I agree. 1018 hrs is terrible to thread. But there are a few things to try.
You state that you turn a section to .500 dia.
I assume you meant to say that you turned a section to .375 for a length of
..500. If so, try going a little smaller. The book says you can go to a
minimum of .3691. Unless this is a very important part, I would go to about
..365 dia.. This will give you a flat on top of your thread which should
help with the burr. Also use a small triangular file to just kiss the burr.
With the lathe running, hold the file so that it is about 45 degrees to one
side of the thread and let it ride down the thread. Then hold it on the
other side and let it ride to the left again. Do this several times. Then,
make one more pass with the threading tool set at the final dimension that
you used before you used the file. This should clean up any burr you
created with the file.
You did not mention cutting oil. I like the old fashion sulfur oil. Good
luck

"Greg O" wrote in message
...

"Rob McDonald" wrote in message
...
I hope somebody has the patience to read through this :-) I am trying to
include all the details because I don't know what I am doing wrong.


I recently tried to cut a 3/8-40 thread on a piece of 1018 HRS. First
pass was smooth. With later passes the surface seemed to get rough,



1018 HRS, that is your problem!
Greg