Tapped hole

See also: Hole (homonymy)

A tapped hole is the form complementary to a Vis or threaded Tige. Technically it is about a clearing hole in which one operates a Filetage. This operation also bears the name of tapping.

A nut has a tapped hole generally emerging (if not, they are known as " borgnes" ).

The tapping of a hole is obtained according to two great principles

  • by generation (tool of form traversing a propeller according to the axis of the hole, in turning).
  • by screwing of a Tap in the clearing hole. Method recommended for standard dimensions.

Representation in draftsmanship

Method of layout

In Draftsmanship one uses same convention as for threading. It is advisable to carry out the drawing of a tapping in the order suggested in order not to make errors. In a cut (the most representative case):
  • the contour of the part is in strong feature, in particular the clearing hole which is of diameter equal to the reduced nominal diameter of the step value. The hatchings are thus based on this contour.
  • a strong feature, except for emerging tappings, delimits, in the axial sight, the threaded part (last net). It is the only case in of draftsmanship, or two strong features cross (1).
  • the hollow of the net is represented:
    • in an axial sight by two continuous lines and in fine feature on the side of the matter (thus outside) distant one of the other of the value of the nominal diameter,
    • in a radial sight by an incomplete circle (3/4) with the nominal diameter.
  • if these entities are hidden (except hatchings), they are carried out in fine stopped feature.

(1) the other cases always correspond to 4 convergent features. Theoretical situation

Assembly screw and tapping

The same rules in the case of apply the drawing of the assembly of the screw and its nut, with however an additional constraint: the details of the screw (seldom crossed) have priority. What amounts sticking the opaque drawing of the screw on that of tapping.

Remarks concerning the hole not emerging

For the tappings carried out using a tap, it is not possible to extend the operation until the bottom of the hole. It is advisable to at least hold a length equal to the nominal diameter, corresponding to the length not filetable (tap starts). The strong feature thus materializes the limit beyond which the hole is regarded as not threaded.

Depth of tapping

The screw draws on the nets. A too strong tightening can involve of it the rupture (screw or tapping fair). One recommends a depth of tapping allowing the screw installation of:

  • of 1,5 times the nominal diameter in hard metals (steel);
  • of 2 times the nominal diameter in tender metals (copper or aluminum alloy).

The standard nuts are thick of approximately once the nominal diameter. That comes owing to the fact that the materials are sufficiently resistant.

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