c-g-designs

TORQUES :

          We are often asked at what torque a given screw must be tightened on one of our mechanims

          The answer might seem to be simple,but some indications are necessary at first :

          1°)Material for hollow hexagonal capscrews (Allen) :

          The ISO Norm describe the screws materials following their mechanical properties by a numeric method with 2 numbers.For the screws of concern, it is established as follows :

                      8.8

                    10.9

                    12.9

                    14.9

          In which :

          -The first number correspond to the 1/10th of the traction resistance expressed in Megapascals(MPa).

          -The second number multiplied by the first  represent the 1/10th  of the elastic limit expressed in Megapascals (MPa).

          Example : Screw 10.9

          ---Traction resistance : 10 x 100 = 1000MPa/sq.mm.

          ---Elastic limit : 10 x 9 x 10 = 900MPa/sq.mm.

          It can be seen that the quality difference can be important and condition the torque admiissible for the screw and of course its long term capacity.

          2°) Denomination and minimal quality of the hollow hexagonal capscrews :

          DIN912 : Socket head capscrew : 8.8 , 10.9.

          DIN913 : Socket head setscrew, flat tip : 12.9 , 14.9.

          DIN914 : Socket head setscrew, pointed tip : 12.9 , 14.9.

          DIN 7884 Socket head capscrew (low head) : 10.9.

          DIN 79991 Socket head capscrew (flat head) : 10.9.

          3°) Tightening to the required torque :

          It is recommended to check the contact surfaces to be clean and smooth .

          For a tightening to the maximal torque accuracy, it is recommended to slightly oil the contact surfaces to avoid excess friction possibly altering the torque precision.

          We use exclusively on our mechanisms  the following screws, of a renowmed manufacturer and of quality class at least equal to 10.9. Therefore the torques listed belpw correspond to those specifications :

          We cannot guarantee the use of screws who does not correspond to the quality class we recommend.

          4°) Recommended torques :

---Screws M4x0,7 DIN 912 or 7984 =    4,2 Newton/metre or 3,10 lbs/foot.

---Screws M5x0,8,DIN 912 or 7991=  8 Newtpn/metre or 5,9 lbs/foot.

---Screws M6x1 DIN912 or DIN 7991 = 14 Newton/metre or 10.3 lbs/foot.

          In case a torque screwdriver or wrench is not available, it can be alternatively used a LONG end Allen key and tighten with finger pressure at the end of the llong end of the wrench until the flex of the key is felt .

                    R.G.C

                    05/2015