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ASME B1.30-2002 pdf download

ASME B1.30-2002 pdf download.SCREW THREADS: STANDARD PRACTICE FOR CALCULATING AND ROUNDING DIMENSIONS .
1 GENERAL 1.1 Purpose The purpose of this Standard is to establish uniform and specific practices for calculating and rounding the numeric values used for inch and metric screw thread design data dimensions only. No attempt is made to establish a policy of rounding actual thread characteris- tics measured by the manufacturer or user of thread gages. Covered is the Standard Rounding Policy regard- ing the last figure or decimal place to be retained by a numeric value and the number of decimal places to be retained by values used in intermediate calculations of thread design data dimensions. Values calculated to this Standard for inch and metric screw thread design data dimensions may vary slightly from values shown in existing issues of ACME B1 screw thread standards and are to take precedence in all new or future revisions of ASME B1 standards as applicable except as noted in para. 1.2. 1.2 Metric Application Allowances (fundamental deviations) and tolerances for metric M and MJ screw threads are based upon formulas, which appear in applicable standards. Values of allowances for standard tolerance positions and val- ues of tolerances for standard tolerance grades are tabu- lated in these standards for a selection of pitches. Rounding rules specified below have not been applied to these values but have followed practices of the Inter- national Organization for Standardization (ISO). For pitches, which are not included in the tables, standard formulas and the rounding rules specified herein are applicable. NOTE: IS0 rounding practices, for screw thread tolerances and allowances, use rounding to the nearest values in the R40 series of numbers in accordance with IS0 3. in some cases, the rounded values have been adjusted to produce a smooth progression. Since the IS0 rounded values have been standardized internationally, for metric screw threads, it would lead to confusion if tolerances and allowances were recalculated using B1.30 rules, for use in the USA. 81.30 rounding rules are, therefore, only applicable to special threads where tabulated values do not exist in IS0 standards. Values calculated using the IS0 R40 series values may differ from those calculated using 81.30. in such a case the special thread values generated using 81.30 take precedence.
2.1.4 The final rounded value is obtained from the most precise value available and not from a series of successive rounding. For example, 0.5499 should be rounded to 0.550, 0.55 and 0.5 (not 0.6), since the most precise value available is less than 0.55. Similarly, 0.5501 should be rounded as 0.550,0.55 and 0.6, since the most precise value available is more than 0.55. In the case of 0.5500 rounding should be 0.550,0.55 and 0.6, since the most precise value available is 0.5500. 3 CALCULATIONS FROM FORMULAS 3.1 General Rules 3.1.1 Values for pitch and constants derived from a function of pitch are used out to eight decimal places for inch series. The eight place values are obtained by rounding their truncated ten place values. Seven decimal place values for metric series constants are derived by rounding their truncated nine place values. See para. 4 for thread form constants. Values used in intermediate calculations are rounded to two places beyond the num- ber of decimal places retained for the final value, see Table 1.
(a) Minor Diameter Exceptions for Internal Threads: (1) Minimum Minor Diameter. All classes are calcu- lated and then rounded off to the nearest 0.001 in. and expressed in three decimal places for sizes 0.138 in. and larger. For Class 3B, a zero is added to yield four decimal places. (2) Maximum Minor Diameter. All classes are calcu- lated before rounding, then rounded for Classes l B and 2B to the nearest 0.001 in. for sizes 0.138 in. and larger. Class 3B values are rounded to four decimal places. 3.1.4 Metric screw threads are dimensioned in milli- meters. The final values of pitch diameter, major diame- ter, minor diameter, allowance and thread element tolerances are expressed to three decimal places. 3.1.5 Values containing multiple trailing zeros out to the required number of decimal places can be expressed by displaying only two of them beyond the last significant digit. EXAMPLE: 20 threads per inch has a pitch equal to 0.05000000 and can be expressed as 0.0500. 3.2 Examples The formulas in the examples for inch screw threads in Tables 2,3,4 and 5 are based on those listed in ACME 81.1, Unified Inch Screw Threads. Tables 2 and 3 are based on a size that when converted from a fraction to a decimal will result in a number that has only four decimal places. Tables 4 and 5 are based on a size that when converted will result in a number with infinite numbers of digits after the decimal point. The formulas in the examples for metric screw threads in Tables 6,7,8 and 9 are based on those listed in ACME B1.13M, Metric Screw Threads. Tables 6 and 7 show the use of the tabulated values for allowances and tolerances (in accordance with IS0 965-1) for the calculation of size limits for standard diameter/pitch combinations listed in both IS0 261 and ACME B1.13M. The constant values differ from those used for inch screw threads, in accor- dance with the policy of rounding of this Standard, because metric limits of size are expressed to only three decimal places rather than four.

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