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The Jacobs Taper (abbreviated JT) is commonly used to secure drill press chucks to an arbor. The taper angles are not consistent varying from 1.41° per side for No. 0 (and the obscure # 2 + 1 ⁄ 2) to 2.33° per side for No. 2 (and No. 2 short). There are also several sizes between No. 2 and No. 3: No. 2 short, No. 6 and No. 33.
Several machine collets (top and centre) and a dismantled pin chuck (below). Generally, a collet chuck, [3] considered as a unit, consists of a tapered receiving sleeve (sometimes integral with the machine spindle), the collet proper (usually made of spring steel) which is inserted into the receiving sleeve, and (often) a cap that screws over the collet, clamping it via another taper.
The chuck may be held against the taper with a threaded retainer ring (large thin nut), typically wrenched with a spanner wrench of the pin or hook variety. The peak of popularity for building this type of spindle nose was the 1940s and 1950s. The chuck may be held against the taper with cam-lock posts that wedge into a stuck-fast position.
Both the tool and socket have a slight taper. The contemporary square drive screw has all but replaced the Robertson screw proper and is commonly referred to as a Robertson because it has practically identical drive dimensions and the same colour identification system, but the contemporary square drive socket has parallel sides rather than tapered.
For Morse taper-shank drill bits, the standard continues in 1/64 inch increments up to 1¾ inch, then 1/32 inch increments up to 2¼ inch, 1/16 inch increments up to 3 inches, 1/8 inch increments up to 3¼ inches, and a single 1/4 inch increment to 3½ inches. One aspect of this method of sizing is that the size increment between drill bits ...
Over time, various chuck designs have been invented, and modern chucks can grasp and drive this shank effectively. It has been difficult to find a reference to the included angle of the taper, but 7 different bits were measured, and they all had an included angle of 8 ± 0.25 degrees. Easy to make in a forge
The drill will grasp the upper end of a bit called the shank in the chuck. Drills come in standardized drill bit sizes. A comprehensive drill bit and tap size chart lists metric and imperial sized drills alongside the required screw tap sizes. There are also certain specialized drill bits that can create holes with a non-circular cross-section.
The number refers to the Association for Manufacturing Technology (formerly the National Machine Tool Builders Association (NMTB)) taper size of the tool. A CAT-40 toolholder A boring head on a Morse taper shank. An improvement on CAT Tooling is Bridgeport Taper (BT) Tooling, which looks similar and can easily be confused with CAT tooling.