Random orbital sander
Random orbit sanders, also called Dual-Action or D.A. sanders (referring to the rotation of the disk and the head) are hand-held power sander
A sander is a power tool used to smooth wood and automotive or wood finishes by abrasion with sandpaper. Sanders have a means to attach the sandpaper and a mechanism to move it rapidly contained within a housing with means to hand-hold it or fix it to a workbench. Woodworking sanders are usually...

s where the action is a random orbit. They were first introduced in the early 1990s and quickly became tremendously popular. Random orbit sanders combine almost the speed and aggressiveness of a belt sander
Belt sander
A belt sander is a machine used to sand down wood and other materials for finishing purposes. It consists of an electrical motor that turns a pair of drums on which a seamless loop of sandpaper is mounted. Belt sanders can be either hand-held, where the sander is moved over the material, or...

, with the ability to produce a finer finish than that available from a standard, slow speed, orbital finishing sander.

The random orbit is produced by simultaneously spinning the sanding disk and moving it in an ellipse, which ensures that no single part of the abrasive material travels the same path twice. Because of this unique random sanding action, the tool does not leave swirl marks, and it is not sensitive to the direction of the wood grain
Wood grain
In speaking of wood the term grain refers to the alternating regions of relatively darker and lighter wood resulting from the differing growth parameters occurring in different seasons . The term is used in several ways. Perhaps most important is that in woodworking techniques...

. This makes it work very well when sanding two pieces of wood
Wood is a hard, fibrous tissue found in many trees. It has been used for hundreds of thousands of years for both fuel and as a construction material. It is an organic material, a natural composite of cellulose fibers embedded in a matrix of lignin which resists compression...

 that meet at right angle
Right angle
In geometry and trigonometry, a right angle is an angle that bisects the angle formed by two halves of a straight line. More precisely, if a ray is placed so that its endpoint is on a line and the adjacent angles are equal, then they are right angles...

s. Random-orbital sanders use sandpaper
Sandpaper, also known as glasspaper, is a heavy paper with abrasive material attached to its surface.Sandpaper is part of the "coated abrasives" family of abrasive products. It is used to remove small amounts of material from surfaces, either to make them smoother , to remove a layer of material...

 disks and many random-orbit sanders now come with dust collectors
Dust collection system
A dust collection system is an air quality improvement system used in industrial, commercial, and home production shops to improve breathable air quality and safety by removing particulate matter from the air and environment. Dust collection systems work on the basic formula of CAPTURE, CONVEY and...

. Disks are attached using either pressure sensitive adhesives or a hook and loop system. On models equipped with a dust collection feature, a vacuum
In everyday usage, vacuum is a volume of space that is essentially empty of matter, such that its gaseous pressure is much less than atmospheric pressure. The word comes from the Latin term for "empty". A perfect vacuum would be one with no particles in it at all, which is impossible to achieve in...

effect sucks sanding dust through holes in the paper and pad, feeding it to a bag or canister.
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