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For both of these rules of thumb (85%/90% and major minus pitch), the tap drill size yielded is not necessarily the only possible one, but it is a good one for general use. The 85% and 90% rules works best in the range of 1 ⁄ 4 –1 in (6.4–25.4 mm), the sizes most important on many shop floors. Some sizes outside that range have different ...
where is the tap drill size, is the major diameter of the tap (e.g., 10 mm for a M10×1.5 tap), and pitch is the pitch of the thread (1.5 mm in the case of a standard M10 tap) and so the correct drill size is 8.5 mm. This works for both fine and coarse pitches, and also produces an approximate 75% thread.
A counterbore hole is typically used when a fastener, such as a socket head cap screw or fillister head screw, is required to sit flush with or below the level of a workpiece's surface. Whereas a counterbore is a flat-bottomed enlargement of a smaller coaxial hole, a countersink is a conical enlargement of such.
Trepans usually have multiple carbide inserts and rely on water to cool the cutting tips and to flush chips out of the hole. Trepans are often used to cut large diameters and deep holes. Typical bit diameters are 6–14 in (150–360 mm) and hole depth from 12 in (300 mm) up to 71 feet (22 m).
N · 0.1 mm; From 14.0 through 25.0 mm, sizes are defined as follows, where M is an integer from 14 through 25: M · 1 mm; M · 1 + 0.25 mm; M · 1 + 0.5 mm; M · 1 + 0.75 mm; In smaller sizes, bits are available in smaller diameter increments. This reflects both the smaller drilled hole diameter tolerance possible on smaller holes and the ...
The lower image is a plain plug gauge used to check the size of a hole; the green end is the go, and the red end is the no-go. The tolerance of the part that this gauge checks is 0.30 mm, where the lower size of the hole is 12.60 mm and the upper size is 12.90 mm, every size outside this range is out of tolerance .
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The fluted countersink cutter is used to provide a heavy chamfer in the entrance to a drilled hole. This may be required to allow the correct seating for a countersunk-head screw or to provide the lead in for a second machining operation such as tapping. Countersink cutters are manufactured with six common angles, which are 60°, 82°, 90 ...