an object about an axis, fulcrum, or pivot. Just as a force is a push or a pull, a torque can be thought of as a twist....
to fasteners. The difference is that impact wrenches do not provide the positive engagement that impact drivers offer as mentioned above. Otherwise impact drivers and impact wrenches operate in essentially the same fashion.