Enter the "higbee" thread. Old timers used this for lathe or die-cut
threads. Begin threading with a chamfer. When done, use a small file,
filing parallel to the line of the thread (perpendicular to the bolt end)
and cut the sharp end of the thread away for 1/3 to 1/2 revolution. (This
may be more properly termed "relieving") Do this in a tapering fashion,
with the cut ending in full thread at the terminal point. Threads prepared
this way are easier to start in a hole without crossthreading. This is the
same theory that is used to "relieve" the threads of taps near the end - or
cause them to be pointed. Relieved threads are not so likely to break down
in tapping and are much easier to start.

Bob Swinney


"Richard J Kinch" wrote in message
. ..
How do you get a clean start to outside threads cut on a lathe? For
example, if you threaded the outside diameter of a rod, where the end of
the rod had been perpendicularly faced, a geometrically perfect thread
would end in a knife edge. Simply chamfering the corner doesn't really
get
rid of it all. Ideally you would want the thread that just suddenly ramps
up out of the minor diameter, like is formed on the end of a common
commercial bolt.