I have spent a very long and unproductive day trying to cut a 5/16-24 thread on a cut-off piece of 5/16 bolt. I knew things were not going to go well when I could not get the
*never-previously-used* die to even bite. I chamfered, then chamfered again, nothing. eventually I made the tip almost conical. I got some purchase but a) the effort to cut was disproportionate and b) the end result was a thread which was skewed - and not subtly! I tried again with another piece of 5/16 rod - same result.I hit the books to see if I omitted something glaring. Most of the texts I have are big on starting *taps* straight but they did not stress the dies so much.
In the end I borrowed the tap technique: I gripped the rod in the chuck of my drill press. I clamped the die in my drill press vise (there is a little shoulder that allows it to rest flat). I raised the table and centered and clamped the vise with the rod touching. I turned the rod with a pair of vise-grips while simultaneously feeding the spindle (it would be really nice to have three hands!). After the first turn the feed took care of itself. This way I cut a reasonably straight thread but the effort was much harder than I expected. Also, the vise-grips make a mess of the rod.
I tried it again with the cut-off bolt. This time I turned the spindle of the drill press directly by a makeshift lever improvised from the same stock and inserted into the chuck key holes. It was even harder to cut this time (I checked the diameter etc. - all identical).
I should mention that the whole workshop was swimming in Rapid Tap at the end - no dry cutting here.
I suspect that the die is crap and I will go and get another one but the whole process brought up some interesting questions. The most important of them is: How does everyone manage to get a straight thread when die cutting?
I think the method I use is OK provided the workpiece *can* be held in a chuck but if not, I am stumped.
BTW, if using a drill press to start a tap in a hole how do you turn the tap? Do you grind flat spots on your taps to get a better wrench purchase?