Masonry locator moves 250kg pieces with lead screw precision
The 'Dean's Eye' rose window at Lincoln Cathedral has recently been
restored, a project that involved replacement of heavy masonry sections
in the window's stone tracery. Working at a height of 150m from the
ground, called for safe operating procedures, particularly concerning
safe and secure access to the restoration site. One of the specialist
contractors on the job, Scorpion Lifting Systems designed a bespoke
manipulating rig for this purpose, specifically to locate, grip and
manoeuvre four carved stone pieces weighing up to 250kg apiece.
The Y- and Z-axis movements of this rig are provided by Huco lead screws.
The Y-axis lead screw drives the extending reach arms, and comprises two
elements joined by a rigid steel coupling, also supplied by Huco. The two
sections have opposite hand threads and are anchored at either end by
lead screw drivers. The arms run in two precision channels that are, in
turn, attached to the Z-axis mechanism by two heavy bolted angle irons.
The Z-axis lead screw lifts and lowers the device slide-ways along which
the stonework and fixtures move in the Z plane. It is actuated by means
of a height adjustment wrench. A large thrust bearing is fitted between
the lead screw supporting flange and floating bronze bush to reduce the
effort required to move the Z-axis slide-way.
The steel lead screws feature rolled threads for high tensile strength
and accuracy. They are also resistant to abrasion and corrosion, and
provide a maximum lead deviation of just 0.15mm over a 300mm length.