After you gentlemen convinced me to toss the brazed carbide lathe bits and use HSS, I got involved in grinding a threading tool. I have a T&C grinder but I do not have a mag chuck or compound sine plate so I am stuck with using my multi-angle vise or other means.
I have been able to grind a tool that looks like 60° but have been unable to measure it accurately. I have a Celestron microscope and the measurement software is terrible. I ended up visiting my friend with a 10x comparator. He was able to measure the angle and I was within 1/2° on the fat side, i.e. 60.5°. It appears by eye and a loupe to fit the fishtail gage.

Eyebrow threading is a depilation technique which originated in India, although it is also widely practiced in the Middle East. Salons in Western nations offered the service to Middle Eastern clients for decades before European and American women became interested and the popularity of eyebrow threading skyrocketed. Cosmetic Procedures Thread Lift Minimally Invasive Procedure. A thread lift, sometimes referred to as a 'lunchtime lift,' uses absorbable, barbed sutures to offer a tighter, more youthful aesthetic appearance to the face and neck.

This leads to question #1: How does one measure the angle of a threading tool point with accuracy?

Threading Eyebrows

Threading & Boring Project Step 2 A Groovingthe Mechanics

Now that I have a tool ground, I have the daunting task of setting it properly in the lathe tool post. (I retired the lantern style years ago.) All these years I have used the fishtail gage, cut threads, and was none the wiser. Threads are somewhat forgiving if you hit the profile close enough, as the threads distort to a rest state when the fastener is torqued to spec.
This leads to question #2: How does one set the tool accurately in the tool holder?
Just asking as I am trying to do this right after years of muddling.
--earlgo