Centering work on the Lathe.

Odd shaped or square work is often set on the lathe for boring or facing etc. and is often difficult to centre.  There are several ways of doing this depending on the work itself.  If you have a centre punch mark, say where a hole is to be drilled, then you can use a dial or 'finger' indicator in conjunction with  a centering rod.  The centering rod (my term) is made with a length of accurate, ground round bar.  I use a shaft from an old defunct printer.  One end is accurately centre drilled and the other end given a point, I use 60 degrees included.  The work to be centred is mounted on the faceplate or in the 4 jaw independent chuck, depending on the work, and the centre punch mark to be centred is set approximately on centre using a good dead centre in the tailstock.

Centering Work On the Lathe

The tailstock is withdrawn and the 'centering rod' is mounted between the dead centre and the centre punch mark on the work.  if the work is rotated by hand the rod will probable show a wobble, if not you are lucky and the work is centred.  I have no photograph at the moment so a rough sketch will have to suffice to show the idea.

You can now use an indicator of some type to measure the offset of the centre and adjust until the centering rod runs true.  You will then have an accurately set job in the lathe.

I have seen various contraptions used including spring loaded devices, but I have never needed such complications but can see the logic so I may get around to designing and making one some day.  Often another dead centre with rear centre drilled hole (of course), is substituted for the rod.  Takes your choice it's up to each individual to use what is convenient.

Just a point, if you are using a 4 jaw independent chuck, set one opposite pair of jaws accurately first, then concentrate on the other two.  Trying to set all four at the same time will have you running to the psychiatric ward before long and you will take up some other easier hobby such as building a fusion reactor or harnessing dark energy.