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    ture set. The additional clamping takes precedence in most cases.
    Regardless of the clamping sequence, it is the main clamping that
    is solved prior to the additional clamping.
    4.1 General solution concept of main clamping fixture
    On a horizontal machining centre in one clamping, a maximum
    of four faces of the workpiece are workable. When solving the
    main clamping, one must try to find a position for the workpiece
    in the workspace a of machining centre in which the machining
    of all the connected faces is possible. In this way the greatest
    accuracy of the workpiece can be obtained and the accuracy re-
    quirement and the complexity of the fixture are the lowest. This
    position of the workpiece is called the “technologically ideal
    workpiece position”. The fixture determined in this way is the
    best possible fixture solution.
    However, in several cases the disposition of connected faces
    means that the workpiece can not be held in a technologically
    ideal workpiece position. In this case, it is necesary to find a pos-
    ition of the workpieces in which at least the machining of strictly
    connected faces is possible in one clamping. In other words, the
    loosely connected faces in this stage are left out of consideration.
    In this way, the fixture solution is still “fair”, but the accuracy
    requirements refer only to the parallelism, or rather to the per-
    pendicularity of any fixture surfaces.
    If this attempt is not successful, then one must give up the
    idea of machining all of strictly connected faces in one clamp-
    ing. There are also cases when not the entire face, but only the
    strictly connected features (holes) on the face are workable with
    other strictly connected faces in one clamping (see Sect. 4.1.3).
    Lastly, when none of these attempts is successful the strictly
    tolerance-related features must be machined in separate clamp-
    ings. In this case, the accuracy requirements of the fixture are
    very high.
    Taking into consideration the abovementioned aspects, four
    strategies are devised for solving the main clamping.
    4.1.1 Technologically ideal clamping
    This strategy is aimed at finding the position of the workpiece
    in the machine workspace, which would allow machining of all
    the connected faces in one clamping. The potential position of
    a workpiece in the machine workspace is determined from the
    requirement that all connected faces should be machined in one
    clamping. Depending on the plane locating type, this can be for-
    mulated in the following manner:
    • In the case of horizontal plane locating type pos1, the plane
    locating face and its opposite face must not be tolerance-
    related faces, because it is not possible to machine them
    together with other faces in the same clamping.
    • For a vertical plane locating type pos2, the plane locating
    face, the face which is facing the machine table, and its op-
    posite face, must not be tolerance-related faces.
    In order to select the workpiece position, it should be satisfactory
    for both plane and side locating and clamping (Fig. 7). Since the
    horizontal plane locating (pos1) allows machining of four faces
    (while pos2 allows only three faces to be machined) and the fix-
    ture construction is simpler, the system first attempts to generate
    a fixture solution for horizontal plane locating type. If that at-
    tempt fails, a second attempt is made at solving the fixture for
    vertical plane locating.
    Suitability for plane locating. The selected workpiece position
    is suitable for plane locating if the plane locating face contains
    surfaces which are suitable for plane locating. If the workpiece
    position is suitable for plane locating, then in the next step,
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