I am finishing end plates, and that involves a lot of tedious hand work and a lot of waiting for the tumbler to do its job. There is a feeling that no progress is being made. So as a remedy, I am making the crank screws. At least something seems to be getting done.
Small screws (this one is 8-32) are most quickly cut with a threading die. The problem is starting the die; it is likely to chew up the end of the screw before biting in and cutting. So my foolproof scheme is to make a blank longer than is needed, and then turn a small diameter at the end. Here is a screw blank properly prepared.
The depth of a 32/inch thread is about 0.027 inch, and the reduced diameter here is about 0.027 less than the full diameter of 0.164. It is applied to the last 0.100 of the screw, enough length for 3 threads. You can see a “neck” behind the area to be threaded; it has nothing to do with starting the thread.
The threading die readily engages the reduced diameter at the end. And by the time it reaches the full diameter, it is gripping the blank very well.
So all I have to do is turn the crank, no fiddling to get the die started.
Update 15 Nov 2012: I am beginning to realize that the quality of the threading die is a factor. Several of the dies that I have will climb right up onto a full diameter, without any lead-in diameter as I described here. This saves a lot of time when making several screws; you don’t have to go back and trim the end. When I originally wrote this post, I was using a die that may not have been shaped well.