Needlegun scalers or needle-guns are a tool used in metalwork applications as diverse as home repair, automotive repair and shipboard preservation.
Used to remove rust, mill scale, and old paint from metal surfaces, it operated pneumatically by abrasion with metal pins, often refered to as fine chisels. The tool forces these needles against a work surface at variable speeds up to around 5,000 times per minute. Different models offer choices of number of needles, operating speed, and power levels. These models use compressed air. Although electrical needle-guns do exist, they are not popular as they aren't considered efficient. In a pneumatic unit, compressed air forces a piston forwards and backwards. This movement causes the needles to move back and forth against the work surface.
The needle gun has many advantages over other scaling tools. Mainly that the needles automatically adjust themselves to contours, making the tool a good choice for cleaning curved and irregular surfaces. Needle guns can clean an area to bare metal in seconds, and compares well to other scaling tools in terms of accuracy and precision.
It is recommended that before needlegunning, a surface be prepared by removing oil, grease, dirt, chemicals and water-soluble contaminants. This can be done with solvents or with a combination of detergent and fresh water. They are used most effectively by holding it at a 90° angle to the work surface. It is recommended that an area no larger than six to eight inches be cleared at once. Two to three passes over an area is generally sufficient to clean it. Then the process is repeated until the desired area is completed. Over use, and excessive air pressure to the tool can result in dimpling of the working surface.