I have been asked to show the making of screw. A screw is such an everyday item yet how are they made especially when they are small? I hope this will throw a little light on the The Art of Screw Making.
As used in horology screws must be hardened steel, soft steel is not strong enough
Screw 1; The beginnings, oil hardening steel rod and the 1mm die used to cut the thread on the screw.
Screw 2; The screw has been turned to size, threaded and cut off the rod.
Screw 2a; Now in the lathe the screw head is turned flat and a slight bevel given to the edge of the head.
Screw 3; The screw is heated red hot then quenched in oil, the screw is now dead hard.
Screw 4; Using a screw holding mandrel and the screw head polishing tool the iron disc is used first. The disc is charged with 1200 grit diamond paste, the disc and the screw held in the mandrel are rotated against each other in opposite directions, this quickly removes turning marks.
Screw 5; As shown the head still has remaining turning marks, this requires further dressing against the iron disc.
Screw 6; The turning marks are all gone leaving the screw head with a flat finish and 1200 grit marks.
Screw 7; The iron disc is replaced with a disc of bell metal, 4000 grit diamond paste has been used. Now there screw head is looking smoother and less visible scratches from the previous grit.
Screw 8; Black polish. This is the final stage after using 1/4 micron grit on a boxwood disc,
Screw 9; The screw in place on the Platinum movement holding one of the two balance bridge posts.