(08-04-2013, 03:03 PM)dallen Wrote: why is it that the inserts that I have, have no flat on the point.
DA
What is the insert designation that you have? There are many types for threading, the two most common being 16ER/IR (3ER/IR in Vardex parlance) and Top Notch style. The 16ER (as well as 6ER, 11ER, 22ER and 27ER) are the triangular lay down style which can be either full profile pitch specific or "general purpose" partial profile A60 or AG60 for threads ranging from 16-48 and 8-48 respectively. Those will have a .002" radius on each tip. It's a compromise between a true Sharp V thread and a true UN thread. The pitch specific full profile ER/EL/IR/IL series has a radius of the proper dimension for each thread pitch. This makes a rounded root thread rather than flat root, though a flat crest.
When we grind a tool by hand and put the calculated flat on it, that is also a compromise to true UN standards of having a rounded root but is more widely accepted than Sharp V or the .002" radius.