CNC Milling of Fasteners in 3D

Small features, but the joint depends on them

A cotter pin or a lockwire only holds if its hole lines up with the slot or the next part, so the hole's position matters as much as its size. Safety wiring and cotter pinning follow set practices, NASM33540 being the common one, and cotter pins themselves are standardized in ASME B18.8.1.

These are standard features as well as specials: ASME B18.3 covers socket head cap screws with drilled heads for lockwire, and ASME B18.2.2 covers slotted nuts for cotter pins. Milling in the same shop as the turning keeps the part, its heat and its drawing together.

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Vertical machining centre with a 4th axis: the spindle stays above the part and the rotary unit turns it between features. The flats are milled with a 90° indexable face mill, a steel body carrying screw-clamped carbide inserts: their bottom edges cut a face and their square outer edges cut a shoulder. The round nut is milled to a hex nut one flat per pass as the table carries it under the cutter along its axis, and the nut is turned 60° between flats for a hex of six flats (90° would give a square of four: geometry). The same cutter mills the collar stud's drive hex from its turned pilot, the square edges of the inserts forming the shoulder as the saddle carries the stud under it. Twist-drill chip flow as described in machining texts; right-hand cutters, drills and nuts turn clockwise seen from the driving end. Threads 1 in.-8 UNC (ASME B1.1; UNC up to 1 in. per ASTM A962) and 1/2-13 for the socket head cap screw (ASME B18.3, which also covers drilled heads for lock wire). The hex nut is drawn to the proportions of a 1 in. heavy hex nut in ASME B18.2.2; the round nut is turned a little under the hex's largest across-corners size, so small round lands remain at the corners. The castle nut's proportions and its slots are illustrative. The screw's lock-wire holes are laid out as on catalogue drilled-head socket cap screws: two straight holes through the head on diameters at 90° to each other, square to the axis at mid head height and crossing at the axis, so each goes in through the side, across the hex socket and out of the far side; that gives four openings 90° apart round the head, and the holes break into the socket's walls. The first is drilled through two opposite flats of the socket and the second, with the screw turned 90°, through two of its corners; the hole size, about 0.06 in., is illustrative. Each part is a separate piece: nothing is assembled. The machine, tool changer, tools, micrometer and lock wire are generic; spindle speeds are slowed and feeds sped up so the cut can be seen, and no speeds, feeds or tolerances are given.