Design and Performance Analysis of a Moveable Groove-tracking Milling Machine for Repairing Thread of Marine Steering Gear Nuts

In the shipping industry, parts of a ship are prone to damage after a long voyage. Due to working under high pressure and high load for a long time, the connecting thread of the nut will get stick, which makes the parts in poor operation. This failure frequently occurs at the nut connection between tiller and rudderstock, as well as between the propeller and the stern shaft. The nuts with damaged threads are often repaired by a method which called "groove-tracking machining". However, due to the huge volume of the nut, generally 300-1,500mm in nominal diameter, it takes lots of time to disassemble, assemble and transport it to the workshop. And there are problems such as finding the origin location of the screw helix, which leads to high maintenance cost for the large nuts. Aiming at repairing damaged internal thread of the nuts for marine steering gear, this paper presents a design of a groove-tracking milling machine, which is moveable and easy to assemble and disassemble. Due to the huge volume of the nut, this design will adopt a structure, which makes the nut fixed and the whole machine built into the nut to repair the thread. Further-more, finite element analysis, kinematics simulation analysis and dynamics analysis are carried out on the main parts by UG NX, which provide necessary reference and theoretical basis for the production and manufacture of this machine.