The most common methods of determining the positional accuracy of the workpiece on
a faceplate are by means of a centre finder, or a DTI (dial test indicator) testing
some part of, or an item added to, the workpiece.
When the centre finder is being used it will be located into a centre punch mark,
or a centre drilled impression, and the faceplate rotated by hand when any off centre
error will be evident by the finder swinging in a circle. The position of the workpiece
will adjusted until the finder remains static as the faceplate is rotated and if
precision is not necessary then this can be judged visually, otherwise, movement
of the finder will be checked using a DTI as seen in the Photograph.
As shown, this simple device is supported between the workpiece and the tailstock
centre and at this end the finder has a sprung loaded drilled centre. With this compressed
a little by feeding the tailstock it ensures that the working end of the finder remains
firmly in contact with the workpiece as the faceplate is rotated.
Similarly, it will also find a use to position parts in the four jaw chuck. If you
do not posses a centre finder then this will make a simple project for an hour or
so, drawings for this device are included.
This is mostly straight forward but do ensure the body material is running true
when the 60 degree angle is being turned. If you do not have a four jaw chuck so
that it can be set true then using a fixed steady will achieve the required result.
Hold the non pointed end in the three jaw and support the other end using the fixed
steady. With this done the outer end will be running perfectly true enabling the
point to be concentric with the parallel portion of the body.