Metric Keys and Keyways Machinery's Handbook, 31st Edition
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KEYS AND KEYSEATS
Metric Square and Rectangular Keys and Keyways The ANSI/ASME B18.25.1M (Withdrawn) standard covers requirements for square and rectangular parallel keys and keyways intended for both alignment of shafts and hubs, and transmitting torque between shafts and hubs. Keys covered by this standard have a rel- atively tight width tolerance. The deviations are less than the basic size. Keys with greater width tolerance and with deviations greater than the basic size are covered by ANSI/ ASME B18.25.3M (Withdrawn). All dimensions in this standard are in millimeters (mm). Comparison with ISO R773-1969 and 2491-1974.— This standard is based on ISO Stan- dards R773-1969, Rectangular or Square Parallel Keys and their corresponding key ways, and 2491-1974, Thin Parallel Keys and their corresponding keyways (dimensions in millimeters). Product manufactured to this standard will meet the ISO standards. Be- cause of tighter width tolerances in this standard, products manufactured to the ISO stan- dard may not meet the requirements of this standard. This standard differs from ISO in that it: a) does not restrict the corners of a key to be chamfered but allows either a chamfer or a radius on the key; and b) specifies a key mate rial hardness rather than a tensile property. Tolerances.— Many of the tolerances shown in Table 1 and Table 2 are from ANSI/ASME B4.2 (ISO 286-1 and ISO 286-2). As a result, in addition to plus-minus tolerances which are common in the United States, some are expressed as plus-plus or minus-minus de- viations from the basic size. For further interpretation of these tolerances refer to ANSI/ ASME B4.2 or ISO 286. Designation.— Keys conforming to this standard shall be designated by the following data, preferably in the sequence as follows: a) ASME document number; b) product name; c) nominal size, width ( b ) × height ( h ) × length; d) form; and e) hardness (if other than non-hardened). Example: ANSI/ASME B18.25.1M (Withdrawn) square key 3 × 3 × 15 form B. ANSI/ASME B18.25.1M (Withdrawn) rectangular key 10 × 6 × 20 form C hardened Preferred Lengths and Tolerances.— Preferred lengths and tolerances of square and rectangular keys are shown below. Tolerances are JS16. To minimize problems due to lack of straightness, key length should be less than 10 times the key width. Length ± Tolerances Length ± Tolerances 6 0.38 90, 100, 110 1.10 8, 10 0.45 125, 140, 150, 180 1.25 12, 14, 16, 18 0.56 200, 220, 250 1.45 20, 22, 25, 28 0.65 280 1.60 32, 36, 40, 45, 50 0.80 320, 360, 400 1.80 56, 63, 70, 80 0.95 Material Requirements.— Standard steel keys shall have a Vickers hardness of 183 HV minimum.HardenedkeysshallbealloysteelthroughhardenedtoaVickershardnessof390to 510 HV. When other materials and properties are required, these shall be as agreed upon by the supplier and customer. Dimensions and Tolerances.— Dimensions and tolerances for square and rectangular parallel keys are shown in Table 1. Recommended dimensions and tolerances for keyways are shown in Table 2.
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