The trued end of the coupler is now set into the chuck on the lathe. The purpose of truing should be apparent for when the cut is made on the other end, both ends will be made concentric.
Take note that on the lathe chuck, the jaws are numbered and this number is identified on the coupler in the event it is removed so that it can be positioned properly on reinsertion in the chuck. Both ends of the coupler are now concentric.
The tool piece has been changed to a boring bar. In this photo, the bar can be seen how it will plunge into the coupler and the cross slide (the part of the lathe that the boring bar is attached to) will be moved outward. Throughout the boring process, the inside diameter will be checked until it is at the required diameter that you are looking for.
The above photo shows a cross compound set up. The tool piece has been changed back to a cutter. The cross compound will cut the desired taper after the degrees are set. The degree of the taper is determined by the material that the die will be used on.
The taper has been finished. Depending upon how sharp you wish the edge, a whetstone can be used with some light oil and held to the taper as the lathe is slowly turned (not recommended for the inexperienced for this can be hazardous due to the rotating jaws of the chuck but if you need the edge then be careful)
You now have made an inexpensive die for the uniform cutting of dielectrics or leather or any material.
Mikado