3/8″ Bottoming Tap
A bottoming tap cuts the threads quicker and all the way to the bottom. The picture shows a regular tap where the taper does not allow for threads to be cut as deep. Since I am a woodturner, I have experienced all the little problems you have with threading blanks for turning. Each specie of wood is different, now resin with wood, plain resin, acrylic and stabilized burl all make it difficult for one tool to work great with all of the above.
Having this bottoming tap on hand to use when you suspect threading with the mandrel might not work on a certain blank. Also we listened to your suggestions and concerns and have made an innovative ™improvement to the mandrels by tapering the tapping flute so it starts the threads more like a regular tap. Remember to drill a 5/16″ hole at least 1/4″ deeper than you need for “air” room at the bottom. With this tap and the new Niles™mandrels, you will be able to thread anything!
Lathes Specifications: here is a list of lathe spindle sizes and Morse taper if you are not sure.