Tapping unit with protection means

A tapping unit (1), comprising:

• a casing (2) intended to be fixed in front of a workpiece (3) to be machined on a support of a machine tool, and having an interior housing (2a),
• a master template (4), including a bush (4a) with a threaded bore (4b), axially engaged to slide inside the interior housing (2a) of the casing (2),
• locking means (5), preventing the master template (4) from rotating inside the interior housing (2a) of the casing (2),
• a tap-holder (6), including means (6a) for receiving and retaining a tap (7), provided with a threaded section (6b) functionally engaged in the threaded bore (4b) of the master template (4), and including a driving section (6c),
• a rotatably mounted drive shaft (8), including a bore (8a) receiving in longitudinal sliding the drive section (6c) of the tap-holder (6), and loaded in rotation by a mechanical transmission actuated by a motor,
• protection means (12) for allowing axial retraction movement of the master template (4) toward the interior of the casing (2) from a reference position to a first proximal retraction position over a first particular penetration stroke (C1) over which first spring-loading means (13) continuously urge the master template (4) toward its reference position,
• wherein the protection means (12) further allow a supplementary retraction axial movement of the master template (4) toward the interior of the casing (2) from the first proximal retraction position to a second proximal retraction position over a second particular penetration stroke (C2) over which the master template (4) is no longer urged toward the exterior of the casing (2).