Not having a tapered section like a tapered stub mandrel securing the workpiece is
by means of a fixing screw in the end of the mandrel. Because of this it has to
have a step to provide a surface for the workpiece to be secured against.
Provided the mandrel is made a close fit in the workpiece and is used whilst still
in the chuck then a high degree of concentricity is achieved. The outer diameter
can be fully machined but the step in the mandrel and the screw and washer on the
other side prevent this on the sides .
Photo 1 and 2 show a pulley being made. With one side of the pulley having been made,
photo 2, the pulley can be removed, turned over, and refitted and the second side
machined without the need for the top slide angle to be changed. LINK
Do not be confused by what appears to be the mandrel with just a washer on the end
of it, that is two washers. No doubt the screw I was using was just too long.
Photo 3 is a slightly special application, the part being made is a die holder. The
bore for the die has already been made and the shank which will be mounted in a holder
in the tailstock is being made. This must therefore be concentric with the bore for
the die but true to the base of the bore on which the die will sit.
Because of this the part is not being held against the step in the mandrel but on
the mandrel’s end, hence the gap seen in the photograph. LINK