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Summary Of Calculation Formula For Threads

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I. Calculation and tolerance of the external diameter of the external thread of 60° tooth type (GB 197/196)


      a. Calculation of the basic diameter of the middle diameter: The basic size of the thread diameter = thread diameter - pitch × coefficient value.


          The formula indicates: d/D-P×0.6495


          Example: Calculation of the diameter of the external thread M8 thread 8-1.25×0.6495=8-0.8119≈7.188


      b. Common 6h external thread diameter tolerance (based on pitch).


         The upper limit is “0”, and the lower limit is P0.8-0.095, P1.00-0.112, P1.25-0.118, P1.5-0.132, P1.75-0.150, P2.0-0.16, P2. 5-0.17


The upper limit calculation formula is the basic size, and the lower limit calculation formula d2-hes-Td2 is the medium diameter basic size-deviation-tolerance.


         M8 6h medium diameter tolerance value: upper limit value 7.188; lower limit value: 7.188-0.118=7.07.


       c. The basic deviation of the common 6g external thread diameter: (based on the pitch).


          P0.80-0.024, P 1.00-0.026, P1.25-0.028, P1.5-0.032, P1.75-0.034, P2-0.038, P2.5-0.042


         The upper limit calculation formula d2-ges is the basic size-deviation


         The lower limit calculation formula d2-ges-Td2 is the basic size-deviation-tolerance


          Example 6: 6g class medium diameter tolerance value: upper limit value: 7.188-0.028=7.16 Lower limit value: 7.188-0.028-0.118=7.042.


The thread tolerance of 1 or more is based on the coarse teeth, and the thread tolerances of the fine teeth are somewhat changed, but the tolerances are only increased, so the control will not exceed the specification limit, so it is not marked one by one in the above.


                 The diameter of the 2-threaded polished rod blank is in the actual production according to the accuracy of the design requirements and the pressing force of the thread processing equipment, and the diameter of the designed thread is increased by 0.04-0.08, which is the diameter of the threaded rod blank. The company's M8 external thread 6g grade threaded rod diameter is in the range of 7.08 - 7.13.


                 3 Considering the needs of the production process, the lower limit of the intermediate diameter of the actual thread that is not subjected to heat treatment and surface treatment should be kept as far as possible at 6h.


Second, 60 ° internal diameter calculation and tolerance (GB 197 /196)




        a. 6H thread diameter tolerance (based on pitch).


           Upper limit: P0.8+0.125 P1.00+0.150 P1.25+0.16 P1.5+0.180


                        P1.25+0.00 P2.0+0.212 P2.5+0.224


           The lower limit is "0",


           The upper limit calculation formula 2+TD2 is the basic size + tolerance.


           Example M8-6H internal thread diameter: 7.188 + 0.160 = 7.348 upper limit: 7.188 is the lower limit.


        b. The basic diameter of the internal thread is calculated in the same way as the external thread.


            That is, D2=D-P×0.6495, that is, the internal diameter of the internal thread, the diameter of the thread, the pitch, and the coefficient value.


       c. Basic deviation E1 of the 6G thread diameter (based on the pitch).


           P0.8+0.024 P1.00+0.026 P1.25+0.028 P1.5+0.032


           P1.75+0.034 P1.00+0.026 P2.5+0.042


           Example: M8 6G internal thread upper diameter upper limit: 7.188+0.026+0.16=7.374


           Lower limit: 7.188+0.026=7.214


           The upper limit formula 2+GE1+TD2 is the medium diameter basic size + deviation + tolerance


           The lower limit formula 2+GE1 is the medium diameter size + deviation




Third, the calculation and tolerance of the external diameter of the external thread (GB 197/196)



        a. The 6h large diameter upper limit of the external thread is the thread diameter value.


           For example, M8 has a tolerance of φ8.00 upper limit value of "0".


        b. 6h large diameter lower limit tolerance of external thread (based on pitch).


           P0.8-0.15 P1.00-0.18 P1.25-0.212 P1.5-0.236 P1.75-0.265


           P2.0-0.28 P2.5-0.335


           The formula for calculating the lower limit of the large diameter: d-Td is the basic size of the thread large diameter - tolerance.


           Example: M8 external thread 6h large diameter size: upper limit is φ8, lower limit is φ8-0.212=φ7.788