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Twist drill. From Wikipedia, the free encyclopedia. ... Download as PDF; Printable version; Languages. Add links. This page was last edited on 8 April 2022, at 20:54 ...
A gimlet is a hand tool for drilling small holes, mainly in wood, without splitting. It was defined in Joseph Gwilt's Architecture (1859) as "a piece of steel of a semi-cylindrical form, hollow on one side, having a cross handle at one end and a worm or screw at the other".
The pilot drill may be a standard twist drill, another type of drill bit appropriate for the material, or, when the primary purpose is precisely locating a hole, may be made with a short, stiff center drill. The pilot hole also reduces the power needed to turn a large drill bit, and reduces the large bit breakage risk.
The twist drill bit is the type produced in largest quantity today. It comprises a cutting point at the tip of a cylindrical shaft with helical flutes; the flutes act as an Archimedean screw and lift swarf out of the hole. The modern-style twist drill bit was invented by Sir Joseph Whitworth in 1860.
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It is one of the most widely used types, and is particularly common on the shank of taper-shank twist drills and machine reamers, in the spindles of industrial drill presses, and in the tailstocks of lathes. The taper angle of the Morse taper varies somewhat with size but is typically 1.49 degrees (around 3 degrees included).
The geometry of a hole drilled in metal by a twist drill may not be accurate enough (close enough to a true cylinder of a certain precise diameter) and may not have the required smooth surface finish for certain engineering applications. Although modern twist drills can perform excellently in many cases—usually producing sufficiently accurate ...