This diversion into insanity came about due to one of Joe Pie's videos.
He recently did a video on making an 0-80 nut with a tap. Somewhere in the comments single pointing 0-80 came up. I don't know if he meant internal or external. I've been there done that with external 0-80 single point; so I decided to go for broke and go for single pointing an 0-80 internal thread.
I started off by turning up a tool blank in O-1. The blank was then hardened and ground for clearance. This tool broke on the second pass during my first attempt.
A second tool was produced that was not heat treated. Things went well on the second attemp until the tool wiped out the threads due to the tool pushing off. In hindsight, this is what caused the first tool to break. I had used a surface gage aligned to a center in the tailstock to set the tool height. This was a flawed method at this scale.
A third attempt was made this morning and was successful. Taking what I had learned from the previous two failures; the tool height was set by facing a point on the material to be threaded. (The original set height was too low from the surface gage.) Due to the scale of this exercise, I elected to drill for 50% thread engagement using a No. 55 drill (.052) (1.32mm). Every incremental pass was cut twice to ensure that the tool would not push off.
I really wanted to post a video of this; but my only way of posting video anymore is with my I-Pad. Unfortunely, I could only take blurry video with it. I do have video of the first attempt, but it is pretty much useless.
Why do this at all? The only way to get good at something is to push yourself.
-Bob