Advanced Lathe Operations

 KNURLING

                        Knurling is the operation of squeasing the metal on the surface of a cylindrical workpiece to emboss in a regular pattern small projections and depressions. The pattern may be embossed by pressing a knurling roller against the rotating workpiece. The roller will have the required pattern cut on it and it is hardened. The purpose of knurling is to provide effective gripping surface on the workpiece when operated by hand. Knurling is to be done at low speed.  

Eccentric Turning

If a cylindrical workpiece has two separate axes of rotation, one being out of centre to the other, the workpiece is called eccentric and turning of such multiaxial surfaces is called eccentric turning. Eccentric turning can be done either between centres or in a 4 jaw-independent chuck. It can also be done in a 3 jaw-self centering chuck by placing a shim [a small packing piece] on one of the jaws. The thickness of the shim can be calculated by the formula.

                                         t=K.d

where t= thickness of the shim in mm.

             k is a coefficient to be found in engineering tables and

             d= diameter of the surface by which the work is secured in the chuck ‘d’ is in mm.

                           To do eccentric turning in between centres, first the two ends of the job are faced to the required length. Then the offset centres are marked on both faces with respect to actual centre holes are drilled on a drilling machine. Then the job is held between centres by the offset centres and the eccentric turning is done.

Spinning

Spinning is the operation of forming a piece of sheet metal into required shape by pressing it against a FORMER [pattern]. The former may be made out of wood, metal or plastic. It is held in the spindle and the sheet metal piece is placed over that and supported by the tailstock. While rotating, the sheet metal is pressed against the former with a long broad nosed tool, held in hands and supported on a special tool post. The former will have the external shape of the product. There are special spinning lathes also.

SPRING WINDING

Both, tension and compression springs can be wound on the lathe, the operation being called SPRING WINDING. A MANDREL is held in between centres or in a chuck over which the spring is wound by passing the wire through a small hole in a flat piece, which is held in the tool post. The diameter of the mandrel is calculated, depending on the outside and inside diameters of the required spring, and the elastic modulus of the spring wire. The required path is set on the lathe in the same way as in thread cutting.

                  The arbor, for making the spring, is calculated from the formula.

                               D=K.d

                    Where

                                  D= arbor diameter in mm.

                                  K= coefficient to be found in engineering tables.

                                  d= inside diameter of spring in mm.

The pitch of the spring is to be set larger by 5-8% than specified to compensate for the spring back tendency.