A needlegun scaler or needle-gun is a tool used in metalwork applications as diverse as home repair, automotive repair and shipboard preservation.[2][3][4] The tool is used to remove rust, mill scale, and old paint from metal surfaces.[5]
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A needle gun has a set of very fine chisels known as needles.[2] The tool forces these needles against a work surface at variable speeds up to around 5,000 times per minute.[2][5] Different models offer choices of number of needles, operating speed, and power levels.[2] Many models use compressed air, although electrical needle-guns do exist.[2][6]
In a pneumatic unit, compressed air forces a piston forwards and backwards.[2] This movement causes the needles to move back and forth against the work surface.[2]
The needle gun has advantages over other scaling tools. Its main advantage is that the needles automatically adjust themselves to contours, making the tool a good choice for cleaning irregular surfaces.[5] A needle gun can clean an area to bare metal in seconds, and compares well to other scaling tools in terms of accuracy and precision.[2]
It is recommended that before needlegunning, a surface be prepared by removing oil, grease, dirt, chemicals and water-soluble contaminants.[4] This can be done with solvents or with a combination of detergent and fresh water.[4]
Then, the needle gun is used to remove rust, loose scale, and paint, leaving bare metal.[4] It is used most effectively by holding it at a 90° angle to the work surface.[4] It is recommended that an area no larger than six to eight inches be cleared at once.[4] Two to three passes over an area is generally sufficient to clean it.[4] Then the process is repeated until the desired area is completed.[4]
Prior to painting, it is desirable to feather any edges between metal and old paint.[4] It is also important to check the surface for oil deposited during chipping, and if necessary, clean the area with solvents.[4] Since bare metal surfaces will flash rust soon after exposure to the atmosphere, paint should be applied as soon as possible after chipping.[4] If flash rusting occurs prior to coating, further chipping, cleaning and sanding may be necessary.[4]
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